Butyrate prodrugs derived from lactic acid

TECHNICAL FIELD OF THE INVENTION

This invention relates to the use of butyrate prodrugs derived from lactic acid for treating inflammatory bowel disease. The invention also relates to the use of those prodrugs for the treatment of a chemotherapy-induced mucocutaneous side effect in a patient. The invention further relates to the use of butyrate prodrugs for treating lung, colo-rectal or prostate cancer. And the invention also relates to the use of butyrate prodrugs to treat cystic fibrosis and to enhance the efficiency of gene therapy.

BACKGROUND OF THE INVENTION

Following the observation that butyric acid induces cell differentiation in vitro [A. Leder and P. Leder, "Butyric Acid, a Potent Inducer of Erythroid Differentiation in Cultured Erythroleukemic Cells", Cell, 5, pp. 319-22 (1975)], that compound was found to demonstrate promising effects in leukemia patients, by inducing cell differentiation [A. Novogrodsky et al., "Effect of Polar Organic Compounds on Leukemic Cells", Cancer, 51, pp. 9-14 (1983)]. Aside from their use in treating .beta.-hemoglobinopathies, butyrate derivatives such as arginine butyrate, an arginine salt of butyric acid, have been shown to exert anti-tumor and anti-leukemia effects in mice [C. Chany and I. Cerutti, "Antitumor Effect Of Arginine Butyrate in Conjunction with Corynebacterium parvum and Interferon", Int. J. Cancer, 30, pp. 489-93 (1982); M. Otaka et al., "Antibody-Mediated Targeting of Differentiation Inducers To Tumor Cells: Inhibition of Colonic Cancer Cell Growth in vitro and in vivo", Biochem. Biophys. Res. Commun., 158, pp. 202-08 (1989); O. Vincent-Fiquet, J. C. Rogez, F. Boitte, M. Brazier and G. Desmet, "Effects of Arginine Butyrate and Tributyrylxylitol on Cultured Human Sarcoma Cells", Anticancer Research, 14, pp. 1823-28 (1994)].

Sodium butyrate has been found to induce apoptosis in retinoblastoma cell lines [Robert M. Conway, Michele C. Madigan, Philip L. Penfold and Francis A. Billson, "Induction of Apoptosis by Sodium Butyrate in the Human Y-79 Retinoblastoma Cell Line", Oncology Research, Vol. 7, No. 6, pp. 289-97 (1995)] and modify antigen expression in pancreatic cancer cells [Stefano Corra, Katherine Kazakoff, Masatoshi Mogaki, Martin Cano, and Parviz M. Pour, "Modification of Antigen Expression in Human and Hamster Pancreatic Cancer Cell Lines Induced by Sodium Butyrate", Teratogenesis, Carcinogenesis, and Mutagenesis, 13, pp. 199-215 (1993)].

The differentiating ability of butyrates is enhanced when administered in conjunction with other active agents. The combination of butyrates with the active metabolite of vitamin D shows enhanced differentiation of human colonic carcinoma cells in vitro [Y. Tanaka, K. K. Bush, T. M. Klauck, P. Higgins, "Enhancement of Butyrate Induced Differentiation of HT-29 Human Colon Carcinoma Cells by 1,25-Dihydroxyvitamin D.sub.3 ", Biochem. Pharmacol. 38, pp. 3859 (1989)]. Other agents known to exhibit this synergism with butyrates include all trans-retinoic acid [Z. Chen and T. Breitman, "Tributyrin: A Prodrug of Butyric Acid for Potential Clinical Application in Differentiation Therapy", Cancer Res., 54, pp. 3494-99 (1994)], TNF-.alpha. (Tumor Necrosis Factor) [Yifan Zhai et al, Development and Characterization of Recombinant Adenoviruses Encoding MART1 or gp100 for Cancer Therapy, The Journal of Immunolgy, pp. 700-710 (1996)] and dibutyryl adenosine-3',5'-cyclic monophosphate [Paul S. Ebert and Michael Salcman, "Differentiation Therapy Is Potentiated by Chemotherapy and Hyperthermia in Human and Canine Brain Tumor Cells In Vitro", Neurosurgery, Vol. 34, No. 4, pp. 657-663 (1994)].

Butyrates have also been tested for use in combination therapy in conjunction with a known therapeutic agent. A combination of Inteleukin 2 and sodium butyrate has been investigated for treatment of colo-rectal cancer [Pacale Perrin et al, An Interleukin 2/Sodium Butyrate Combination as Immunotherapy for Rat Colon Cancer Peritoneal Carcinomatosis, Gastroenterology, 107, pp. 1697-1708 (1994)].

Butyrate salts induce differentiation of colon cancer cell lines and arrest the growth of neoplastic colonocytes [O. C. Velazquez, H. M. Lederer, and J. L. Rombeau, "Butyrate and the Colonocyte. Implications for Neoplasia", Dig. Dis. Sci., 41, pp. 727-39 (1996)]. Sodium butyrate has been shown to induce apoptosis in colorectal carcinoma cell lines and to inhibit urokinase plasminogen activator and its receptor mRNA expression in colon cancer cell lines [A. Hague, D. J. Elder, D. J. Hicks, and C. Paraskeva, "Apoptosis in Colorectal Tumour Cells: Induction by the Short Chain Fatty Acids Butyrate, Propionate And Acetate and by the Bile Salt Deoxycholate", Int. J. Cancer, 60, pp. 400-6 (1995); Jinjin Dang, Yao Wang and William F. Doe, "Sodium Butyrate Inhibits Expression Of Urokinase And Its Receptor mRNAs At Both Transcription And Post-transcription Levels In Colon Cancer Cells", FEBS Letts., 359, pp. 147-50 (1995)]. Butyrates, in conjunction with a known therapeutic agent, are known to be effective in the apoptosis of colon cancer cells [John A. McBain et al, "Phorbol Ester Augments Butyrate-Induced Apoptosis Of Colon Cancer Cells", Int. J. Cancer, 67, pp. 715-723 (1996)].

In addition to colon cancer, butyrates have been investigated for the treatment of inflammatory bowel diseases, such as colitis and Crohn's disease. Butyrates enhance the synthesis of colonic mucin, a glycoprotein present in the colonic mucus. The mucus adheres to the colonic epithelium, thereby preventing invasion by colonic bacteria and protecting against damage by bacterial toxins and enzymes. Butyrate enemas are used in the treatment of diversion colitis and ulcerative colitis [W. Frankel et al, "Butyrate Increases Colonocyte Protein Synthesis In Ulcerative Colitis", Journal of Surgical Research, 57, pp. 210-214 (1994); A. Finnie et al, "Colonic Mucin Synthesis is Increased by Sodium Butyrate", Gut, 36, pp. 93-99 (1995)].

More recently, it has been suggested that butyrate may be beneficial in the treatment of cystic fibrosis (CF) by properly directing the mutant, but functional gene product of the CFTR gene to the plasma membrane [S. H. Cheng et al., Am. J. Physiol., 268, pp. L615-L624 (1995)]. Most forms of CF are linked to a mutation in the CFTR gene which causes the expressed protein to be mislocalized to the endoplasmic reticulum, rather than the plasma membrane. The CFTR gene product is a chloride ion channel. The mutant gene product retains partial ability to function as a chloride channel, but its mislocalization renders that function useless [C. Li et al., Nat. Genet., 3, pp. 311-316 (1993); G. M. Denning et al., Nature, 358, pp. 761-764 (1992)].

In connection with gene therapy, it has been shown that retroviral expression of the wild-type CFTR gene is enhanced in the presence of butyrate [J. C. Olsen et al., Hum. Gene Ther., 6, pp. 1195-1202 (1995)].

The drawbacks of all of these methods is that the forms of butyrate utilized are characterized by poor pharmacokinetics. For example, butyrate salts have the advantage of low toxicity as compared with conventional chemotherapeutic agents, but their short half-lives in vivo have been viewed as a potential obstacle in clinical settings [A. Miller et al., "Clinical Pharmacology of Sodium Butyrate in Patients with Acute Leukemia", Eur. J. Clin. Oncol., 23, pp. 1283-87 (1987); Novogrodsky et al., supra]. The rapid clearance of these agents results in an inability to deliver and maintain high plasma levels of butyrate which necessitates administration by intravenous infusion. Another potential obstacle to the use of butyrate salts is salt overload and its physiological sequelae.

In view of these observations, various prodrugs of butyric acid have been proposed for use in .beta.-hemoglobinopathy and leukemia differentiation therapies. Such prodrugs include tributyrin and n-butyric acid mono- and polyesters derived from monosaccharides [Z. Chen and T. Breitman, "Tributyrin: A Prodrug of Butyric Acid for Potential Clinical Application in Differentiation Therapy", Cancer Res., 54, pp. 3494-99 (1994); H. Newmark et al., "Butyrate as a Differentiating Agent: Pharmacokinetics, Analogues and Current Status", Cancer Letts., 78, pp. 1-5 (1994); P. Pouillart et al., "Pharmacokinetic Studies of N-Butyric Acid Mono- and Polyesters Derived From Monosaccharides", J. Pharm. Sci., 81, pp. 241-44 (1992); C. Calabresse et al, "Selective Induction Of Apoptosis In Myeloid Leukemic Cell Lines By Monoacetone Glucose-3 Butyrate", Biochem. Biophys. Res. Comm., Vol. 201, No. 1, pp. 266-82 (1994)].

Such butyrate prodrugs have not proved useful as therapeutics, however, due to factors such as short half-life, low bioavailability, low C.sub.max, or lack of effective oral deliverability. Other prodrugs, such as AN-9 and AN-10 [A. Nudelman et al., "Novel Anticancer Prodrug of Butyric Acid", J. Med. Chem., 35, pp. 687-94 (1992)], elicit metabolites that may produce formaldehyde in vivo, leading to toxic effects in patients.

Accordingly, the need exists for forms of butyrate having desirable pharmacokinetic properties for use in providing effective therapy for the target diseases discussed above.

DISCLOSURE OF THE INVENTION

The present invention solves these problems by providing butyrate prodrugs of lactic acid and pharmaceutical compositions comprising them. These butyrate prodrugs demonstrate good bioavailability, effective oral deliverability, good half-life and surprisingly high C.sub.max.

When administered to a patient, the butyrate prodrugs in these compositions release butyrate more efficiently than prior art butyrate prodrugs. This produces a higher plasma level of butyrate relative to the amount of prodrug administered as compared to the prior art butyrate prodrugs.

Butyrate released from these prodrugs can stimulate cell differentiation and thus has an anti-proliferative effect on malignant cells, particularly malignant hemopoietic cells. Thus, the compounds and pharmaceutical compositions of this invention may be employed in methods for treating cancer, particularly malignant hematological and colo-rectal disorders.

These prodrugs and compositions comprising them can also be employed in the treatment of inflammatory bowel disorders, cystic fibrosis and in enhancing the efficacy of gene therapy.

Because a patient can be treated with lower doses of the present prodrugs in order to achieve a desired serum butyrate concentration, toxicity associated with the non-butyrate portion of the prodrug is less of a concern.

All of these features facilitate the chronic therapy regimens often prescribed for patients suffering from cancer, inflammatory bowel disorders, cystic fibrosis, as well as patients undergoing gene therapy. At the same time, they also facilitate convenient dosing schemes for and patient compliance with such therapy regimens. Furthermore, the methods and compositions of this invention are not beset by the variety of side effects which typically characterize conventional therapy regimens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the time course of plasma butyric acid concentration following administration of the various doses of compound IIIc in individual monkeys.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

The following definitions are used throughout the application.

A used herein, the term "alkyl", alone or in combination with any other term, refers to a straight-chain or branched-chain aliphatic hydrocarbon radical containing the specified number of carbon atoms, or where no number is specified, preferably from 1 to 10 carbon atoms, which may contain one or more unsaturated bonds. Examples of alkyl radicals include, but are not limited to, methyl, ethyl, isopropyl, butyl, pentyl and the like. The term "alkyl", as used herein also includes the terms "alkenyl" and "alkynyl", which are defined below.

The term "alkenyl", alone or in combination, refers to a straight-chain or branched-chain alkenyl radical containing 2 to 10 and more preferably from 2 to 6 carbon atoms. Examples of alkenyl radicals include, but are not limited to, vinyl, allyl, E-propenyl, Z-propenyl, E,E-hexadienyl, E,Z-hexadienyl, Z,Z-hexadienyl and the like.

The term "alkynyl", alone or in combination, refers to a straight-chain or branched chain alkynyl radical containing from 2 to 10 and more preferably from 2 to 6 carbon atoms. Examples of such radicals include, but are not limited to, ethynyl (acetylenyl), propynyl, propargyl, butynyl, 1,4-hexydiynyl, decynyl and the like. "Alkynyl", as used herein, also refers to radicals containing both carbon-carbon double bonds and carbon-carbon triple bonds, such as Z-pent-2-en-4ynyl.

The term "carbocyclyl", alone or in combination with any other term, refers to a carbocyclic radical, which may be saturated, partially unsaturated or aromatic, containing the specified number of carbon atoms, preferably from 3 to 14 carbon atoms and more preferably from 5 to 10 carbon atoms. The term "carbocyclic" as defined include radicals of "cycloalkyls", "cycloalkenyls" and carbocyclic "aryls". Carbocyclyl also refers to radicals containing several carbocyclic rings, which are fused or spiro-fused, comprising from 4 to 14 carbon atoms.

The term "cycloalkyl", alone or in combination, refers to a cyclic alkyl radical containing from 3 to 8, preferably from 3 to 6, carbon atoms. Examples of such cycloalkyl radicals include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and the like.

The term "cycloalkenyl", alone or in combination, refers to a cyclic alkyl radical containing from 4 to 8, preferably from 5 to 6, carbon atoms and one or more double bonds. Examples of such cycloalkenyl radicals include, but are not limited to, cyclopentenyl, cyclohexenyl, cyclopentadienyl and the like.

The term "heterocyclyl" refers to a carbocyclyl, preferably of 5 to 7 atoms, containing from 1-4 heteroatoms independently selected from oxygen, nitrogen and sulfur in place of an equal number of carbon atoms. That term also refers to substituted or unsubstituted, 8-11 membered bicyclic ring systems, which may be aromatic or non-aromatic containing in either or both rings from 1-4 heteroatoms independently selected from oxygen, nitrogen and sulfur and wherein the terms nitrogen and sulfur may include any oxidized form of nitrogen and sulfur and the quarternized form of any basic nitrogen. A heterocyclyl group may be connected to a structure through any atom of the group which results in a stable chemical bond.

Examples of non-aromatic heterocyclic radicals include, but are not limited to, 2-pyrrolinyl, 3-pyrrolinyl, 1,3-dioxolyl, 2H-pyranyl, 4H-pyranyl, piperidyl, 1,3-dioxanyl, 1,4-dioxanyl, morpholinyl, 1,4-dithianyl, thiomorpholinyl, thiomorpholinyl sulfone, tetrahydrofuryl, piperazinyl and quinuclidinyl.

Examples of aromatic heterocyclic radicals include, but are not limited to, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, pyrrolyl, oxazolyl, thiazolyl, imidazolyl, pyrazolyl, 2-pyrazolinyl, pyrazolidinyl, isoxazolyl, isothiazolyl, 1,2,3-oxadiazolyl, 1,2,3-triazolyl, 1,3,4-thiadiazolyl, pyridazinyl, pyrimidinyl, pyrazinyl, 1,3,5-triazinyl, 1,3,5-trithianyl, indolizinyl, indolyl, isoindolyl, 3H-indolyl, indolinyl, benzo[b]furanyl, benzo[b]thiophenyl, 1H-indazolyl, benzimidazolyl, benzthiazolyl, purinyl, 4H-quinolizinyl, quinolinyl, isoquinolinyl, cinnolinyl, phthalazinyl, quinazolinyl, quinoxalinyl, 1,8-naphthyridinyl, pteridinyl, carbazolyl, acridinyl, phenazinyl, phenothiazinyl, phenoxazinyl and the like.

The term "aryl" refers to an aromatic carbocyclic group, preferably of 6 atoms, or an 8-14 membered aromatic polycyclic aromatic ring system;

Examples of "aryl" groups, include, but are not limited to, phenyl, 1-naphthyl, 2-naphthyl, indenyl, azulenyl, fluorenyl and anthracenyl.

When substituted, each "carbocyclyl" and "heterocyclyl" may independently contain one to three substituents that are independently selected from hydroxy; halogen; C(1-6)-straight or branched alkyl, alkylamino or alkoxy; C(2-6)-straight or branched alkenyl, alkenylamino, alkynylamino, alkynyl, alkenoxy or alkynoxy; nitro, NH.sub.2 ; thiol; alkylthio; carbocyclyl; carbocyclylalkyl; carbocyclylalkenyl; carbocyclylalkynyl; heterocyclyl; heterocyclylalkyl; heterocyclylalkenyl; heterocyclylalkynyl; methylenedioxy; carboxamido; alkylcarbonylamino; carbocyclylcarbonylamino; heterocyclylcarbonylamino; carbocyclylalkylcarbonylamino; heterocyclylalkylcarbonylamino; sulfonamido; alkylsulfonamido; alkenylsulfonamido; alkynylsulfonamido; and arylsulfonamido. The substituents listed above may be attached to either a ring carbon atom or a ring heteroatom.

The term "alkoxy" refers to an O-C(1-6)-straight or branched alkyl radical. Examples of alkoxy radicals include, but are not limited to, methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, isobutoxy, sec-butoxy and tert-butoxy.

The term "alkenoxy" refers to an O-C(2-6)-straight or branched alkenyl radical. Examples of alkenoxy radicals include, but are not limited to, allyloxy, E and Z-3-methyl-2-propenoxy.

The term "alkynoxy" refers to an O-C(2-6)-straight or branched alkynyl radical. Examples of alkenoxy radicals include, but are not limited to, propargyloxy and 2-butynyloxy.

The term "alkylamino" refers to a C(1-6)-straight or branched alkyl-NH radical or a C(1-6)-straight or branched alkyl-N-C(1-6)-straight or branched alkyl radical where the alkyl radicals may be the same or different. Examples of suitable alkylamino radicals include, but are not limited to, methylamino, ethyl amino, propylamino, isopropyl amino, t-butyl amino, N,N-diethylamino and N,N-methylethylamino.

The term "alkenylamino" refers to a C(2-6)-straight or branched alkenyl-NH radical, a C(2-6)-straight or branched alkenyl-N-C(1-6)-straight or branched alkyl radical, or a C(2-6)-straight or branched alkenyl-N-C(2-6)-straight or branched alkenyl radical where the alkenyl radicals may be the same or different. An example of a suitable alkenyl amino radical is, but is not limited to, allylamino. Alkenylamino also refers to methyl allylamino, di-2-propenylamino and tert-butyl-3,5-hexadienylamino.

The term "alkynylamino" refers to a C(3-6)-straight or branched alkynyl-NH radical, a C(3-6)-straight or branched alkynyl-NH-C(1-6)straight or branched alkyl radical, a C(3-6)-straight or branched alkynyl-NH-C(2-6)straight or branched alkenyl radical, or a C(3-6)-straight or branched alkynyl-N-C(3-6)-straight or branched alkynyl radical where the alkynyl radicals may be the same or different. An example of a suitable alkynyl amino radical is, but is not limited to, propargylamino and the like.

The term "amido" refers to a --C(O)NH.sub.2 radical.

The term "alkylamido" refers to a --C(O)NH-C(1-6)-straight or branched chain alkyl radical or a --C(O)N-[C(1-6)].sub.2 -straight or branched chain alkyl radical, wherein the two C(1-6)-straight or branched alkyl chains may be the same or different.

The term "alkylsulfonamido" refers to a C(1-6) straight or branched chain alkyl-S(O).sub.2 NH-- radical. An example of alkylsulfonamido is ethanesulfonamido.

In order that the invention herein described may be more fully understood, the following detailed description is set forth.

The compounds of this invention are butyrate prodrugs derived from lactic acid, which are represented by the Formula I: ##STR1##

wherein A and D are independently selected from the group consisting of hydrogen, alkoxyalkyl, carbocyclylalkoxyalkyl, C(1-4)-straight or branched alkyl, or C(2-4)-straight or branched alkenyl or alkynyl, any of which may be independently substituted with hydroxy, alkoxy, carboxyalkyl, alkylamido, arylamido, heterocyclylamido, aralkylamido, heterocyclylalkylamido, alkoxycarbonylamino, alkenoxycarbonylamino, carbocyclyloxycarbonylamino, heterocyclyloxycarbonylamino, carbocyclylalkoxycarbonyl-amino, heterocyclylalkoxycarbonylamino, alkoxyalkoxycarbonylamino, amino, amido, carboxyl, thiol, thioalkyl, thiophenyl, aryl and heterocyclyl; provided that A and D are not simultaneously hydrogen;

R is O, NH, NC(1-5)-straight or branched alkyl or NC(2-5)-straight or branched alkenyl; any of which is optionally substituted with a carbocyclyl or heterocyclyl moiety;

Z is hydrogen, C(1-4)-straight or branched alkyl, C(2-4)-straight or branched alkenyl or alkynyl, carbocyclyl, or heterocyclyl; any of which is optionally substituted with 1 or 2 groups independently chosen from C(1-3)-alkyl, C(2-3)-alkenyl or alkynyl, alkoxy, alkenoxy, alkynoxy, amido, thioalkyl, carbocyclyl or heterocyclyl; and

each stereogenic carbon may be in the R or S configuration;

provided that said compound is not ##STR2##

According to a preferred embodiment, D is methyl and A is hydrogen in the compound of Formula I, yielding a compound of Formula II: ##STR3##

Preferably, in formula II, R is O, NH, NC(1-3)-alkyl, NC(2-4)-straight or branched alkenyl or N-benzyl; and Z is C(1-4)-straight or branched alkyl optionally substituted with a 5 to 10-membered carbocyclyl or heterocyclyl. Most preferably, R is O, Z is an unsubstituted C(1-4)-straight or branched alkyl, and the stereochemistry at the methyl-bearing carbon is S.

According to another preferred embodiment, R is oxygen in Formula I, producing a compound of formula III: ##STR4##

Preferably, in Formula III, A and D are independently selected from hydrogen, methyl, ethyl or allyl; provided that A and D are not both hydrogen; and Z is C(1-3)-alkyl optionally substituted with a C(5-10)-carbocyclyl or -heterocyclyl.

More preferably, in Formula III, D is hydrogen or methyl, A is unsubstituted C(1-3)-alkyl and Z is unsubstituted C(1-3)-alkyl.

The more preferred pharmaceutical compositions of this invention comprise a compound selected from: ##STR5##

The most preferred prodrug is that depicted as compound IIIc.

The prodrugs of Formula I contain one or more asymmetric carbon atoms and thus occur as racemates and racemic mixtures, single enantiomers, diastereomeric mixtures and individual diastereomers. All such isomeric forms of these compounds, as well as mixtures thereof, are included in the pharmaceutical compositions of the present invention.

This invention also encompasses prodrugs of Formula I that are quarternized at any of the basic nitrogen-containing groups. The basic nitrogen can be quarternized with any agents known to those of skill in the art including, for example, lower alkyl halides, such as methyl, ethyl, propyl and butyl chloride, bromides and iodides; dialkyl sulfates, including dimethyl, diethyl, dibutyl and diamyl sulfates; long chain halides, such as decyl, lauryl, myristyl and stearyl chlorides, bromides and iodides; and aralkyl halides, including benzyl and phenethyl bromides. Water or oil-soluble or dispersible products may be obtained by such quarternization.

Prodrugs are hydrolyzed in vivo to release the active ingredient. In the case of the present invention, the disclosed prodrugs release butyric acid. Without being bound by theory, we believe that a threshold concentration of butyric acid in the plasma is required to be maintained for a period of at least several hours during the day over a number of days to induce production of gamma globin chain synthesis and fetal hemoglobin formation, or to induce differentiation in malignant cells, leading to an anticancer effect.

The compounds that characterize the compositions of this invention are metabolized in the body in such a way as to produce a high maximal concentration (C.sub.max) of butyric acid following oral administration. These compounds are also characterized by a sufficiently long half-life (t.sub.1/2) that ensures good exposure of the patient to butyric acid. Due to the surprising and unexpectedly high C.sub.max, less of these prodrugs need to administered to produce effective plasma concentration of butyric acid than conventional agents. This, in turn, results in lower potential for toxicity due to the carrier portion of the prodrug, as well as easier administration.

The butyrate prodrugs of this invention may be synthesized by standard organic routes. Many .alpha.-hydroxy acids, .alpha.-hydroxy esters and .alpha.-hydroxy amides are commercially available (e.g., Aldrich Catalog Handbook of Fine Chemicals, 1994-1995). In the case of .alpha.-hydroxy esters or .alpha.-hydroxy amides, derivatization of the hydroxy group may be carried out using an activated form of butyric acid, such as an acid chloride; symmetrical acid anhydride; mixed carbonic, phosphonic, or sulfonic acid anhydrides; and activated esters such as phenyl, 4-nitrophenyl, pentafluorophenyl, hydroxybenzotriazolyl or N-hydroxysuccinimidyl.

Preferably the derivatization is carried out using a base such triethylamine, diisopropylethylamine, 1,8-diazabicyclo[54.0] undec-7-ene, pyridine or tetramethylguanidine; or aqueous buffers or bases such as sodium carbonate or sodium hydrogen carbonate (see, e.g. E. Haslam, "Recent Development in Methods for the Esterification and Protection of the Carboxyl Group", Tetrahedron, 36, pp. 2409-2433 (1980). Dehydrating agents, such as 1,3-dicyclohexylcarbodiimide or 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride may also be employed. The inclusion of a hyperacylation catalyst, such as 4-dimethylaminopyridine, may improve the efficiency of the reaction (A. Hassner et al., "Direct Room Temperature Esterification of Carboxylic Acids", Tetrahedron Lett., 46, pp. 4475-4478 (1978)). Additional methods are well known in the art and may be readily substituted for those listed above.

If .alpha.-hydroxy acids are used, derivatization of the carboxylic acid group may be carried out by first converting the hydroxy group to a butyryl group. This is followed by esterification or amidification of the carboxylic acid, or alternatively by performing a sequence comprising the steps of:

1) transiently blocking the hydroxyl with a removable protecting group;

2) derivatizing the carboxylic acid as an ester or amide;

3) removing the hydroxyl protecting group; and

4) converting the hydroxy group to a butyryl group as above.

The butyrated or hydroxyl-protected .alpha.-hydroxy acids may then be converted to their corresponding esters of Formula I (wherein R=O) by carboxyl activation, similar to that described above for butyric acid, followed by reaction with an alcohol in the presence of a suitable base. Reaction of the activated butyrated or hydroxyl-protected .alpha.-hydroxy acids with primary or secondary amines yields amines of Formula I (wherein R=NH, N-C(1-5)-straight or branched chain alkyl, or N-C(2-5)-straight or branched chain alkenyl which may be substituted with a carbocyclyl or heterocyclyl moiety). A wide variety of primary, secondary and tertiary alcohols and primary and secondary amines are commercially available or readily produced by methods known in the art. Therefore, this process provides access to compounds of Formula I where R-Z may vary greatly.

Some particularly useful methods for synthesizing compounds of Formula I are shown in Scheme I, below. ##STR6##

In these methods, the .alpha.-hydroxy acid of choice is simultaneously reacted at the hydroxyl and carboxylate groups. Reaction with a suitable silylating reagent, for instance t-butyl-dimethylsilyl chloride in the presence of imidazole in dimethyl formamide, yields a bis-silylated compound of Formula XIa or similar silyl derivative. This compound can be converted to a carboxyl-activated derivative by a sequence comprising:

1) partial hydrolysis of carboxyl silyl group, for instance by hydrolysis using about 1 molar equivalent of lithium hydroxide at about -20.degree. C. to about ambient temperature in aqueous dioxane;

2) concentration in vacuo;

3) careful acidification using for instance citric acid;

4) extraction into a suitable organic solvent such as methylene chloride; and

5) carboxyl activation as described above.

Removal of the hydroxyl-protecting silyl group using, for instance, tetrabutylammonium fluoride in tetrahydrofuran at about 0.degree. C. to ambient temperature, or HF-pyridine complex in acetonitrile, yields the hydroxy derivative XIV. Conversion to compounds of Formula I may then be effectuated as described above.

Alternatively, the .alpha.-hydroxy acid of Formula X is simultaneously reacted at the hydroxyl and carboxylate groups with an alkyl substituent such as a benzyl derivative as shown in scheme I. Other alkyl derivatives such as allyl, 4-methyloxybenzyl, 2,2,2-trichloroethyl or 2-trimethylsilylethyl may also be used in this step.

The derivatization step may be accomplished by reaction of the compound of Formula X with excess benzyl bromide in the presence of about 2.2-3 equivalents of a strong base, such as sodium hydride, potassium hydride, or potassium t-butoxide, in a suitable inert solvent, such as THF or dimethylformamide, at about -30.degree. C. to about 100.degree. C. depending on the particular .alpha.-hydroxy acid and electrophile. Optionally, a phase-transfer catalytic method using a base such as K.sub.2 CO.sub.3 or NaOH in an inert solvent, such as toluene or acetonitrile, may be used for this alkylation. Suitable catalysts include quartenary ammonium salts, such as .sup.n Bu.sub.4 N.sup.+ Br.sup.-, and crown ethers, such as dibenzo-18-crown-6.

Conversion of suitably bis-alkylated compounds of Formula XIb to those of Formula XIIb may be accomplished by saponification, for instance in aqueous methanol or diaoxane, using an equimolar or greater amount of alkali metal base, such as hydroxides of sodium, lithium or potassium, at temperature ranging from about -40.degree. C. to about 80.degree. C. Alternatively, reaction with a thiolate anion, such as sodium ethyl thiolate, idotrimethylsilane or with other ester-deprotecting reagents, will yield the protected carboxylic acid of Formula XIIb (see. e.g., R. C. Larock, "Comprehensive Organic Transformations", pp. 981-985, 1989 VCH Publishers, Inc., New York, N.Y.).

Activation and derivatization similar to that described for compounds of Formula XIIa yield compounds of Formula XIIIb. The benzyl group may be then conveniently removed, e.g., by catalytic hydrogenation using for instance palladium or rhodium metal dispersed on carbon, using a hydrogen source such as hydrogen gas or ammonium formate, or catalytic transfer hydrogenation using cyclohexadiene or the like. Such methods are well known in the art of organic chemistry (see, e.g., P. N. Rylander, "Catalytic Hydrogenation in Organic Synthesis", .COPYRGT.1979 Academic Press, Inc., Orlando, Fla.). Reducing metal methods, involving dissolving the substrate in liquid ammonia and adding an alkali metal, such as metallic sodium, are also known in the art.

If an allyl group is used in place of a benzyl group, its removal may be effectuated by palladium transfer reactions using e.g. tetrakis(triphenylphosphine)Pd.sup.0 and an allyl acceptor, such as morpholine or Pd.sup.II acetate and Bu.sub.3 SnH. Methods for employing these and other alcohol protecting groups are described in the art (see. e.g., T. W. Greene and P. G. M. Wuts "Protective Groups in Organic Synthesis", Second Edition .COPYRGT.1991 Academic Press, Inc., Orlando, Fla., pp. 14-120). The resulting compound of Formula XII may then be reacted as described above to produce compounds of Formula I.

.alpha.-Hydroxy acids, .alpha.-hydroxy esters and .alpha.-hydroxy amides, when not commercially available, may conveniently be synthesized by a variety of methods which will be readily apparent to those of skill in the art. For instance, reaction of a glyoxylic acid ester or amide with a suitable carbon-based nucleophile, such as a Grignard reagent, organocuprate or an organolithium reagent, in a suitable inert solvent, such as diethyl ether or tetrahydrofuran, at about -80.degree. C. to about 0.degree. C., will yield a .alpha.-hydroxy ester or amid of Formula XIV where A is the nucleophile and D is hydrogen. Similar reactions, carried out on .alpha.-ketoesters or amides, yield .alpha.,.alpha.-disubstituted, .alpha.-hydroxyesters or amides (B. M. Trost and I. Fleming, "Comprehensive Organic Syntheses, Vol. I" pp. 49-282 .COPYRGT.1989, Pergamon Press, Oxford, England).

Many .alpha.-hydroxy acids may be produced conveniently by reacting the corresponding .alpha.-amino acids with a diazetizing agent in a poorly nucleophilic medium. For example, NaNO.sub.2 may be added to a solution of amino acid in aqueous sulfuric acid (R. V. Hoffman et al., "Preparation of (r)-2-Azido Esters from 2-((p-Nitrobenzene)sulfonyl)oxy Esters and Their Use as Protected Amino Acid Equivalents for the Synthesis of Di- and Tripeptides Containing D-Amino Acid Constituents", Tetrahedron Lett., 48, pp. 3007-3020 (1992)). Since numerous .alpha.-amino acids may be purchased and many others can be made by known synthetic routes, often in optically active forms, (H. K. Chenault et al., "Kinetic Resolution of Unnatural and Rarely occurring Amino Acids: Enantioselective Hydrolysis of N-Acyl Amino Acids Catalyzed by Acylase I", J. Am. Chem. Soc., 111, pp. 6354-6364 (1989)), this method provides a ready source of starting materials of Formula I.

Alkyl carboxylic acids and their ester and amide derivatives may be converted to .alpha.-hydroxy derivatives by formation of an anion at the carbon .alpha. to the carboxylate derivative, followed by reaction with an oxygenating agent, such as N-sulfonyl oxaziradines, yield the compound of Formula X or XIV (R. C. Larock, "Comprehensive Organic Transformations", p. 489, .COPYRGT.1989 VCH Publishers, Inc., New York, N.Y.).

Variations of the methods disclosed above and other synthetic approaches known in the literature of synthetic organic chemistry will be apparent to those or ordinary skill in the art. Alternate transient protection and deprotection of reactive groups and their further transformation to produce additional compounds of Formula I, will be readily apparent the skilled artisan.

According to one embodiment, the invention provides a method for treating a patient suffering from a disease characterized by neoplastic, tumorigenic or malignant cell growth by administering to said patient a pharmaceutical composition comprising a compound of this invention and a pharmaceutically acceptable carrier. The term "treatment", as used herein, includes prevention of progression of the disease or its recurrence. Such diseases include carcinomas, myelomas, melanomas, lymphomas and leukemias. Preferably, the method is used for treating lung cancer, colo-rectal cancer and prostate cancer.

Pharmaceutically acceptable salts of the compounds of Formula I (including the n-butyl ester specifically excluded from the compounds of this invention) may also be employed in any of the above-described compositions. Such salts may be derived from pharmaceutically acceptable inorganic and organic acids and bases.

Examples of suitable acids include hydrochloric, hydrobromic, sulfuric, nitric, perchloric, fumaric, maleic, phosphoric, glycollic, lactic, salicylic, succinic, toluene-p-sulfonic, tartaric, acetic, citric, methanesulfonic, ethanesulfonic, formic, benzoic, malonic, naphthalene-2-sulfonic and benzenesulfonic acids.

Salts derived from appropriate bases include alkali metal (e.g., sodium), alkaline earth metal (e.g., magnesium), ammonium and N-(C.sub.1-4 alkyl).sub.4.sup.+ salts.

The carriers and adjuvants present in the compositions of this invention include, for example, ion exchangers, alumina, aluminum stearate, lecithin, serum proteins, such as human serum albumin, buffer substances, such as phosphates, glycine, sorbic acid, potassium sorbate, partial glyceride mixtures of saturated vegetable fatty acids, water, salts or electrolytes such as protamine sulfate, disodium hydrogen phosphate, sodium chloride, zinc salts, colloidal silica, magnesium, trisilicate, polyvinyl pyrrolidone, cellulose-based substances and polyethylene glycol. Adjuvants for topical or gel base forms may be selected from the group consisting of sodium carboyxmethylcellulose, polyacrylates, polyoxyethylene-polyoxypropylene-block polymers, polyethylene glycol and wood wax alcohols.

Generally, the pharmaceutical compositions utilized in the methods of this invention may be formulated and administered to the patient using methods and compositions similar to those employed for other pharmaceutically important agents. Any pharmaceutically acceptable dosage route, including, oral, topical, intranasal, or parenteral (including intravenous, intramuscular, subcutaneous, intracutaneous, periosteally, intra-articular, intrasynovial, intrathecal, intrasternal, intracranial or intralesional) may be used.

The pharmaceutical compositions utilized in the methods of this invention may be provided in a variety of conventional depot forms. These include, for example, solid, semi-solid and liquid dosage forms, such as tablets, pills, powders, liquid solutions, dilutions, suspensions, emulsions, liposomes, capsules, suppositories, injectable and infusible solutions. The preferred form depends upon the intended mode of administration and therapeutic application.

For example, oral administration of the pharmaceutical compositions of this invention may be by any orally acceptable dosage form including, but not limited to, capsules, tablets, and aqueous or non-aqueous suspensions, emulsions, oil dilutions and solutions. In the case of tablets for oral use, carriers which are commonly used include lactose and corn starch. Lubricating agents, such as magnesium stearate, are also typically added. For oral administration in a hard gelatin capsule form, useful diluents include lactose and dried corn starch. Soft gelatin capsules incorporating oils and/or polyethylene glycols excipients may also be used. Fluid unit dosage forms for oral administration include shakes, syrups and suspensions. When aqueous suspensions or emulsions are administered orally, the prodrug is combined with emulsifying and suspending agents. Flavoring, sweetening, or coloring agents may be added, if desired.

Preferably, the pharmaceutical compositions utilized in the methods of this invention are formulated for oral or rectal administration. Even more preferred are oral emulsions comprising between about 5 to 40% (w/w) of the prodrug of Formula I (including the n-butyl ester specifically excluded form the compounds of this invention) and an ionic or non-ionic surfactant with the resulting composition having an HLB value of between 0-40. Preferred surfactants include Tween-20, Tween-80, Spam-20, Spam-40 and poloxamers, such as S-108.

A preferred form of rectal administration uses a rectal suppository or enema using a suitable fluid dosage forms. An enema is a more preferred form of rectal administration.

Preferably, the methods of this invention utilize a pharmaceutical composition comprising an amount of the disclosed butyrate prodrug to provide a plasma butyric acid concentration of between about 0.03 mM and 3.0 mM within 8 hours of administration. More preferably, the prodrug of Formula I is utilized in an amount that produces a plasma butyric acid concentration of between about 0.1 mM and 1.0 mM within 6 hours of administration. Most preferably, the prodrug is utilized in an amount that produces a plasma butyric acid concentration of between about 0.1 mM and 1.0 mM within 2 hours of administration and the concentration remains within that range for at least 2 hours. These same amounts are also effective to treat the diseases discussed below and to enhance gene therapy.

Dosages of between about 25 mg prodrug/kg body weight and 3 g prodrug/kg body weight administered one or more times per day are capable of producing the desired plasma butyric acid concentration. Preferably, the patient will be administered the prodrug between 1 and 4 times per day.

Preferably, for the treatment of colo-rectal cancer or prostate cancer, a formulation suitable for oral or rectal administration is used.

According to another embodiment, the above-described method of treating cancers comprises the additional step of treating the patient with an active agent that enhances the differentiating ability of the prodrugs of the present invention. Preferably, that additional agent is one that is normally used to treat such malignancies. More preferably, that agent is hydroxyurea. That agent may be administered prior to, sequentially with, as a component of, or after treatment with the butyrate prodrug-containing composition.

The amount of conventional agent administered in these methods is preferably less than that normally required to treat such diseases in a monotherapy. The normal dosages of these conventional agents are well known in the art. Such agents include, erythropoietin, or cancer chemotherapeutic agents, such as hydroxyurea or 5-azacytidine or 3-thiacytidine. Hydroxyurea is a preferred conventional agent.

Combination therapies with conventional agents according to this invention (whether part of a single composition or administered separate from the prodrugs of this invention) may also exert an additive or synergistic effect, particularly when each component acts to treat or prevent the target disease via a different mechanism.

According to yet another embodiment, the invention provides a method for treating or preventing inflammatory bowel diseases. Such diseases include colitis, pouchitis and Crohn's disease. Preferably, this method provides the same serum butyric acid concentrations indicated above as being desirable for treating cancers. Preferably, the inflammatory bowel disease to be treated is colitis. More preferably, this method of treating colitis utilizes a formulation suitable for oral or rectal administration.

According to another embodiment, the present invention provides a method for treating chemotherapy-induced mucocutaneous side effects, such as alopecia. The amounts of butyrate prodrug of this invention utilized in this method are the same as those set forth above for use in the treatment of cancer and inflammatory bowel diseases.

According to another embodiment, the present invention provides a method for treating cystic fibrosis. In this method, the amount of the butyrate prodrug of this invention to be administered should be sufficient to at least partially restore plasma membrane chloride ion transport. This amount will be similar to the amounts utilized in the treatment of cancer, as set forth above.

Another embodiment of this invention provides a method of enhancing the efficiency of gene therapy. As discussed above, it has been previously shown that butyrate enhances the production of retroviral vectors expressing CFTR cDNA in a gene therapy model. In particular, it appears that butyrate allows active gene expression to continue for longer periods of time. This provides a solution to one of the problems associated with gene therapy--short-lived, transient expression of the recombinant gene of interest. The demonstrated ability of butyrate to enhance gene expression and to increase viral vector-encoded protein production, combined with the desirable pharmacokinetic properties of the butyrate prodrugs of this invention make these prodrugs an optimal choice for increasing the efficiency of gene therapy.

For use in enhancing the efficiency of gene therapy, the butyrate prodrugs of this invention may be formulated to be administered as a separate pharmaceutical composition, either simultaneously with or within 5 hours of the administration of the retroviral vector. Following initial administration, the butyrate prodrug will then be administered at a maintenance dose of between 10% and 90% of the doses used in the initial treatment. Preferably, the butyrate prodrug in the maintenance phase will be administered by constant infusion. The amount of the butyrate prodrug initially utilized in such methods will be the same as that utilized in cancer treatment.

According to a preferred embodiment, the gene therapy whose efficiency is to be enhanced is one in which the CFTR gene is contained in the retroviral vector.

In order that the invention described herein may be more fully understood, the following examples are set forth. It should be understood that these examples are set forth for illustrative purposes only and are not to be construed as limiting this invention in any manner.

EXAMPLE 1

Synthesis of Compound IIIa and IIIb

We synthesized compound IIIa as follows. We combined 6.25 ml of methyl (S)-lactate with 13.75 ml of Et.sub.3 N and then added that mixture to 50 ml of methylene chloride. We cooled this mixture to 0.degree. C. in an ice bath and then slowly added 8.2 ml of butyryl chloride. This mixture was stirred overnight and then filtered through a Buchner filter. The precipitate cake was then washed with ether and the wash was combined with the filtrate. The organic layer from the filtrate was isolated, washed twice with water, once with brine and then dried over anhydrous MgSO.sub.4. The crude yield was 12.48 g.

The material was then dissolved in 90% hexane/ethyl acetate and chromatographed on an MPLC column. Fractions containing the desired product were pooled and dried yielding 9.46 g of pure product. NMR analysis confirmed that the pure product was compound IIIa.

Compound IIIb was synthesized and purified in an identical manner, substituting methyl (R)-lactate for methyl (S)-lactate.

EXAMPLE 2

Synthesis of Compound IIIc

We synthesized compound IIIc by combining 7.4 ml of ethyl (S)-lactate with 13.75 ml of Et.sub.3 N and then added that mixture to 50 ml of methylene chloride. We cooled this mixture to 0.degree. C. in an ice bath and the slowly added 8.2 ml of butyryl chloride. This mixture was stirred overnight. TLC analysis of the mixture indicated incomplete reaction. We therefore added an additional 0.25 mole (2.5 ml) of butyryl chloride and allowed the reaction to continue with stirring for 24 hours.

The mixture was then filtered through a Buchner filter. The precipitate cake was then washed with ether and the was combined with the filtrate. The organic layer from the filtrate was isolated, washed twice with water, once with brine and then dried over anhydrous MgSO.sub.4. The crude yield was 15.98 g.

The material was then dissolved in 90% hexane/ethyl acetate and chromatographed on an MPLC column. Fractions containing the desired product were pooled and dried yielding 9.97 g of pure product. NMR analysis confirmed that the pure product was compound IIIc.

EXAMPLE 3

Oral Availability of Butyrate Prodrugs of Lactic Acid in Rats

We evaluated oral bioavailability and sustenance of plasma concentrations of butyric acid in rats receiving either compound IIIa, IIIb or IIIc by oral gavage at doses of approximately 3 g/kg body weight. The butyrate prodrugs were formulated by simple dilution in corn oil.

The assay was carried out according to the protocols described in Daniel et al., Clinica Chimica Acta, 181, pp. 255-64 (1989); Planchon et al., J. Pharm. Sci., 82, pp. 1046-48 (1993); Pouillart et al., J. Pharm. Sci., 81, pp. 241-44 (1992)]. Each compound was tested in five to six rats (Sprague Dawley; Harlan Labs, Inc.) weighing approximately 300 grams each. The relevant C.sub.max for these agents are listed in Table 1, below.

TABLE 1 Pharmokinetics of butyrate prodrugs of lactic acid in rats. Com- Dose No. of Butyrate Butyrate AUC pound g/kg Animals C.sub.max (.mu.M) t.sub.max (hr) (mM/hr) IIIa 2.7 4 1335 .+-. 593.2 0.56 .+-. 0.31 2.10 .+-. 0.42 IIIb 2.5 6 147.0 .+-. 119.1 0.54 .+-. 0.49 0.26 .+-. 0.14 IIIc 3.0 6 456.03 .+-. 80.7 1.71 .+-. 1.3 1.68 .+-. 0.16

These results demonstrate that the compound of this invention are able to release butyrate at a suitable rate and provide a sufficient plasma concentration of butyrate to be utilized in a treatment of .beta.-hemoglobinopathies and cancer.

EXAMPLE 4

Oral Availability of Butyrate Prodrugs of Lactic Acid in Monkeys

Compound IIIc was further tested in anemic rhesus monkeys. A single oral dose of compound IIIc (0.3, 1.0 or 3.0 g/kg body weight) diluted in corn oil was administered to the monkeys. The C.sub.max obtained at each of these doses is listed in Table II, below.

TABLE 2 Pharmacokinetic parameters for Compound IIIc in anemic rhesus monkeys. Dose No. of Butyrate C.sub.max Butyrate (g/kg) Animals (.mu.M) t.sub.max (hr) AUC (mM/hr) 0.3 2 214.4 .+-. 88.8 0.75 0.30 .+-. 0.03 1.0 2 509.9 .+-. 90.9 3.0 1.33 .+-. 0.09 3.0 2 836.1 .+-. 88.4 4.0 3.41 .+-. 0.03

The time course of plasma butyric acid concentration following administration of the various doses of compound IIIc in individual monkeys is depicted in FIG. 1.

EXAMPLE 5

Efficacy Studies of Compound IIIc/Hydroxyurea Combination in Anemic Rhesus Monkeys

The efficacy of compound IIIc administered in conjunction with hydroxyurea was tested on six anemic rhesus monkeys divided into three groups of two each. Each group was studied in two phases, as shown below. Fetal hemoglobin cells (F cells), Hemoglobin F level in total Hemoglobin (%Hb F) and %y globin chain levels were monitored before and after each of the two phases. %F cells were measured according to the protocol described in Betke et al, Blut., 4, pp. 241-9 (1958). %Hb F and %y globin chain synthesis were measured using High Performance Liquid Chromatography (HPLC) according to the protocol described in Huisman, J. Chromagtogr., 418, pp. 277 (1987).

TABLE 1 Phase I of the efficacy study. Study Number of Treatment Group Animals Drug Dose Period I 2 Hydroxyurea 50 mg/kg/day 5 weeks II 2 Compound IIIc 1 g/kg/day 5 weeks III 2 Compound IIIc 3 g/kg/day 6 weeks

TABLE 2 Phase II of the efficacy study. Study Number of Treatment Group Animals Drug Dose Period I 2 Hydroxyurea 50 mg/kg/day 5 weeks + Compound IIIc II 2 Compound IIIc 1 g/kg/TID 5 weeks III 2 Compound IIIc wash-out 4 weeks

Animal 1 in group I had a %F cell count of 8-10% before Phase I. At the end of Phase I the %F cell count in Animal 1 increased to 25%. At the end of Phase II the %F cell count in Animal 1 increased to 35%. Animal 2 in group II had a %F cell count of 8-10% before Phase I. At the end of Phase I the %F cell count in Animal 2 increased to 15%. At the end of Phase II the %F cell count in animal 2 increased to 22%. The increase in the %F cell count in Group I was accompanied by a measurable increase in the %Hb F and %y-globin chain levels. Groups II and III showed a small but significant increase in %F cells with no measurable change in HBf or Y-globin chain levels.

In all three groups, there was no detectable difference in the levels of the triglycerides and ALT prior to or during the phases of the efficacy study.

The results demonstrated the utility of the butyrate prodrugs of the present invention, when used in conjuction with conventional agents, such as hydroxyurea, for inducing fetal hemoglobin in .beta.-hemoglobinopathies.

While we have hereinbefore described a number of embodiments of this invention, it is apparent that our basic constructions can be altered to provide other embodiments which utilize the syntheses, processes and compositions of this invention. Therefore, it will be appreciated that the scope of this invention is to be defined by the claims appended hereto rather than by the specific embodiments which have been presented hereinbefore by way of example.