Genuine saponins of Solidago virgaurea L., Heteropappus altaicus (Willd.) Novopokr., Heteropappus biennis (Ldb.) Tamamsch. and Helianthus annuus L. (Asteraceae) as well as related carbohydrate modified glycosides of polygalacic acid and echinocystic acid and some commercial available triterpenoid