Linarinic acid, (-)-1,2,3,9-tetrahydropyrrolo[2,1-b]quinazoline-1-carboxylic acid (4a), was isolated from the ethanol extract of Linaria vulgaris Mill. In our previous study, a series of tetrahydropyrrolo[2,1-b]quinazoline derivatives 4b, 4c, 5a, 5b, 6a and 6b that were structurally related to 4a