Six pentacyclic triterpene acids, ursolic acid, oleanolic acid, betulinic acid, 23-hydroxybetulinic acid, glycyrrhetinic acid, and senegenin, were metabolized by the microbe Nocardia sp. NRRL 5646 to selectively furnish their corresponding 28-methyl esters. Notably, ursolic acid (1) was converted to oleanolic acid methyl ester (4) via two intermediates, oleanolic acid (2), and ursolic acid methyl ester (3), which are formed by participation of retro-biosynthetic methyl migration from C-19 to C-20. Senegenin (11) was selectively converted to a nortriterpene methyl ester, senegenic acid methyl ester (12), via an unprecedented C-C bond cleavage. The stereochemical assignments of compounds 11 and 12 were made unambiguously for the first time using 2D NMRspectroscopy.

In a continuation of phytochemical studies on the underground organs of Liriope spicata var. prolifera, four new steroidal glycosides, lirioproliosides A-D, along with two known compounds, 25(S)-ruscogenin 1-O-[a-L-rhamnopyranosyl(1→2)[fl-D-xylopyranosyl(1→3)]-fl-D-fucopyranoside and ophiopogonin A, were identified. The structures of lirioproliosides A-D were established by a combination of spectroscopic and chemical methods as 25(S)-ruscogenin 1-O-[a-L-rhamnopyranosyl(1→2)][fl-D-xylopyranosyl(1→3)]-fl-D-fucopyranoside-3-O-a-L-rhamnopyranoside, 25(S)-ruscogenin 1-O-[3-O-acetyl-a-L-rhamnopyranosyl(1→2)]-fl-D-fucopyranoside, 25(S)-ruscogenin (1-O-[2-O-acetyl-a-L-rhamnopyranosyl(1→3)]-fl-D-fucopyranoside and ruscogenin (1-O-[2-Oacetyl-β-L-rhamnopyranosyl(1→2)]-fl-D-fucopyranoside, respectively. Among these steroidal glycosides, ophiopogonin A and lirioprolioside B, and lirioproliosides C and D, were isolated as epimeric pairs. Copyright