Murolic acid

T. Flezanka and I. A. Gushina, Glycosidic compounds of murohc, protoconstipatic and allo-murolic acids from lichens of Central Asia, Phytochemistry, 54 (2000) 635-645. 

Murolic acid, M-10093 Neuropogolic acid, in 1-10037 Pregnane-3,8,14,17,20-pentol, P-30118 Pregnane-3,12,14,17,20-pentol, P-10138... 

Deriv Isomurolic acid, mp 115-116 °C (MeOH), by heating of murolic acid in dimethyl-formamide at 150 °C for 30 min StL Lecanora muralis (Schreb.) Rabenh. 

The configuration of ( + )-murolic acid (53) was determined in the following manner (7P2). The H-n.m.r. spectrum of (53) exhibited /3 4 of 6 Hz comparable with that of (+ )-protolichesterinic acid (62), thus establishing a raii -relationship of these protons. Rearrangement of (53) by treatment with acetic anhydride and pyridine produced (+ )-acetylisomur-olic acid (63). The CD curve of this compound was compared with that of the 4(S)-lactone (64) and shown to have the opposite configuration at C-4, i.e. 4(R). Hence from the H-n.m.r. studies, ( + )-murolic acid (53) must have the 3( S), 4(R) configuration shown. 

The relative configuration of (+ )-neodihydromurolic acid (54) similarly followed from the H-n.m.r. spectrum and was shown to be trans, trans ( 3 2 = 11 Hz, /3 4 = 9Hz). Catalytic hydrogenation of ( + )-murolic acid (53) gave a mixture of isomurolic acid (65) and dihydromurolic acid (66). Subsequent esterification and equilibration with sodium methoxide gave methyl neodihydromurolate (67) thus confirming that (53) and (54) must have the same configuration at C-18, C-4 and C-3 (Scheme 8). 

Scheme 8. Correlation of the structure of murolic acid and neodihydromurolic acid...

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