Chenodeoxycholic acid (0.5 g, 1.3 mmol) in THF (10 ml) at 0° C. was treated dropwise with freshly prepared diazomethane in ether (prepared in the usual manner from diazald) until the yellow colour persisted. After 15 minutes at 0° C. the solvent was evaporated to yield a white foam (0.55 g). The compound would not recrystallise, although gas chromatography showed the product to be 97% pure. The product was further purified by preparative silica tlc. (solvent system: EtOAc/CH2Cl2 /AcOH--10:10:1) to afford pure methyl chenodeoxycholate3 (0.42 g, 81%) as a foam: 1H NMR (60 MHz; CDCl3) δ0.65 (3H, s, 18-CH3), 0.91 (3H, s, 19-CH3), 1.85 (2H, s [exchanges on adding D2O], 3α and 7α OH's), 3.1-3.7 (1H, m, 3β-H), 3.64 (3H, s, --OMe), 3.7-3.9 (1H, m, 7β-H); IR (nujol mull) 3384 (OH's), 1740 (C=O) cm-1 ; MS: Found m/z 406.3077; C25H42O4 (M) requires 406.3083.
