Seven zizyphine A-type cyclopeptide alkaloids were isolated from the roots of Paliurus ramossisimus by the combination of centrifugal partition chromatography and conventional separation methods. The novel structures of paliurines A-F (1-6) were characterized and established on the basis of MS and elaborate NMR spectral analyses. Terminal dipeptide stereochemistry was confirmed by correlation with the synthetic dipeptides via comparison of their (13)C NMR data.

Incubation of 8a,9ot-epoxytetrahydrolanosterol [3] with Mycobacterium sp. gave 20(5)-hydroxymethyl-12a-hydroxypregn-4-en-3-one [4] and 20(5)hydroxymethyl-4,4,14a-trimethylpregna-7,9( 11 )-dien-3ß-ol [5] in 5.0% and 1.6% yields, respectively. Incubation of lanosta-7,9(l l)-dien-3P-ol [6] resulted in the isolation of two C-19 steroids as the major metabolites that have been isolated previously from the incubation of lanosterol, and methyl 12a-hydroxybisnorchola-4,17(20)-dien-22-oate [91 in low yield. These results indicated that this microorganism is capable of carrying out saturation of a C=C bond, methylation of a carboxyl function, and 12a-hydroxylation in the steroid nucleus, besides earlier reported transformations.In previous reports we have disclosed that cycloartenol and 24-methylenecycloartanol are transformed by Mycobacterium sp. (NRRL B-3805) to give androsta-4,8( 14)-diene-3,17-dione {1} as the major metabolite, in 34 and 35% yields, respectively (1,2). It was also shown that when lanosterol [2] was incubated with this microorganism 1 was isolated as the major product in 30% yield. During this transformation, a series of complicated chemical changes occurred including demethylation at the 4 ,4ß-and 14apositions, formation of a 8<14> double bond accompanied by the disappearance of the Am> double bond, and cleavage of the C-17 side-chain. Among these changes, we were particularly interested in the disappearance of the 8*" double bond accompanied by the formation of the 8<14> double bond in 1. Therefore, lanosterol derivatives with substituent modification at C-8 and C-9 were prepared and subjected to transformation with this microorganism. RESULTS AND DISCUSSIONAfter unsuccessful attempts in hydrogenating the Am) double bond, 2 was converted smoothly with catalytic hydrogenation (H2-Pd) and peroxidation (wz-CPBA) to 8a,9a-epoxy-tetrahydrolanosterol [31 (3). Compound 3 showed a molecular ion at m!z 444 in its eims corresponding to a formula of C30H52O2. The presence of two oxygenated quaternary carbon signals at 70.6 and 68.2, along with the disappearance of two olefinic carbon signals (C-8 and C-9, overlapping at 134.5 in dihydrolanosterol) confirmed its structure. The favored -side attack by w-CPBA was confirmed by an nOe nmr study, in which a critical observation was the interaction of H-18 and H-19, which is only possible for an 8a,9a-epoxy structure in 3.From the incubation mixture of 3 with Mycobacterium sp. (NRRL B-3805), compounds 4 and 5 were isolated in relatively low yields of 5.0% and 1.6%, respectively (Scheme 1).The hreims of 4 showed a molecular ion at mlz 346.2510, consistent with an elemental formula of C^H^O^T he *H-nmr spectrum showed an olefinic proton signal at 5.70 (br s), typical for H-4 in a 3-one-4-ene sterol. The presence of this functionality was confirmed by an ir absorption at 1659 cm-1 and the uv absorption maximum at 242 nm. The ir spectrum also indicated the presence of hydroxy groups (3425 cm '). Three methyl signals in the 'H-nmr spectrum of 4 including two singlets ( 0.7...

Ceanothic acid (1) is the major triterpene isolated from Parliurus ramosissitnus (Rhamnaceae) which possesses three methyl groups corresponding to the 4,4,14α‐trimethyl groups in lanosterol (5). Microbial transformation of 1 and its 3‐dehydro‐2,28‐dimethyl ester derivative (3) with Mycobacterium sp. (NRRL B‐3805) resulted in the methylation of the carboxylic functions and C‐1 epimerization, respectively. Although this work indicates that 1 is not a suitable substrate for 4,4,14α‐tridemethylation, esterification of the carboxylic function and the C‐1 epimerization reaction in ceanothic acid and its derivative is the first observation with this microorganism.

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