Universidad de Granada
Facultad de Ciencias



Abstract: (Chemical Abstract 2001, 134: 71727)


Different lipase enzymes have been tested in order to perform regioselective acetylations on the eudesmane tetrol from vulgarin. High yields (95%) of 1,12-diacetoxy derivative (4) were achieved in one hour with Candida antarctica lipase (CAL). However, only the 12-acetyl derivative (6) was obtained in similar yield with Mucor miehei (MML) or Candida cylindracea (CCL) lipases. The enzymatic protection at C-1 and C-12 has been used to form eudesmane cyclic-sulfites between C-6 and C-4 atoms. The R/S-sulfur configuration has been assigned by means of the experimental and theoretical 13C and 1H NMR chemical shifts. The theoretical shifts were calculated using the GIAO method, with a MM+ geometry optimization followed by a single-point calculation at the B3LYP/6-31G* level (B3LYP/6-31G*//MM+). Moreover, B3LYP/6-31G* geometry optimizations were carried out to test the B3LYP/6-31G*//MM+ results, for the deacetylated sulfites (12 and 15). In addition to the dC and dH shifts, the 3JHH coupling constants were also calculated and compared with the experimental values when available. Finally, different reactivities have been checked in both sulfites by biotransformation with Rhizopus nigricans. While the R-sulfite gave 2a- and 11b-hydroxylated metabolites, the S-sulfite yielded only regioselective deacetylations. Furthermore, both sulfites showed different reactivities in redox processes.

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