Conformational analysis of Amphotericin B.

Within a theoretical approach to the problem of antifungal action of Amphotericin B (AmB), a conformational analysis of the neutral and zwitterionic form of this antibiotic in vacuo was performed by the MM2P and AM1 methods. The analysis was carried out with regard to the mutual orientation of the macrolidic and glycosidic fragments of the molecule, which is defined by the phi and psi steric angles. This orientation defines the overall shape of the molecule and is postulated to be important for the antifungal action of the drug.

Cycloartane triterpene glycosides from Astragalus trigonus.

Three new cycloartane glycosides, trigonoside I, II and III, and the known astragalosides I and II were isolated from the roots of Astragalus trigonus. The structures of the new glycosides were totally elucidated by high field (600 MHz) NMR analyses as cycloastragenol-6-O-beta-xylopyranoside, cycloastragenol-3-O-[alpha-L-arabinopyranosyl(1-->2)-beta-D- xylopyranosyl]- 6-O-beta-D-xylopyranoside and cycloastragenol-3-O-[alpha-L-arabinopyranosyl (1-->2)-beta-D-(3-O-acetyl)-xylopyranosyl]-6-O-beta-D-xylopyranoside.

Stereostructure of Rimocidin.

NMR studies of rimocidin, consisting of DQF-COSY, ROESY, HSQC, HMBC and 1D-TOCSY experiments, resulted in the assignment of the absolute configuration of the rimocidin chiral centers as 2S, 3R, 9S, 11R, 13S, 14R, 15S, 17R, and 27R. The geometry of tetraene chromophore was found to be all-trans.

Stereostructure of perimycin A.

The gross structure of perimycin A was revised: the position of the keto group was changed from C-13 to C-5. The stereostructure of perimycin A was established based upon NMR studies.

Minor taxoids from Taxus wallichiana.

The needles of Taxus wallichiana afforded a new analogue of taxinine M [1a] and two derivatives of brevifoliol [2a, 3a]. The conformation of 3a was investigated by nmr spectroscopy with the aid of variable-temperature experiments and in situ reactions.