| Abstract: |
The core trisaccharide regions of esperamicin and the aryltetrasaccharide region of calicheamicin have been synthesized. The minimum protection modalities necessary to stabilize structures against rearrangement to an isomeric azafuranose series were ascertained (see compounds 12 and 65). Deprotection of the 2-(trimethylsilyl)-ethoxycarbonyl carbamate from 65 led to azafuranose 14 characterized as methyl glycoside 15. Using this insight, it was possible to fashion, for the first time, a pre-glycosyl donor (see compound 128) corresponding to the complete arylsaccharide sector of calicheamicin γ1 1 at the oxidation level of the domain. Among the key assembly strategies were the conversion of a-thiophenylpseudoglycals to allal derivatives (see 44 → 45); the interfacing of epoxide-mediated glycosylation with iodoglycosylation (see 30 → 47 → 48); the synthesis of hydroxylamine glycosides via triflate displacement (see 61 + 91 → 101); and a new route to p-hydroxybenzonitriles (see formation of 86). © 1995, American Chemical Society. All rights reserved. |
