Pillaromycin-A: structural and synthetic studies related to the sugar moiety, pillarose

The photo-induced alkylation of enone 6 with ethylene glycol gave an adduct from which the α- D -threo ( 16 ) and α- D -erythro ( 17 ) modifications of structure 2 have been elaborated. It was thereby shown that 2 is not the structure of pillarose. Addition of vinyl magnesium bromide to the ketone 24 b gave a slight excess of one allylic alcohol, 25 , which upon treatment with osmium tetroxide and hydrogen peroxide gave directly the α,α′-ketodiol 3 a. The epimer of the latter 33 b was available via carboxymethylenation of ketone 24 b, reduction of ester, and hydroxylation. Benzoylation of these epimers gave 3 b and 33 c respectively and it was concluded that the former, methyl 2,3,6-trideoxy-4-C-[oxo(benzoyloxymethyl)methyl]-α- D -threo-hexopyranoside, 3 b, is the enantiomer of the "methyl 8-O-benzoyl pillaroside" obtained from the antibiotic pillaromycin A.