SYNTHESIS OF 1-OXACEPHEMS FROM D-ARABINAL AND L-RHAMNAL

Readily available from D-arabinal and L-rhamnal 2-C:1-N-carbonyl-2-deo xy-beta-D-arabino- and -alpha-L-gluco-pyranosylamines 5, 25 and 26 wer e transformed into cephems 45 and 49 via a sequence of reactions consi sting of alkylation of the beta-lactam nitrogen atom, deprotection of pyranoid hydroxy groups, glycolic cleavage of the vic diol grouping, d iscrimination of carbon atoms which were separated by periodate oxidat ion, and formation of the 1,3-oxazine six-membered ring fused to the b eta-lactam fragment. Discrimination of two aldehyde groups obtained du ring the glycolic cleavage step was achieved after their reduction and protection of one of the hydroxymethyl group by a bulky silyl substit uent or by lactonization. (C) 1997 Elsevier Science Ltd.