An X-ray crystallographic study on 4"-0-(4-iodobenzoyl)megalomicin A has led to the revision of the structures of the megalomicins and the XK-41 antibiotics. Crystals are orthorhombic, space groupP2,2,2, with a = 12.669(2), b = 19.501 (6), c = 25.741 (9) A, and Z = 4. The structure was solved by the heavy-atom technique, and 1 812 observed reflections led to a final R of 0.095. The novel amino-sugar previously thought to be D-rhodosamine has been shown to have the L-configuration and is therefore renamed L-megosamine. It has also been shown to be glycosidically attached to the tertiary 6-hydroxy group. The 13C n.m.r. and circular dichroism (c.d.) parameters of these macrolides are described. The syntheses of methyl aand P-D-rhodosaminide, methyl aand P-D-megosaminide, methyl a-and 6-L-megosaminide, methyl a-and (3-D-angolosaminide, and methyl 2,3,6-trideoxy-3-(dimethylamino) -a-D-xylo-hexopyranoside are described and their conformations and 13C n.m.r. parameters are discussed. Methyl a-D-and -L-amicetoside, methyl a-D-and -L-cineruloside and other model 4-oxopyranosides and pyrans have been synthesized. Their c.d. properties have been determined and they have been shown to exhibit Anti-Octant behaviour.

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Configurationally different 3-azido-2,3-dideoxy-2-fluoro and 2-azido-2,3-dideoxy-3-fluoro sugars, synthetic precursors of biologically important fluoro amino acids, were synthesized. Axial alcohols involved in vicinal diaxial systems undergo fluorodehydroxylation with configurational retention in the presence of (diethylamino)sulfur trifluoride.

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