Branched-chain sugars. Part 18. Syntheses of D-rubranitrose (2,3,6-trideoxy-3-C-methyl-4-O-methyl-3-nitro-D-xylo-hexopyranose) and a derivative of D-kijanose (2,3,4,6-tetradeoxy-4-methoxycarbonylamino-3-methyl-3-nitro-α-D-xylo-hexopyranose)

Abstract

D-Rubranitrose (2,3,6-trideoxy-3-C-methyl-4-O-methyl-3-nitro-D-xylo-hexopyranose)(22), a constituent of the antibiotic rubradirin, has been synthesized from methyl 3,3¹-anhydro-[4,6-O-benzylidene-2-deoxy-3-C-(hydroxymethyl)-α-D-arabino-hexopyranoside](8) in a stereochemically defined manner. A key sequence in the synthesis involved the conversion of the epoxide (8) into methyl 3-amino-4,6-O-benzylidene-2,3-dideoxy-3-C-methyl-α-D-ribo-hexopyranoside (12). The latter compound was then transformed in a straightforward manner into methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-α-D-ribo-hexopyranoside (17), which was converted into D-rubranitrose (22) by a sequence of reactions identical to that used previously in the L-series.

Forthe synthesis of methyl α-D-kijanoside (methyl 2,3,4,6-tetradeoxy-4-methoxycarbonylamino-3-C-methyl-3-nitro-α-D-xylo-hexopyranoside)(36), a derivative of a configurationally related methyl-branched nitro sugar from the antitumour antibiotics kijanimicin and tetrocarcins A and B, methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-α-D-xylo-hexopyranoside (19), an advanced intermediate in the synthesis of D-rubranitrose, was transformed into the corresponding N-trifluoroacetyl derivative (29), mesylation of which gave methyl 2,3,6-trideoxy-3-C-methyl-4-O-methylsulphonyl-3-trifluoroacetamido-α-D-xylo-hexopyranoside (32). Treatment of the latter compound with sodium borohydride in ethanol furnished methyl 2,3,4,6-tetradeoxy-3,4-epimino-3-C-methyl-α-D-ribo-hexopyranoside (33), which, on ring-opening with azide ion, produced a separable mixture of methyl 3-amino-4-azido-2,3,4,6-tetradeoxy-3-C-methyl-α-D-xylo-hexopyranoside (34) and its regioisomer (35). The conversion of compound (34) into methyl α-D-kijanoside (36) has already been described.