Synthesis of 3,6-Dideoxy-D-e/-yz/iro-hexos-4-ulose and Identification as the 3,6-Dideoxy-4-ketohexose from Pasteurella pseudotuberculosis Sir:The 3,6-dideoxyhexoses are biologically important carbohydrates which contribute to the serological specificity of many immunologically active lipopolysaccharides.1 Elucidation of the biochemical pathways for the formation of these sugars has been the subject of several recent investigations.2•3 Abequose (13) The authors thank Dr. T. T. Tchen and his research group for their help in the use of the Nuclear-Chicago Model Isocap/300 liquid scintillation system for the radioautography.

The synthesis of 3,6-dideoxy-1,2-0-isopropylidene-a-~-xylo-hexopyranoside (14) starting from methyl 4,6-0-benzylidene-3-deoxy-a-D-ribo-hexopyranoside (2) and from methyl 4,6-0-benzylidene-3-deoxy-a-~-rylo-hexopyranoside (16) is described. An attempt to prepare 14 by the direct isopropylidation of the known 3,6-dideoxy-Drylo-hexose (29) was unsuccessful as the major product formed in this reaction was a furanose derivative, 30. Oxidation of 14 with ruthenium tetroxide in carbon tetrachloride gave the keto sugar derivative 32 which was hydrolyzed with Dowex-50 (H+) to give 3,6-dideoxy-D-erythro-hexos-4-ulose (3,6-dideoxy-4-keto-D-glucose, l), an important intermediate in the biosynthesis of several biologically important 3,6-dideoxy hexoses. The identification of the natural product with the synthetic material 1 has already been recorded.Elucidation of the biochemical pathways for the formation of the biologically important 3,6-dideoxy hexoses, which contribute to the serological specificity of many immunologically active lipopolysaccharides,2 has been the subject of several investigation^.^^^,^ Abequose, paratose, and ascarylose were shown to originate from cytidine 5'-diphosphate-6-deoxy-4-keto-D-glucose which in turn was formed from cytidine 5'-diphosphate-D-glucose. It was established recently that 3,6-dideoxy-D-erythro-hexos-4-~1-XH OH 1 ose (1) as its cytidine diphosphate nucleotide conjugate is the intermediate between cytidine 5'-diphosphate-6-deoxy-4-keto-D-glucose and the 3,G-dideoxy hexoses in Pasteurella pseudotuberculosis type V strain VO.la7 The biological importance of this keto sugar 1 has been increased by the finding that its L isomer (3,6-dideoxy-~-erythro-hexos-4-ulose) occurs in nature as part of the antibiotic cinerubine B.8 In this paper we describe the total synthesis of the free keto sugar 1. The preparation of the a-methyl glycoside of 1 by another route was recently reported by Paulsen and c o -w~r k e r s .~ Methyl 3-deoxy-4,6-0-benzylidene-a-D-ribo-hexopyranosidel0Jl (2) was prepared according to the method of Hedgley et a1.l1 Conversion of 2 to the benzyl ether 3 fol-OCH3 7, R = CH,CtiHj 8, R = H 9, R = Ac M M e s o d OR OR CHj CHj 10, R = AC 12 11, R = H RO CHJ CHJ 13, R = COGjH, 14, R = H 15, R = Tos lowed by removal of the benzylidene protection by acid hydrolysis provided methyl 2-0-benzyl-3-deoxy-a-~-ribohexopyranoside (4). Treatment of 4 with excess of methanesulfonyl chloride in pyridine gave the dimesylate 5.Selective displacement of the primary methanesulfonate group to obtain the 6-iodo derivative 6 was achieved by the treatment of 5 with 1.1 equiv of potassium iodide in refluxing 2-butanone for 90 hr. Hydrogenation of 6 in the presence of triethylamine and 10% Pd/C using ethanol as solvent provided the 3,6-dideoxy sugar derivative, 7.As a keto sugar is usually very sensitive toward acids, it was necessary to change the protection of the hydroxyl group a t position 1 from the methyl glycoside (which requires very strong acid conditions for hydrolysis) to a group that can be e...