5- deoxy septanoside

W. S. Fyvie, M. Morton, and M. W. Peczuh, Synthesis of 2-iodo-2-deoxy septanosides from a D-xylose-based oxepine Intramolecular cyclization in the absence of a glycosyl acceptor, Carbohydr. Res., 339 (2004) 2363-2370. 

Such cyclization methods found general utility as in the case of the preparation of nucleoside analogue 10 from an aldoheptose 8 and septanose 9, reported by Gos-selin and coworkers (Scheme 13.3a) [13]. In this instance, 5-deoxy septanoside was obtained. On the contrary, a 2-deoxy septanoside derivative was obtained by oxidation of alcohol 11, followed by oxidation to aldehyde and acid-catalyzed cyclization to afford 12 (Scheme 13.3b) [14]. 

Apart from metal-catalyzed cross-coupling reactions, hydrogenolysis of halo-oxepine was used as a key step for the synthesis of 2-chloro-2-deoxy septanoside... 

SCHEME 13.26 Synthesis of 2-chloro-2-deoxy septanoside derivative 94 [32]. 

Fig. 15. Different perspectives of the methyl 2-deoxy-a-D-g/nco-septanoside (210) structure from X-ray data.

M. E. Butcher and J. B. Lee, Seven-membered ring sugars factors influencing the formation of branched-chain 3-deoxy-3-nitro-septanosides, J. Chem. Soc., Chem. Commun. (1974) 1010-1011. 

The first report of the formation of a septanose could be traced back to the work of Micheel and Suckfiill in 1933 [7,8]. Pyranose derivative 1, upon treatment with acetic anhydride (AC2O), in the presence of pyridine, led to the formation of a/p-mixture of 6-deoxy per-O-acetyl-D-galactoseptanose 2 (Scheme 13.1a). Viability of the cyclization of acyclic precursors was reiterated further by Anet, and Stevens and coworkers for example, treatment of D-glucose with acetone in the presence of mineral acid afforded septanoside 3, although in yields less than 5% (Scheme 13.1b) [9,10]. 

An interesting observation of septanoside formation was reported by Murphy and coworkers, when studying epoxidations of 6-deoxy hex-5-enopyranosides [15]. Thus, epoxidation of 13 for a prolonged period in the presence of oxone and 1,1,1,-trifluoroacetone, followed by hydrolysis, afforded hexos-5-ulose 14, which, upon... 

SCHEME 13.4 Reactions of 6-deoxy-5-enopyranoside to prepare septanoside 16 [15],... 

Whereas cyclization of aldohexose and aldoheptose proceeded septanoside formation, implementing aldol-type condensation was also devised to derive septanoside systems. An early report by Baschang illustrated that a dialdehyde, such as 17, obtained by periodate oxidation of a pyranoside, upon Knoevenagel condensation afforded 3-deoxy-3-nitroseptanoside 18 (Scheme 13.5a) [16], On the contrary, such a reaction on dialdehyde 19 with ethyl nitroacetate afforded hij-nitro-septanoside derivatives 20 and 21 (Scheme 13.5b) [17]. 

The ring expansion of oxyglycal-derived gm-dihalo 1,2-cyclopropanate oxyglycals provides stable seven-membered halo-oxepines, that are thus suitable precursors for further functionalizations. In a study, vinyl bromide of the bromo-oxepine was used for the metal-catalyzed cross-coupling reactions, namely, Heck, Suzuki, and Sonogashira reactions, so as to generate 2-deoxy-2-C-alkyl/ary/alkynyl septanosides [33]. 

Heck and Suzuki coupling reactions with bromo-oxepine 65 afforded 2-deoxy-2-alkyl/aryl septanosides. For example, Heck reaction of 65 with acrylates and styrene led to a high yield of coupled products groups as 86, whereas the use of a-methyl styrene furnished 87, in which the exo-cyc ic double bond isomerized to a terminal double bond. Suzuki coupling reaction with substituted phenylboronic acid led to 2-deoxy-2-C-aryl septanoside derivatives 88 in good yields. On the contrary, Sonogashira coupling reaction of 65 with acetylenes furnished 2-deoxy-2-C-alkenyl septanoside 89 (Scheme 13.24). 

One of the Heck-coupled products was subjected to a hydrogenolysis (Pd/C, H2) to afford o-manno-sept-S-uloside 90. Subsequent NaBH4-mediated reduction led to hydroxyl group containing 2-deoxy-2-C-alkyl septanoside 91, in an excellent yield as a single epimer (Scheme 13.25) [33]. 

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