23 立体選択的アラビノフラノシル化反応の開発とミコバクテリア由来分岐オリゴアラビノフラノシド合成(口頭発表の部)

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Arabinofuranoside is found in the plant and mycobacterium as arabinan, whose 5-membered ring structure is absolutely different from 6-membered pyranose ring in human oligosaccharide. Its biosynthesis is the one of the new target for anti-mycobacterial agents. β-Arabinofuranoside is located at the non-reducing terminal in mycobacterial cell wall arabinan 1 (Figure 1), even though mainly α-linkage of arabinofuranosides existed in these arabinans. Because β-arabinofuranosides has a 1,2-cis stereochemistry, the synthesis of β-arabinoluranosidic linkage is troublesome compared to that of α-isomer. Here, we wish to report 1) the effect of protections of glycosyl donors on the stereoselectivity of arabinofuranosylation and 2) the synthesis of the terminal hepta-arabinofuranoside of mycobacteral arabinan 1. 1) Development of stereoselective arabinofuranosylation First of all, we examined the β-selective glycosylation of perbenzyl-d_7 protected arabinofuranosyl donor using our novel methodology for high-throughput screenings (HTS) of O-glycosylation conditions (Figure 1). However β-selectivity could not be improved from 〜110 screenings examined on the effect of solvent and temperature (Scheme 1). So, we synthesized several donors with various non-participating protections possibly existing in different shape. Both α- and β-stereoselective arabinofuranosylations were achieved only by changing of the protection of donor (Table 1, 2). The combibation of 3,5-tetraisopropyldisiloxanylidene protected arabinofuranosyl donor (2i, 2j) with the matched acceptor 3 gave β-isomer predominantly (Table 3). 2) Synthesis of branched heptaarabinofuranoside 1 of mycohacterial cell wall arabinan For the synthesis of 1, we designed the matched pentaarabinofuranoside acceptor 11, which was prepared from methyl α-D-arabinofuranoside through the double α-arabinofuranosylation of trisaccharide 9. Double β-arabinofuranosylation of 9 with the donor 2i was achieved stereoselectively to give heptaarabinofuranoside derivative 12, which was deprotected as usual to give the target branched oligoarabinofuranoside 1 (Scheme 2).
天然有機化合物討論会の論文
2005-09-15

23 立体選択的アラビノフラノシル化反応の開発とミコバクテリア由来分岐オリゴアラビノフラノシド合成(口頭発表の部)

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