22 α(2,8)およびα(2,9)オリゴシアル酸の立体選択的合成法の開発(口頭発表の部)

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Oligo-α(2,8) and α(2,9) sialic acids 1 and 2 are located at the non-reducing end of glycoconjugates on the cell surface, and play a central role in cell surface recognition phenomena. However, the poor availability of the pure sialo-containing glycoconjugates from the natural sources makes it difficult to elucidate their biological activity. Thus, an effective methodology for the synthesis of oligosialic acids is required. However, oligosialic acids represent difficult and challenging synthetic targets. Herein, we report on the synthesis of α(2,8) and α(2,9) tetrasialic acids 24 and 32 by direct glycosidation strategy. The first approach for the synthesis of oligosialic acids involves coupling N-Troc sialyl donor 3 and acceptor 4. The building blocks were amenable to the synthesis of an α(2,8) disialic acid 5 and, however, did not enable an access to the synthesis of an α(2,8) trisialic acid 7. Next we designed the sialyl donors and acceptors containing a 5-N,4-O-carbonyl protecting group. Glycosylation of the 5-N,4-O-carbonyl protected sialyl acceptors 15a and 15d containing two hydroxyl groups at C7, 8 and C8, 9 positions with the sialyl donor 14 containing the cyclic protecting group provided α(2,8) and α(2,9) disialic acids 16a and 16d in excellent yields and selectivity, respectively. The cyclic protecting group enabled α-selective glycosidation without acetonitrile effects and was effective for improving reactivity of the C8 hydroxyl group toward glycosylation. Using the sialyl building blocks, we succeeded in the synthesis of tetra-α(2,8) and α(2,9) sialic acids 24 and 32 in high yield and selectivity.
天然有機化合物討論会の論文
2006-09-15

22 α(2,8)およびα(2,9)オリゴシアル酸の立体選択的合成法の開発(口頭発表の部)

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