Toward <scp>l</scp>-Homo-DNA: Stereoselective de Novo Synthesis of β-<scp>l</scp>-<i>erythro</i>-Hexopyranosyl Nucleosides
作者:Daniele D’Alonzo、Annalisa Guaragna、Arthur Van Aerschot、Piet Herdewijn、Giovanni Palumbo
DOI:10.1021/jo100691y
日期:2010.10.1
A novel route to 2′,3′-dideoxy-β-l-erythro-hexopyranosyl nucleosides equipped with a 1′-(N6-benzoyladenin-9-yl) or a 1′-(thymin-1-yl) moiety has been developed. Synthesis of the enantiopure sugar moiety was carried out by a de novo approach based on a domino reaction as the key step. N-Glycosidation was explored via either nucleobase-transfer mechanism (B = T) or in situ anomerization (B = A or T)
An efficient and general de novo synthetic route to enantiomerically pure L-hexoses has been accomplished starting from the heterocyclic homologating agent 5,6-dihydro-1,4-dithiin-2-yl[(4-methoxybentyl)oxy]methane and methyl alpha,beta-isopropylidene-L-glycerate. The sugar scaffold was constructed by an acid-catalyzed domino reaction, which enabled selective preparation of either methyl 2,3-dideoxy-alpha-L-threohex-2-enopyranosides or 1,6-anhydro-2,3-dideoxy-beta-L-threo-hex-2-enopyranose as key intermediates. The subsequent double bond functionalization by syn or anti dihydroxylation reactions allowed introduction of the remaining stereogenic centers, leading to desired orthogonally protected L-hexopyranosides with a high degree of diastereoselectivity and with very good overall yields. These and previous results (based on the use of the corresponding L-erythro epimers) contribute to make our approach general and place it among the few methods able to synthesize the whole series of the rare L-hexoses.