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. 2014 Jun 6;79(11):4878-91.
doi: 10.1021/jo500449h. Epub 2014 May 12.

Synthesis and reactivity of 4'-deoxypentenosyl disaccharides

Panuwat Padungros  1 , Ren-Hua Fan, Matthew D Casselman, Gang Cheng, Hari R Khatri, Alexander Wei
Affiliations

Synthesis and reactivity of 4'-deoxypentenosyl disaccharides

Panuwat Padungros et al. J Org Chem. .

Abstract

4-Deoxypentenosides (4-DPs) are versatile synthons for rare or higher-order pyranosides, and they provide an entry for structural diversification at the C5 position. Previous studies have shown that 4-DPs undergo stereocontrolled DMDO oxidation; subsequent epoxide ring-openings with various nucleophiles can proceed with both anti or syn selectivity. Here, we report the synthesis of α- and β-linked 4'-deoxypentenosyl (4'-DP) disaccharides, and we investigate their post-glycosylational C5' additions using the DMDO oxidation/ring-opening sequence. The α-linked 4'-DP disaccharides were synthesized by coupling thiophenyl 4-DP donors with glycosyl acceptors using BSP/Tf2O activation, whereas β-linked 4'-DP disaccharides were generated by the decarboxylative elimination of glucuronyl disaccharides under microwave conditions. Both α- and β-linked 4'-DP disaccharides could be epoxidized with high stereoselectivity using DMDO. In some cases, the α-epoxypentenosides could be successfully converted into terminal l-iduronic acids via the syn addition of 2-furylzinc bromide. These studies support a novel approach to oligosaccharide synthesis, in which the stereochemical configuration of the terminal 4'-DP unit is established at a post-glycosylative stage.

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Figures

Figure 1
Figure 1
Post-glycosylative approach toward 1,4-linked disaccharides with diverse terminal sugars derived from 4′-deoxypentenosyl disaccharides.
Scheme 1
Scheme 1. Synthesis of β-Thiophenyl 4-DP Donor 2
Scheme 2
Scheme 2. Synthesis of α-Thiophenyl 4-DP Donor 5
Figure 2
Figure 2
NOE interaction between H1′ and H4 in 7.
Figure 3
Figure 3
LUMO of “unsaturated” 4-DP oxocarbenium (left) and “saturated” dihydro analogue (right). The enol ether in the former affects the capacity of the O5 oxygen lone pair to stabilize the C1 carbenium.
Scheme 3
Scheme 3. Synthesis of β-1,4-Linked 4′-DP Disaccharide 19
Scheme 4
Scheme 4. Synthesis of β-1,4-Linked 4′-DP Disaccharide 24
Scheme 5
Scheme 5. Post-Glycosylative Modification of α-1,4-Linked 4′-DP Disaccharides 7 and 9
Scheme 6
Scheme 6. Post-Glycosylative Modification of β-1,4-Linked 4′-DP Disaccharides
Scheme 7
Scheme 7. Synthesis of l-Idopyranosides by syn-Selective C5′ Addition
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