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Nucleophilic displacements of methyl 2,3-O-isopropylidene-4-O-toluene-p-sulphonyl-α-d-lyxo- and -β-l-ribo-pyranosides, and deamination of the corresponding 4-amino sugars

1976; Elsevier BV; Volume: 52; Issue: 1 Linguagem: Inglês

10.1016/s0008-6215(00)85944-3

1873-426X

J. S. Brimacombe, Jonathan Minshall, Leslie C.N. Tucker,

Click Chemistry and Applications

Reinvestigation of the reaction of methyl 2,3-O-isopropylidene-4-O-toluene-p-sulphonyl-α-d-lyxopyranoside (4) with azide ion has shown that methyl 4-deoxy-2,3-O-isopropylidene-β-l-erythro-pent-4-enopyranoside (8, ∼51.5%) is formed, as well as the azido sugar 7 (∼48.5%) of an SN2 displacement. The unsaturated sugar 8 was more conveniently prepared by heating the sulphonate 4 with 1,5-diazabicyclo-[5.4.0]undec-5-ene. An azide displacement on methyl 2,3-O-isopropylidene-4-O-toluene-p-sulphonyl-β-l-ribopyranoside (12) furnished methyl 4-azido-4-deoxy-2,3-O-isopropylidene-α-d-lyxopyranoside (13, ∼66%) and the unsaturated sugar 14 (∼28.5%), which was also prepared by heating the sulphonate with 1,5-diazabicyclo[5.4.0]undec-5-ene. Deamination of methyl 4-amino-4-deoxy-2,3-O-isopropylidene-α-d-lyxopyranoside (5), prepared by reduction of 13, with sodium nitrite in 90% acetic acid at ∼0°, yielded methyl 2,3-O-isopropylidene-α-d-lyxopyranoside (10a, 26.2%), methyl 2,3-O-isopropylidene-β-l-ribofuranoside (21a, 18.4%), and the corresponding acetates 10b (34.5%) and 21b (21.3%). These products are considered to arise by solvolysis of the bicyclic oxonium ion 29, formed as a consequence of participation by the ring-oxygen atom in the deamination reaction. Similar deamination of methyl 4-amino-4-deoxy-2,3-O-isopropylidene-β-l-ribopyranoside (6) afforded, exclusively, the products 10a (34.4%) and 10b (65.6%) of inverted configuration. Deamination of methyl 5-amino-5-deoxy-2,3-O-isopropylidene-β-d-ribofuranoside (20) gave 22ab, but no other products. An alternative synthesis of the amino sugars 5 and 6 is available by conversion of 10a into methyl 2,3-O-isopropylidene-β-l-erythro-pentopyranosid-4-ulose (11), followed by reduction of the derived oxime 15 with lithium aluminium hydride.