Synthesis of 3-Substituted Xylopyrnosides from 2,3-Anhydropentosides

Abstract

The facile regio- and stereoselective epoxide ring-opening of anhydropentosides described herein provides an attractive pathway to 3-substituted analogs of pentosides. Benzyl 2,3-anhydro-β-D-ribopyranoside (2) and benzyl 2,3-anhydro-β-L-ribopyranoside (7) were obtained from benzyl β-D-arabinopyranoside (1) and benzyl β-L-arabinopyranoside (3) respectively. The anhydropentosides were converted to the corresponding new 3-amino derivatives (8, 9, 10, and 11), alkoxy derivatives (12, 13, and 14), and deoxy sugar (15) in high yield. Every conversion was a one-step reaction of the anhydroglycoside with the appropriate nucleophile. Side-products due to epoxide migration were not observed.

Notes

The Waters Sep-Pak Vac 35cc C18–10g was washed with 100 mL of methanol followed by 100 mL water to equilibrate it. Water (100 mL) was added to the reaction mixture. The solution was loaded on the cartridge, and the cartridge washed sequentially with (100 mL) of each of the following solutions: 100% water and increasing amounts of methanol (5%, 10%, 50% and 100%). The majority of the product eluted with the 50% methanol in water.

¹H-¹H COSY NMR spectra of benzyl 3-O-methyl-β-L-xylopyranoside 13 in DMSO and DMSO-D₂O were ran as an example to prove the regiochemistry. Analysis of the spectra showed that H-1 at δ 4.25 (d, J = 7.51 Hz) was coupled to H-2 at δ 3.15 (ddd, J = 8.80 Hz, 7.51 Hz, 6.41 Hz) which was in turn coupled to H-3 at δ 2.90 (t, J = 8.80 Hz, 8.84 Hz) and 2-OH at δ 5.15 (d, J = 6.41 Hz) indicating that -OCH₃ is at postion 3.

Prolonged refluxing produced a dark mixture from which isolation of the desired product was difficult.