Rapid and efficient preparative purification of building blocks suitable for solid-phase synthesis of neoglycopeptides: Synthesis and purification of O-(2,3,4,6-tetra-O-acetyl-β-d- galactopyranosyl/glucopyranosyl)-N ^α-fluoren-9-yl- methoxycarbonyl-hydroxyproline

Summary

As part of scaling-up studies for the preparation of antinociceptive neoglycopeptides, the purification of appropriate glycosylated building blocks has been optimized. The synthesis and purification of O-(2,3,4,6,-tetra-O-acetyl-β- d-galactopyranosyl/glucopyranosyl)-N ^α-fluoren-9-yl-methoxycarbonyl-hydroxyproline is described in this paper. The building blocks, suitable for solid-phase synthesis, are obtained in a single chemical step from partially protected hydroxyproline, followed by a rapid and efficient preparative purification. Preparative reversed-phase HPLC conditions have been adjusted to maximize recoveries, while reducing both time and costs of consumables. For the galactosyl conjugate, up to 0.5 g of pure lyophilized building block was obtained from 1.5 g of a crude reaction mixture using plain deionized water and less than 2 l of preparative-grade CH₃CN. The glucosyl derivative was even more efficiently purified by spontaneous after-column crystallization from the elution mixture.