Internally quenched fluorogenic, α-helical dimeric peptides and glycopeptides for the evaluation of the effect of glycosylation on the conformation of peptides

Abstract

A panel of α-helical, dimeric coiled-coil peptides has been designed and synthesized for the evaluation of the effect of glycosylation on the conformation of these coiled-coil peptides. Two glycosylated building blocks, Nα -(fluoren-9-ylmethoxycarbonyl)-O-(2,3,4-tri- O-acetyl-6-azido-6-deoxy-β-D -glucopyranosyl)-L-threonine pentafluorophenyl ester 8 and Nα -(fluoren-9-ylmethoxycarbonyl)-O-{2,3,4-tri- O-acetyl-6-[2′-(tert -butoxycarbonylamino)benzoylamino]-6-deoxy-β-D -glucopyranosyl}-L-threonine pentafluorophenyl ester 9 containing the fluorogenic 2-aminobenzamide (Abz) group, have been synthesized. These compounds have been obtained by the glycosylation of Nα-Fmoc-Thr-OPfp with the corresponding glycosyl trichloroacetimidate donors and have been incorporated into the solid-phase synthesis of the peptides 1–3 and 7 and glycopeptides 4–6. Compounds 1 and 4–7 have been synthesized as internally quenched fluorogenic compounds where the Abz group has been employed as the fluorogenic probe and 3-nitrotyrosine Tyr(NO2) as the quenching chromophore. Steady-state fluorescence studies have provided evidence to support the dimerization of the α-helical peptides. Denaturation studies, by fluorescence as well as CD spectroscopy, indicate that the introduction of a carbohydrate moiety into the coiled-coil peptides has a significant destabilizing effect on the α-helicity.