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

A panel of alpha-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, N-alpha-(fluoren-9-ylmethoxycarbonyl)-O-(2,3,4-tri-O-acetyl-6-axido-6-deoxy-beta-D-glucopyranosyl)-L-threonine pentafluorophenyl ester 8 and N-alpha-(fluoren-9-ylmethoxycarbonyl)-O-{2,3,4-tri-O-acetyl-6-[2'-(tert-butoxycarbonylamino)benzoylamino]-6-deoxy-beta-D-glucopyranosyl}-L-theronine pentafluorophenyl ester 9 containing the fluorogenic 2-aminobenzamide (Abz) group, have been synthesized, These compounds have been obtained by the glycosylation of N-alpha-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 a-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 alpha-helicity.