Synthesis of carriers of differing Stokes radius with activated acyl groups for use as reagents in labeling membrane proteins.

Compounds with the general formula C(CH2CO--(Pro)n--R1--O--COR2)4 have been synthesized with n = 0, 1, 3, 5. The R1 alcohol group provides an active ester of the acylating function R2CO--. On reaction with a nucleophile the acyl group is attached while the major part of the reagent serves as the leaving group. Even with compounds of relatively low molecular weight the extended structures represent molecules with a substantial Stokes radius. These reagents are intended to probe the accessibility of functional groups in cell organelles, particularly membranes. Subtle differences in labeling patterns have been observed in preliminary experiments with red cell ghosts.U