HYDROGEN-BONDING DONOR ACCEPTOR SCALES IN BETA-SULFONAMIDOPEPTIDES/

The conformational preferences of beta-sulfonamidopeptides in chlorofo rm solution were investigated by variable-temperature H-1 NMR spectros copy and FT-IR spectroscopy. The following hydrogen-bonding acceptor s cale was derived from the experiments: RCON approximate to tBuOCON > C OOMe greater than or equal to RSO2N. An intermolecular study gave resu lts complementary to those described above: the N-H stretch bands of N -methylacetamide and N-methyl methanesulfonamide in chloroform were fo llowed during titration with excess methanesulfonylpyrrolidine and N,N -dimethylacetamide. Shifts to lower frequencies were observed which ar e correlated with the hydrogen-bond strengths and show that the amide is a stronger hydrogen-bond acceptor than the sulfonamide.