Synthesis of chirally deuteriated (S-adenosyl-S-methylsulfonio)propylamines and spermidines. Elucidation of the stereochemical course of putrescine aminopropyltransferase (spermidine synthase)

The stereochemical course of enzyme-catalyzed aminopropyl transfer has been investigated. The stereospecific synthesis of chirally deuteriated (S-adenosyl-S-methylsulfonio)propylamines and several chirally deuteriated spermidine (-)-camphanamide derivatives has allowed the elucidation of aminopropyltransferase stereochemistry by using /sup 1/H NMR techniques. Putrescine aminopropyltransferase (spermidine synthase) isolated from Eschierchia coli catalyzed the synthesis of chirally deuteriated spermidines from 1,4-diaminobutane (putrescine) and chirally deuteriated (S-adenosyl-S-methylsulfonio)propylamines. Derivatization of the biosynthetic spermidines to 1,8-bis(Boc)spermidine (-)-camphanamides and comparison of their /sup 1/H NMR spectra with those of the synthetic standards permits determination of the absolute configuration of the biosynthetic products. The results show that the reaction catalyzed by E. coli spermidine synthase proceeds with inversion of configuration at the methylene carbon undergoing nucleophilic attack by putrescine. These data support a single-displacement mechanism proceeding via a ternary complex of enzyme and both substrates. 42 references, 5 figures.