The Molecular and Crystal Structure of tert-Butyl N.ALPHA.-tert-Butoxycarbonyl-L-(S-trityl)cysteinate and the Conformation-Stabilizing Function of Weak Intermolecular Bonding.

The title compound, C31H37NO4S [systematic name: (R)-tert-butyl-2-[(tert-butoxycarbonyl)amino]-3-(tritylsulfanyl)propanoate] is an L-cysteine derivative with three functions: NH2, COOH and SH, blocked by protecting groups tert-butoxycarbonyl, tert-butyl and trityl, respectively. The main chain of the molecule adopts the extended, nearly all-trans C5 conformation with the intramolecular N-H...O=C hydrogen bond. The urethane group is not involved in any intermolecular hydrogen bonding. Only weak intermolecular hydrogen bonds and hydrophobic contacts are observed in the crystal structure. These are C-H...O hydrogen bonds and CH/pi interactions with donor...acceptor distances, C...O ca. 3.5 A a…