PREPARATION OF OXAZOLIDINE-CONTAINING PEPTIDES - UNUSUAL EFFECTS IN RH-III-CATALYZED ACETALIZATIONS OF ALDEHYDES WITH URETHANE-PROTECTED SERINE AND THREONINE ESTERS AND WITH DIPEPTIDES CONTAINING SERINE OR THREONINE RESIDUES AT THE N-TERMINUS

The cyclization reaction of aldehydes with Z- and Boc-protected beta-hydroxyamino-acid esters (Tables 1 and 2), or of dipeptides containing serine or threonine at the N-terminus (Table 3), to give oxazolidine derivatives, occurs in the presence of isopropyl orthoformate and catalytic amounts of [Rh(MeCN)(3)(triphos)] (CF3SO3)3 The reaction may be carried out under kinetic or under thermodynamic control, so that the ratio of the two possible epimeric products can be changed. The protecting group can be removed from the 3-position of the oxazolidine ring, and the resulting NH group can be coupled with another amino acid. Thus, a new method for the preparation of peptides containing beta-hydroxy-amino acid-derived oxazolidines ('pseudo-prolines') is available. N-Neopentyl-substituted tripeptides are also described.