Abstract: The present invention relates to a process for preparing (2R,3S)-1-halo-2-hydroxy-3-(protected)amino-4-substituted butane comprising contacting a mutagenized Rhodococcus erythropolis having ATCC deposit no. PTA-6648 with (3S)-1-halo-2-oxo-3-(protected)amino-4-substituted butane substrate. The present invention also relates to a process comprising mixing (2R,3S)-1-halo-2-hydroxy-3-(protected)amino-4-substituted butane with at least one base in the presence of at least one solvent to produce a reaction mixture containing (2R,3S)-1,2-epoxy-3-(protected)amino-4-substituted butane. The present invention further relates to a process comprising crystallizing the (2R,3S)-1,2-epoxy-3-(protected)amino-4-substituted butane out of the reaction mixture by concurrently adding water and the reaction mixture together. The present invention is also directed to a mutagenized Rhodococcus erythropolis having ATCC deposit no. PTA-6648.

Abstract: A process for preparing a compound of Formula (3) in which R.sup.2 is --H; ##STR1## which comprises the steps: i) conversion of a compound of Formula (1) into a compound of Formula (2) using a dioxygenase enzyme; ##STR2## ii) conversion of the compound of Formula (2) into a compound of Formula (3) wherein is --COR; andiii) conversion of the compound of Formula (3) in which R.sup.2 is --COR into a compound of Formula (3) in which R.sup.2 is --H;wherein R.sup.2, a, b, c, d, Z, m and X are as defined in claim 1.Also claimed are individual steps of the process and new compounds of Formula (2).