A process for preparation of stable amorphous R-(+)-lansoprazole

Disclosed herein is a process for preparing stable amorphous R-(+)-Iansoprazole comprising optically resolving racemic lansoprazole by forming a reversible host-guest inclusion complex that includes a chiral guest molecule in the lansoprazole lattice comprising the following steps: (a) treating racemic lansoprazole with R-(+)-2,2'-dihydroxy-l,1'binaphthyl ("R-(+)-BINOL") in a suitable solvent to form the inclusion complex of R-(+)-lansoprazole with R-(+)-BINOL; (b) removing the inclusion complex of R-(+)-lansoprazole with R(+)-BINOL prepared in step (a) from the solvent and adding a mixture of organic solvents; (c) crystallizing the R-(+)-lansoprazole - R-(+)-BINOL inclusion complex from the mixture of organic solvents; (d) enriching the R-(+)-lansoprazole - R-(+)-BINOL inclusion complex to obtain a purity of more than about 97% e.e.; (e) cleaving the enriched R-( + )-lansoprazole inclusion complex; R-(+)BINOL (f) separating the R-BINOL and R-(+)-lansoprazole; and (g) isolating the R-(+)-lansoprazole.