Patent ID: 8093410

Claim:
A method of obtaining a substantially diastereomerically pure composition of a compound of formula (I), comprising: crystallizing said compound of formula (I) from a mixture of diastereomers under appropriate crystallization conditions, wherein said compound of formula (I) is: wherein: z is a single or double bond, provided that when z is a double bond, X 2 is C and Y 1 is hydrogen; and provided that when z is a single bond, X 2 is CH or O; X 1 is O, S, or CN, provided that when X 1 is CN or S, X 2 is O; Y 1 is a halide, hydrogen or O-L 2 , or absent when X 2 is O; L 1 and L 2 are independently selected from hydrogen and a protecting group, or L 1 and L 2 together are a protecting group, provided that when X 1 is CN, L 1 is absent; or a salt thereof.