Patent ID: 8334398

Claim:
A process for the synthesis of a crystalline form of a compound having a structure of formula (II) or a pharmaceutically acceptable salt thereof wherein X is S or Se; W is O, S, or (R)(R), where each occurrence of R is independently H or a C 1-2 alkyl; n is 0 or 1; R 1 and R 2 are independently C 1-10 alkyl; R 3 is —H or C 0-6 alkyl-COOR 6 ; R 3′ is H, amino, cyano, halogen, aryl, aralkyl, heteroaryl, heteroaralkyl, carboxyl, C 1-10 alkyl, C 1-10 alkenyl, or C 1-10 alkynyl; R 4 is —OH, —H, —CH 3 , —OC(O)C 1-10 aralkyl, —OC(O)C 1-10 alkyl, —OC(O)aryl, or a glutamine; R 5 is —OH, cyano, C 1-10 alkoxy, amino, O-aralkyl, —OC(O)C 1-10 aralkyl, —OC(O)C 1-10 alkyl, —OC(O)aryl, or a glycine substituent; and R 6 is H or C 1-10 alkyl; wherein the melting point of the crystalline form is greater than 160° C.; comprising reacting a compound having a structure of formula (R 1 )(R 2 )AsCl wherein R 1 and R 2 are each methyl; with a compound having the structure: in an aqueous or alcoholic solvent system.