A process for the preparation of a compound of the formula or a pharmaceutically acceptable salt thereof wherein R1 represents in which r represents 2, s represents 2 and t represents 0; R2 is group OR4, where R4 is hydrogen, C1-4 alkyl, C2-4 alkenyl or C2-4 alkynyl or R2 is a group OC(O)R5 where R5 is hydrogen or R4; and R3 is CN; said process comprising reacting a compound of the formula wherein R1( is R1 or a group convertible thereto, and R3( is CN, with a source of nitrous acid, and thereafter optionally or as necessary converting the resulting -NOH group to other -NR2 wherein R2 is as defined in formula (I), converting R1( when other than R1 to R1 and thereafter optionally forming a salt, provided that when R2 is other than OH, the salt is a pharmaceutically acceptable salt. Claimed as new is the crystalline 258 י" ג בתמוז התש" ס - July 16, 2000
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