orm thereof, with an appropriately substituted aldehyde or ketone; or(iv) the reaction of a compound of the formula (III): or a protected form thereof, wherein Y is a group which can be converted to an amide e.g. methyl, carboxylic acid, carboxylic ester, halide; and then converting to an amide;and thereafter removing any protecting group present;wherein X1-5, A, R1 and R2 are as defined herein; a