Abstract: A process for preparing a protected amidine group of formula (I): wherein R6 represents, for example, C1-10 alkyl (optionally substituted), aryl, C1-3 alkylaryl or C1-3 alkyloxyaryl; which comprises reacting a nitrile containing compound with an oxyamine of formula (II): R6ONH2 wherein R6 is as defined above for (I); in the presence of a thio-keto activating agent of formula (III): HS—Ry, —C(O)-Z wherein Z is -(1-4C)alkyl, —OH, —O-(1-4C)alkyl, —SH, —S(1-4C)alkyl, —NH2, —NH(1-4C)alkyl or —N[(1-4C)alkyl]2; Ry is (1-2C)alkyl (optionally substituted); or Z and Ry are linked so as to form a 5- or 6-membered ring of formula (IV): wherein X is —CH2—, —O—, —NH— or —N(1-4C)alkyl; p is 1 or 2; m is 1 or 2 and Rz is independently selected from H, (1-4C)alkyl, halo and amino.