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Suitable conditions have been determined for the catalytic dechlorination of chloropyrimidines. 5-Aminopyrimidine (I) has been synthesised from uracil, via 5-amino-2 : 4-dichloropyrimidine (I1 ; R = NH,), in 44% over-all yield. The chemical and some physical properties of the former have been examined and a number of derivatives prepared. 5-Aminopyrimidine did not give a diazonium salt, but its dichloro-derivative was converted by nitrous acid into diazouracil (VII) ; the mechanism of this reaction is discussed.

The stable hydantoin prostaglandin analogues (2b) and (3b) have been synthesised as racemic compounds. The less polar diastereoisomer of (2b) is a potent inhibitor of platelet aggregation in human platelet-rich plasma and its cyclohexyl analogue (22, R = CsHI1) has ca. 14 times the potency of prostaglandin E, in this test coupled with selectivity of biological action. Other structural modifications such as introduction of a 15-methyl group and insertion of the rn-phenylene or rn-oxaphenylene moieties into the acid side-chain of (2b) led to a reduction in anti-aggregatory potency. Synthesis of the imidazole (41 ) is described.