The present invention relates to novel compounds which are protein kinase C inhibitors, methods for their preparation, intermediates therefor and pharmaceutical compositions comprising them. More particularly, the present invention relates to compounds of formula (I): wherein: one of Ar1 and Ar2 is optionally substituted bicyclic heteroaryl or optionally substituted tricyclic heteroaryl and the other is optionally substituted heteroaryl or optionally substituted aryl; X is O or S; and R is H, OH, NH2 or C1-6 alkyl (itself optionally substituted by amino or hydroxy); or a salt or solvate thereof, or a solvate of a salt thereof; and the use of such compounds in medical therapies.