HETEROARYL-CYCLIC ACETALS

Compounds of formula (I) are described in which Het is a five or six membere d heteroaromatic ring of formula (i) in which one of R1 and R2 is optionally substituted heteroaryl and the other is optionally substituted heteroaryl or optionally substituted aryl; X1 is a bond, X3 and X4 are each independently N or C and X2 and X5 are independently CH, N, NH, O or S; or X3 and X4 are C, one of X1, X2 and X5 is N and the others are N or CH; but excluding compounds in which X1 is a bond, one of X2 and X5 is N and the other is NH and X3 and X4 are both C; R3 represents a group -L1-R6; R4 represents hydrogen, alkyl or hydroxyalkyl; or R3 and R4, when attached to the same carbon atom, may form with the said carbon atom a cycloalkyl, cycloalkenyl or heterocycloalkyl ring or a group C=CH2; R5 represents hydrogen or alkyl; and m is zero or an integer 1 or 2; and N-oxides thereof, and thei r prodrugs; and pharmaceutically acceptable salts and solvates of compounds of formula (I) and N-oxides thereof, and their prodrugs. The compounds are TNF inhibitors and are useful as pharmaceuticals.