Compounds of the formula (I): and N-oxides, salts and stereoisomers thereof wherein A is OR.sup.1, NHS(.dbd.O).sub.pR.sup.2, NHR.sup.3, NRaRb, C(.dbd.O)NHR.sup.3 or C(.dbd.O)NRaRb wherein; R.sup.1 is hydrogen, C.sub.1-C.sub.6alkyl, C.sub.0-C.sub.3alkylenecarbocyclyl, C.sub.0-C.sub.3alkyleneheterocyclyl; R.sup.2 is C.sub.1-C.sub.6alkyl, C.sub.0-C.sub.3alkylenecarbocyclyl, C.sub.0-C.sub.3alkyleneheterocyclyl or NRaRb; R.sup.3 is C.sub.1-C.sub.6alkyl, C.sub.0-C.sub.3alkylenecarbocyclyl, C.sub.0-C.sub.3alkyleneheterocyclyl, --OC.sub.1-C.sub.6alkyl, --OC.sub.0-C.sub.3alkylenecarbocyclyl, --OC.sub.0-C.sub.3alkyleneheterocyclyl; wherein any alkyl, carbocyclyl or heterocycylyl in R.sup.1, R.sup.2 or R.sup.3 are optionally substituted p is independently 1 or 2; n is 3, 4, 5 or 6; denotes an optional double bond; Rq is H or when L is CRz, Rq can also be C.sub.1-C.sub.6alkyl; Ry and Ry' are independently C.sub.1-C.sub.6alkyl; L is N or CRz; Rz is H or forms a double bond with the asterisked carbon; W is --CH.sub.2--, --O--, --OC(.dbd.O)NH--, --OC(.dbd.O)--, --S--, --NH--, --NRa, --NHS(.dbd.O).sub.2--, --NHC(=0)NH-- or --NHC(.dbd.O)--, --NHC(.dbd.S)NH-- or a bond; R.sup.8 is an optionally substituted ring system containing 1 or 2 saturated, partially saturated or unsaturated carbo or heterocyclic rings have utility in the inhibition of NS-3 serine proteases, such as flavivirus infections. ##STR00001##