Compounds are provided of the following structure are HMG CoA reductase inhibitors and thus are active in inhibiting cholesterol biosynthesis, modulating blood serum lipids, for example, lowering LDL cholesterol and/or increasing HDL cholesterol, and treating hyperlipidemia and dyslipidemia, hypercholesterolemia, hypertriglyceridemia and atherosclerosis ##STR00001## wherein variables A and B are defined herein.