Compounds are provided having the following structure which 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, dyslipidemia, hormone replacement therapy, hypercholsterolemia, hypertriglyceridemia and atherosclerosis as well as Alzheimer's disease and osteoporosis ##STR00001## wherein X is N or CR.sub.5; and pharmaceutically acceptable salts thereof, ##STR00002## wherein R.sub.1 to R.sub.7 are as defined herein.A method for treating the above diseases employing the above compounds is also provided.