Novel compounds and pharmaceutical compositions useful as hypocholesterolemic and hypolipidemic agents are described. More specifically, potent inhibitors of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase ("HMG CoA reductase") are described. Methods of using such compounds and compositions to treat subjects, including humans, suffering from hyperlipidemia, hypercholesterolemia, hypertriglyceridemia, atherosclerosis, Alzheimer's Disease, benign prostatic hypertrophy (BPH), diabetes and osteoporosis are also described.