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The microsomal triglyceride (TG) transfer protein (MTP) is a heterodimeric lipid transfer protein that catalyzes the transport of triglyceride, cholesteryl ester, and phosphatidylcholine between membranes. Previous studies showing that the proximal cause of abetalipoproteinemia is an absence of MTP indicate that MTP function is required for the assembly of the apolipoprotein B (apoB) containing plasma lipoproteins, i.e., very low density lipoproteins and chylomicrons. However, the precise role of MTP in lipoprotein assembly is not known. In this study, the role of MTP in lipoprotein assembly is investigated using an inhibitor of MTP-mediated lipid transport, 2-[1-(3, 3-diphenylpropyl)-4-piperidinyl]-2,3-dihydro-1H-isoindol-1-one (BMS-200150). The similarity of the I[C.sub.50] for inhibition of bovine MTP-mediated TG transfer (0.6 [[micro]molar]) to the [K.sub.d] for binding of BMS-200150 to bovine MTP (1.3 [[micro]molar]) strongly supports that the inhibition of TG transfer is the result of a direct effect of the compound on MTP. BMS-200150 also inhibits the transfer of phosphatidylcholine, however to a lesser extent (30% at a concentration that almost completely inhibits TG and cholesteryl ester transfer). When BMS-200150 is added to cultured HepG2 cells, a human liver-derived cell line that secretes apoB containing lipoproteins, it inhibits apoB secretion in a concentration dependent manner. These results support the hypothesis that transport of lipid, and in particular, the transport of neutral lipid by MTP, plays a critical role in the assembly of apoB containing lipoproteins.

An enantioselective synthesis of the squalene synthase inhibitor, alpha-phosphono sulfonate triacid 1, was conducted. Deuterium incorporation investigations were performed first to determine the configurational stability of the chiral centers. Results indicated that both the triacid 1 and diester 2 were isolable as single enantiomers, whereas triester 3 was very sensitive to racemization. The method for the introduction of the asymmetric center was based on the sulfuration or alkylation of a chiral phosphorus carbanion.