No abstract

Lipoprotein lipase (LPL) plays a central role in triglyceride (TG) metabolism. By catalyzing the hydrolysis of TGs present in TG-rich lipoproteins (TRLs), LPL facilitates TG utilization and regulates circulating TG and TRL concentrations. Until very recently, structural information for LPL was limited to homology models, presumably due to the propensity of LPL to unfold and aggregate. By coexpressing LPL with a soluble variant of its accessory protein glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1) and with its chaperone protein lipase maturation factor 1 (LMF1), we obtained a stable and homogenous LPL/GPIHBP1 complex that was suitable for structure determination. We report here X-ray crystal structures of human LPL in complex with human GPIHBP1 at 2.5-3.0 Å resolution, including a structure with a novel inhibitor bound to LPL. Binding of the inhibitor resulted in ordering of the LPL lid and lipid-binding regions and thus enabled determination of the first crystal structure of LPL that includes these important regions of the protein. It was assumed for many years that LPL was only active as a homodimer. The structures and additional biochemical data reported here are consistent with a new report that LPL, in complex with GPIHBP1, can be active as a monomeric 1:1 complex. The crystal structures illuminate the structural basis for LPL-mediated TRL lipolysis as well as LPL stabilization and transport by GPIHBP1.

Steroid sulfatase (STS) has emerged as a highly attractive target for the therapy of a number of disorders. Starting with the known inhibitor estrone sulfamate (1) as lead compound and with the finding that steroid sulfamates containing a nonaromatic A-ring are inactive, chromen-4-one sulfamates were designed, prepared, and tested for their ability to block human STS. This new class of nonsteroidal inhibitors shows high potency when the sulfamate group and the side chain are situated in diagonally opposite positions (i.e., 2,6- and 3,7-substitution pattern). The highest activity is achieved with fully branched, bulky aliphatic side chains and with thiochromen-4-one as the core element. 2-(1-Adamantyl)-4H-thiochromen-4-on-6-O-sulfamate (6c) is the most potent STS inhibitor discovered so far, and it is about 170-fold superior to 1. As with 1, all chromenone sulfamates are irreversible inhibitors of STS with a biphasic time course of inactivation.

A convenient procedure for the synthesis of 2-heterosubstituted statine derivatives as novel building blocks in HIV-protease inhibitors has been developed. The synthesis starts with protected L-phenylalaninols, which were converted to gamma-amino alpha, beta-unsaturated esters in a one-pot procedure. A highly diastereoselective epoxidation of the N-protected (E)-enoates, followed by regioselective ring opening of the corresponding 2,3-epoxy esters with a variety of heteronucleophiles, resulted in 2-heterosubstituted statine derivatives. The overall stereo-chemical outcome of the transformations meets the required configuration of HIV-protease inhibitors. The short, synthetically flexible, and highly diastereoselective synthesis of 2-heterosubstituted statines has enabled a broad derivation, covering the S3, S2, and S1'-S3' sites of the enzyme. In a series of 46 derivatives, several potent inhibitors were obtained with Ki values as low as 3.4 nM and antiviral activity in the lower nanomolar-range. The structural parameters of the compounds which determine the potency of inhibition and selectivity for the viral enzyme are discussed.

Asymmetrische Synthesen uber heterocyclische Zwischenstufen, XXIVI). -Enantioselektive Synthese von (R)-a-Methyltryptophan-methylester und D-Tryptophan-methylester nach der Bislactimether-MethodeDie Titelverbindungen wurden durch asymmetrische Synthese nach der Bislactimether-Methode hergestellt (e.e. iiber 95% bzw. etwa 90%).Recently, Brana et al.2) reported on the asymmetric synthesis of a-methyltryptophane (by methylation of the lithium derivative of N-benzylidenetryptophane methyl ester). However, in our hands this method gives -as expected -essentially racemic material3). This communication describes the asymmetric synthesis of methyl (R)-a-methyltryptophanate (8a; e. e. > 95 Yo) and of methyl D-tryptophanate (8b; e.e. ca. 88%) starting with the lithiated bislactim ethers 2 a and 2 b of cycle(-L-Val-Ala-) and cyclo(-~-Val-Gly-)4). Upon alkylation of 2a or 2 b with N-Boc-3-(bromomethy1)indole (3) the alkylation products 4 a and 4 b with (3R) configuration are formed with d.e. more than 95% and ca. 88070; respectively 1d.e. = 070 (3R) -To (3S)I.The configuration of the main (3R) isomer of the compounds 4 can be assigned by 'H NMR spectroscopy using -as in analogous cases5) -the fact that the (3R) isomer has a "folded" conformation (type 5) with the 6-H located within the shielding cone of the heteroaromatic indole ring; consequently its 'H NMR signal suffers an upfield shift.On acid hydrolysis (4a: 0.1 N HCI, 2 equivalents, room temperature, 14 days; 4b: 0.1 N HCI, 2 equivalents, room temperature, 5 days) 4a and b are cleaved to give methyl L-valinate (6), N-Boc-protected methyl (R)-a-methyltryptophanate (7a; e. e. > 95 %), and methyl o-tryptophanate (7b; e.e. ca. 90%). In both cases L-valinate 6 could be separated by fractional bulb-tobulb destillation. With 4 N HCI at room temperature the Boc protecting group is removed to give methyl (R)-a-methyltryptophanate (8a) ( Methyl (R)-a-methyltryptophanate (8a) was alternatively obtained from the lithiated bislactim ether 9 of cyclo(-~-Ala-~-Ala-)~) by the analogous route tlia 10. The bislactim ether 10 is more readily hydrolyzed than 4a, but the degree of asymmetric induction is somewhat lower (d.e. ca. 90%).