Tetrahydrolipstatin inhibits pancreatic lipase from several species, including man, with comparable potency. The lipase is progressively inactivated through the formation of a long-lived covalent intermediate, probably with a 1:1 stoichiometry. The lipase substrate triolein and also a boronic acid derivative, which is presumed to be a transition-state-form inhibitor, retard the rate of inactivation. Therefore, in all probability, tetrahydrolipstatin reacts with pancreatic lipase at, or near, the substrate binding or active site. Tetrahydrolipstatin is a selective inhibitor of lipase; other hydrolases tested were at least a thousand times less potently inhibited.

Lipstatin, a new and very potent inhibitor of pancreatic lipase (the key enzyme of intestinal fat digestion) was isolated from Streptomyces toxytricini. Lipstatin contains a £-lactone structure that probably accounts for the irreversible lipase inhibition. The IC50 of lipstatin for pancreatic lipase is 0.14 fiu. In mice triolein absorption was dose-dependently inhibited by lipstatin, whereas oleic acid was absorbed normally. Other pancreatic enzymes, such as phospholipase A2 and trypsin, were not inhibited even at an inhibitor concentration of200jum.

The tetrapeptide H-Arg-Gly-Asp-Ser-OH (1) (RGDS), representing a recognition sequence of fibrinogen for its platelet receptor GP IIb-IIIa (integrin alpha IIb beta 3), served as lead compound for the development of highly potent and selective fibrinogen receptor antagonists. Replacement of the N-terminal arginine by p-amidinophenylalanine or the Gly moiety by m-aminobenzoic acid led to compounds which are superior to the lead peptide with regard to activity and selectivity for GP IIb-IIIa vs the closely related vitronectin receptor alpha v beta 3. By random screening [(p-amidinobenzenesulfonamido)ethyl]-p-phenoxyacetic acid derivatives have been identified as fibrinogen receptor antagonists. Further structure-activity relationship studies culminated in the preparation of N-[N-[N-(p-amidinobenzoyl)-beta-alanyl]-L-alpha-aspartyl]-3-phenyl-L- alanine (29h, Ro 43-5054) and [[1-[N-(p-amidinobenzoyl)-L-tyrosyl]-4-piperidinyl]oxy]acetic acid (37f, Ro 44-9883), which exhibit very high activity as platelet aggregation inhibitors (IC50s 0.06 and 0.03 microM, respectively, human PRP/ADP) as well as marked selectivity for GP IIb-IIIa vs alpha v beta 3. Since the activity of 37f in dogs declines according to a two-compartment model with an initial phase having a t1/2 of 8 min and a second phase with a t1/2 of 110 min, this compound is a suitable candidate for the development as iv platelet inhibitor.

The inhibition of digestive lipases by the antiobesity drug Orlistat along with lipolysis levels and fecal fat excretion were measured in healthy humans. Orlistat was found to be a powerful gastric lipase inhibitor, achieving 46.6--91.4% enzyme inhibition and thus greatly reducing gastric lipolysis of solid and liquid meals (11--33% of respective controls). Gastric lipase inhibition by Orlistat was extremely fast (half-inhibition time < 1 min). Duodenal lipolysis was reduced significantly by Orlistat given with the solid meal (32.6--37.6% of controls) but was only slightly reduced by Orlistat given with the liquid meal (74.5--100% of controls). Human pancreatic lipase (HPL) inhibition was found to be high (51.2--82.6%), however, regardless of the meal. These paradoxical results were explained when in vitro lipolysis experiments were performed. The rates of HPL inhibition by Orlistat were found to be similar with both types of meals (half-inhibition time 5--6 min), but the preemulsified triglycerides of the liquid meal were rapidly hydrolyzed by HPL before the enzyme was significantly inhibited by Orlistat. With the solid meal, the rate of hydrolysis of the meal triglycerides by HPL was slower than the rate of HPL inhibition by Orlistat. As predicted from the previous results, the effects of Orlistat on fat excretion levels were found to be much greater with the solid (40.5--57.4% of ingested fat) than with the liquid (4.2--18.8%) test meal.