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.

Platelet glycoprotein (GP) IIb-IIIa inhibitors may become useful antithrombotic agents. Ro 4–5054 is a low molecular weight, noncyclic, peptidomimetic inhibitor that is three orders of magnitude more potent than RGDS in inhibiting fibrinogen binding to purified GPIIb-IIIa and in preventing platelet aggregation. Comparisons of RGDS and Ro 4–5054 in cell adhesion assays showed that, in contrast to RGDS, Ro 4–5054 was highly selective GPIIb-IIIa inhibitor. Effects of RGDV and Ro 4– 5054 on the conformation and activation state of GPIIb-IIIa were also examined. RGDV and Ro 4–5054 induced conformational changes in purified inactive GPIIb-IIIa as determined by binding of the monoclonal antibody D3GP3 (D3). These conformational alterations were not reversed after inhibitor removal, as indicated by the continued exposure of the D3 epitope and a newly acquired ability to bind fibrinogen. Similarly, RGDV and Ro 4–5054 induced conformational changes in GPIIb-IIIa on the intact platelet. However, after removal of the inhibitors, exposure of the D3 epitope was fully reversed and the platelets did not aggregate in the absence of agonist. Thus, while RGD(X) peptides and Ro 4–5054 transformed purified inactive GPIIb-IIIa into an irreversibly activated conformer, the effects of these inhibitors were reversible on the intact platelet. This suggests that factors present in the platelet membrane or cytoplasm may regulate in part the ability of the complex to shift between active and inactive conformers.

Werrn Professor K. Mahlcr zum 90. Geburtstdg gewidmet (2O.VIII. 75) A novel route to imldaz,oles and their use for the syntheeis of purines and 4,6-dG hydro-l,?-dlmethyl-8-pheny~dazo[4,5-e]-l,4-d~zepln-~l~-on. Summary. Recently it has been shown [Z] that pyrimidines are avaihble from Thor+e-Ziegler cyclization of the appropriate dinitriles. As an extension of this work, a novel route to imidazoles has been developed.It has bean demonstrated that thcse imidawle derivatives are valuable intermediates for the synthesis of purines by application of standard procedures. Tho use of these imidazoles has enabled the preparation of some derivatives not accessible by other methods. Durch Thorpe-Z~~~~"Cyclisierung von Dinitden sind viele 5-,6und 7-gliedrige P-Cyan-efiamine und deren Folgeprodukte zughglich [l], In der vorausgegangenen Mitteilung [2] wurde gezeigt, dass der Aufbau des Pyrirnidinringes ausgehend von W-Cyano-N-(2-cyanoathy1)-acetarnidin rniiglich ist. In Fortfiihrung dieser Untersuchungen konnte erwartet werden, dass sich die bisher unbekannten N'-Cyano-Ncyanomethylderivate des Acetamidins zur Herstellung vdn Imidazolen eignen wiirden. Ein Hinweis dafiir bildete die leichte Cyclisierung von N-Cyanimino-dithiokohlensaureestern zu Imidazolen, uber die von Gomp$er et ad. [3] berichtet wurde.

Platelet glycoprotein (GP) IIb-IIIa inhibitors may become useful antithrombotic agents. Ro 4–5054 is a low molecular weight, noncyclic, peptidomimetic inhibitor that is three orders of magnitude more potent than RGDS in inhibiting fibrinogen binding to purified GPIIb-IIIa and in preventing platelet aggregation. Comparisons of RGDS and Ro 4–5054 in cell adhesion assays showed that, in contrast to RGDS, Ro 4–5054 was highly selective GPIIb-IIIa inhibitor. Effects of RGDV and Ro 4– 5054 on the conformation and activation state of GPIIb-IIIa were also examined. RGDV and Ro 4–5054 induced conformational changes in purified inactive GPIIb-IIIa as determined by binding of the monoclonal antibody D3GP3 (D3). These conformational alterations were not reversed after inhibitor removal, as indicated by the continued exposure of the D3 epitope and a newly acquired ability to bind fibrinogen. Similarly, RGDV and Ro 4–5054 induced conformational changes in GPIIb-IIIa on the intact platelet. However, after removal of the inhibitors, exposure of the D3 epitope was fully reversed and the platelets did not aggregate in the absence of agonist. Thus, while RGD(X) peptides and Ro 4–5054 transformed purified inactive GPIIb-IIIa into an irreversibly activated conformer, the effects of these inhibitors were reversible on the intact platelet. This suggests that factors present in the platelet membrane or cytoplasm may regulate in part the ability of the complex to shift between active and inactive conformers.

Breder ec k, Edenkofer : [ Jahrg. 88 60 ccm Wasser und 100 ccm Athano1 hinzugefugt und 2 Stdn. unter RiickfluB zum Sieden erhitzt. Anschliehnd dampfte man den Alkohol ab, versetzte mit 60 ccm 20-proz. w&Br. Natronlauge, kochte nochmals 2l/, Stdn. und filtrierte nach dem Abkiihlen von Spuren amorpher Substanz ab. Unter Riihren und Kiihlen wurde die alkahche Lijsung d m h troptenWeise Zugabe von etwa 45 ccm konz. Salzsiiure auf 1 gebmcht (Vorsicht, BlausiLure-Entwicklung!), noch Stde. auf 0 0 gekiihlt, dann das ausgefallene Heteroa u x i n abgesaugt und mit wenig eiskaltem Waaser gewaschen. Ausb. 3.39g (97% d.Th.) vom Schmp. 155-160O (Sintern ab 145O). Bus Waaaer erhiilt man XXVI in 75-80-proz. Ausbeute mit dem Schmp. 164-165O; keine Schmp.-Erniedrigung mit authent.80) XXVI vom gleichen Schmp. Aus Gmmin erhielten wir unter den gleichen Bedingungen nur etwa 30% reines Heteroauxin.