Low haematocrit values are generally well tolerated in terms of oxygen transport but a low haematocrit might interfere with blood coagulation. We thus sampled 60 ml of blood in 30 healthy volunteers. The blood was centrifuged for 30 min at 2000 g and separated into plasma, which contained the platelet fraction, and packed red blood cells. The blood was subsequently reconstituted by combining the entire plasma fraction with a mixture of packed red blood cells, 0.9% saline, so that the final haematocrit was either 40, 30, 20, or 10%. Blood coagulation was assessed by computerized Thrombelastograph analysis. Data were compared using repeated measures analysis of variance and post-hoc paired t-tests with Bonferroni correction. Decreasing the haematocrit from 40 to 10% resulted in a shortening of reaction time (r) and coagulation time (k), and an increase in angle alpha, maximum amplitude (MA) and clot strength (G) (all P<0.02). This pattern represents acceleration of blood coagulation with low haematocrit values. The isolated reduction in haematocrit, therefore, does not compromise in vitro blood coagulation.

The 2‐(p‐diphenyl)‐isopropyloxycarbonyl (Dpoc) residue has been chosen for the selective protection of α‐amino groups in the synthesis of peptides containing additional acid‐labile protecting residues. It is easily introduced into amino‐acids by reacting either the mixed carbonate I or the azide III with esters or salts of amino‐acids. It is split by dilute acetic acid and other weakly acidic reagents at rates which permit a selective cleavage in the presence of other acid‐labile protecting groups, especially those derived from t‐butanol A number of peptide syntheses have been carried out with the new group either in the conventional manner or by the solid‐phase method. No effects due to steric hindrance, as observed previously with the N‐trityl residue, are encountered. The application of the Nα‐Dpoc group to solid‐phase peptide synthesis permits the use of a new combination of protecting groups in which the side chains of trifunctional amino‐acids are blocked by acid‐labile residues that can be easily split in the final step of the synthesis.

The selective cleavage of the N‐sulphenyl protecting group from amino‐acids and peptides containing additional acid‐labile protecting residues has been investigated. Among various nucleophilic reagents tested for their ability to effect rapid and specific removal of the N‐sulphenyl groups, hydrogen cyanide, sulfurous acid and thioacetamide have been found to be particularly suitable. The application of this method to the solid phase synthesis of peptides is described and discussed.

6 ) Dieser Versuch wurde ausgefuhrt, bevor feststand, dass das Produkt S-frei wax. 6 ) J . Mimaas, R. 51, 475 (1932). R. C. Elderfield, J. Org. Chem. 7, 247 (1942). B1. [5], 7, 781 (1940). Volumen XXIX, Fasciculus III (1946). __-1) Dieser Versuch wurde ausgefuhrt, um die TsO-Gruppe durch CH3S-zu er-2) J . Minsaas, R. 51, 475 (1932). 3, Keller, H., und v. Halban, H., Helv. 28, 542 (1945) und die dort angefiihrten setzen. Die Acetonabspaltung trat wahrscheinlich bei der Druckhydrierung ein. friiheren Veroffentlichungen. 4, Paal, C., und Schulze, H., B. 35, 174 (1902).

Carbonsaureester, welche in der Alkoholkomponente an geeigneter Stelle negative Substituenten tragen, besitzen Eigenschaften von Acylierungsmitteln. Solche sogenannte ,,aktivierte Ester" eignen sich besonders zur Synthese von Peptiden.Wahrenddem der Einfluss des negativen Substituenten auf die Carboxylgruppe in den a l i p h a t i s c h e n a,ktivierten Estern wesentlich induktiver Natur sein durfte2), ist in den in 0 -oder p-Stellung negativ substituierten a r o m a t i s c h e n aktivierten Estern wahrscheinlich ein elektromerer Mechanismus wirksam (Schema 1, a und b) :Infolgedessen ist bei negativ substituierten aromatischen Estern eine besonders starke Aktivierung zu erwarten.Diese Erwartung wurde durch Untersuchungen von Boddnnsxky und Mitarbeitern3) bestatigt. Trotzdem haben sktivierte Arylester bisher wenig praktische Verwendung gefunden. Das liegt zur Hauptsache an ihrer relativ schweren Zuganglichkeit. I m Gegensatz zu aktivierten Alkylestern, welche direkt aus Carbonsawen und substituierten Halogenalkylen gewonnen werden konnen (Schema 2, a), mussten aktivierte Arylester auf dem Umwege iiber Saureanhydride oder -halogenide hergestellt werden (z. B. Schema 2, b):