Summary. Phthalimides, 4-nitrophthalimides, and tetrachlorophthalimides (exemplified by methyl Na-phthalyl-glycinate, 4-nitroplithalimide, ethyl Na-(4-nitrophthalyl)-glycinate, and methyl Na-tetrachlorophthalyl-glycinate) give colored molecular cornplexes with Na-benzyloxycarbonyl-ar-pentamethyl-phenylalanine, P\T"-acetyl-p-dimethylarnino-phenylalanine, and Naacetyl-tryptophane, as well as with the simpler compounds hexamethylbenzene, N, N-dimethylaniline, N, N-dimethyl-p-toluidine, and indole, in various organic solvcnts.The association constants arc small, and vary between 0.4 and 1.2 l/mol as measured spectroscopically. Enthalpies of complex formation lie between (-) 0.5 and (-) 2.5 kcal/mole. They are within the range assuincd for VAN DBR WAALS interactions between hydrophobic side-chains of amino-acids. This is essential if one mould want t o use such complexes as intra-or intermolecular conformational probes in synthetic polypeptides.The broad absorption maxima of the complexes lie between 350 and 490 nm, extinction coefficients are in the range reported for charge transfer complexes, 500 to 2000. '4ssignment of the long wavelength absorption to a charge transfer transition seems quite justified by the calculated values of energy coefficients (HMO-method) for the new class of phthalimide ucceptors and the donors, as well as by the applicability of the BRIEGLEB relationship between h v,,,, ionisation energy, electron affinity, and distance between the planes of donor and acceptor in the complex between ethyl Na-(4-nitrophthalyl)-glycinatc and hexamethylbenzene. On the basis of absorption maxima, the relativc acceptor strengths are : 4-nitrophthalimide > tetrachlorophthalimide > phthalimide.Phthalyl, nitrophthalyl, and tetrachlorophthalyl derivatives of tryptophane, pentaniethylphcnylalanine, and p-dirnethylainino-phenylalanine are colored compounds and behave like intrunzoleculur charge transfer complexes.The syntheses of all required compounds are described. N-Ethoxycarbonyl derivatives of 4-nitrophthalimide and of tctrachlorophthalimidc are used to prepare 4-nitrophthalyl and tetrachlorophthalyl derivatives of amino-acids.

Volumen 47, Fasciculus 2 (1964) -No. 54 44 1 54. Verdoppelungserscheinungen beim Ringschluss von Peptiden V. Relative Bedeutung der sterischen Hinderung und der Assoziation iiber Wasserstoff-Briicken bei Tripeptiden. Spektroskopische Versuche zur Konformationsbestimmungl). 12. Mitteilung iiber homodet cyclische Polypeptide [l] 2, von R. Schwyzer3), J. P. Carribn, B. Gorup, H. Nolting und Aung Tun-Kyi (21. XII. 63) 1. Problemstellung

The syntheses and properties of p‐nitrobenzyl diazoacetyl‐glycinate (VI), p‐nitrobenzyl p‐(p‐methoxyphenylazo)‐benzyloxycarbonyl‐glycyl‐glycollyl‐glycinate (II) and p‐nitrobenzyl p‐phenylazo‐benzyloxycarbonyl‐glycyl‐glycollyl‐glycinate are described. These compounds have been prepared as intermediates for the synthesis of other depsipeptides.