Chemoselective N‐Acylations of Amino Alcohols Mediated by Trimethylsilyl Cyanide

Abstract

We have recently reported on the resistance of silylated (thio)ethers and esters against acid chlorides and anhydrides allowing even Head-to-Tail peptide syntheses (1). Selective N-amide and urethane formation in general are very easily performed after the amino acid has been simply pretreaeted with trimethylsilyl cyanide ("US-CN) shortly before the acylation reaction, and no other precautions have to be taken for side-chain protection except for amino-type functionalities (2). We want to report shortly on our prelimenary findings that the scope of possible N-acylations performed selectively without accompanying 0-acylatione with polyfunctional amino alcohols can be generalized leading to improved reaction conditions and yields. -5 5 5 -

Conformational study by 1H NMR of the |D‐MePhe4|‐epimer of virginiamycin S1

“…Virginiamycin S (VS) constitutes the B factor of pairwise acting synergistic antibiotica of the synergimycin family produced by Stremtomyces Virgineae. Concomitantly with the A factor (VM), it irreversibly blocks the process of cell multiplication and protein synthesis (1,2 ) and the mode of action at the ribosomic level is currently the subject of intense studies The preparation of the MePhe' epimer ( 2 ) of the native VS1 (1) has recently been reported from these laboratories (4). VS-epi4 was obtained by re-cyclization of the opened linear peptide lactone called VS-seco (1) after strong activation of the latter (4,5), whereby partial epimerization was inevitable (6).…”

Note on “the Stereochemical Requirements for Long Range Coupling in α‐Halogenocyclohexanones”

“…In connection with the preceding paper by C. Jefford and B. Waegell[l], we want to stress some points which seem to us to be essential in the discussion of the pmr pecularities of 2-chloro-, and 2-bromo-3,3,5,5-tetramethylcyclohexanone (ll)*. Our attribution of the pmr signals in CDCI, to the appropriate hydrogen atoms was based [2] on the observation of two long range couplings, which are believed to follow a "classical" planar zig-zag path or M-mode: 1) the 45 coupling between one of the methyl signals with the B-parts of both H-4 and H-6 AB quartets and; 2) a ''large'' 45 coupling between the A parts of both H-4 and H-6 quartets (not shown in fig. l*).…”

Étude en RMN de La Bromo‐2 T‐Butyl Diméthyl‐4,4 Cyclohexanone trans Un Exemple De Couplage 4Jdiaxial

“…La valeur de la constante de couplage geminale indique que la repulsion electrostatique entre le groupement carbonyle et le brome[6] tend ii applatir lkgerement le plan C,-CO-C, et apporte une contribution [236, 291 plus importante a la constante de couplage geminale.Les protons H,, et H,, sont couples a longue distance (4J = 1.2 cps). Aucun des arguments critiques de Jefford et Waegell[2] ne peut s'appliquer ici.4OCONCLUSIONSLes rksultats obtenus au cours du present travail demontrent qu'un couplage a longue distance entre protons diaxiaux existe dans la bromo-2 1-butyl-5 dimethyl-4,4 cyclohexanone rrans (1) et confirment les conclusions d'Anteunis et Schamp[3]. Ces exemples, de m&me que ceux observes precedemment en serie heterocyclique[26] tendent a demontrer que I'attribution d'une configuration en se fondant uniquement sur la stereospecificitede couplages i i longue distance en W peut conduire i des rksultats erronb.…”