Dominique Florentin

Conformational analysis of linear peptides by 15N NMR spectroscopy using the enkephalin-related fragmetn Tyr—Gly—Gly—Phe as a model compound

The studies of the receptor-recognition processes of hormones or neuromodulators, such as enkephalins, and their structure-activity relationships require a preliminary knowledge of the conformational states of these peptidic molecules. ‘H NMR spectroscopy is the most commonly used method to study the structural behavior of peptides in solution [ 1,2]. For instance the formation of P-bends in oligopeptides can be evidenced by the smaller temperature dependencies of the amide protons involved in internal hydrogen bonds. Obviou~y the nitrogen atoms of these peptide bonds are affected by such bonding effects. Consequently the r5N NMR spectroscopy has been shown useful as an alternative method for the conformational studiesin cyclopeptides [3,7]. Here we extend this method to the conformational analysis of linear peptides using as a model Tyr-GlyGly-Phe [ I] which adopts a well-defined folded conformation both in DMSO solution and in the soiidstate [8,9]. This structure is characterized by a P-turn involving the CO and NH groups of the Tyr’ and Phe4 residues, reinforced by an electrostatic interaction. The r5N amide group chemical shift differences observed on changing the solvent (DMSO, HzO) and during the titration of the ionizable groups were compared for compound [I] and its N protected form t.boc-Tyr-Gly-Gly-Phe [II]. The structure already proposed for [I] in DMSO is confirmed and the results are extended: In water peptides [I] and [II] are unfolded irrespective of their ionization state;

Acetals Oxidation Into Esters with Electrophilic Halogens

Abstract A preparative oxidation of dioxolanes groups into esters is described. Among the different electrophilic halogens and solvents which have been tested, ICl/H2O in methylene chloride and Br2/H2O in acetonitrile gave the best results.

Synthesis and biochemical properties of Z- and E-4,5-dehydrodethiobiotin

Radical species are postulated intermediates in the formation of the carbon-sulfur bonds of biotin. It was of interest to examine the behaviour of unsaturated analogues which should give rise to allylic radicals. The two isomers of 4,5-dehydrodethiobiotin have been synthesized and labelled with 14C on their carboxylic acid group. When incubated with an in vitro system capable of transforming dethiobiotin into biotin, they covalently label biotin synthase.

Formation of boroncarbon bonds through silyl derivatives

Abstract The synthesis of new B -substituted boron heterocycles can be achieved in high yields by using silyl ether derivatives of hydroxyboron compounds as intermediates. This method has numerous advantages over previous techniques; in particular it permits the use of organolithium reagents.

SYNTHESIS OF PROTEIN CONJUGATES OF 2-CARBOXY-L-ARABINITOL 5-PHOSPHATE AND 2-CARBOXY-L-RIBITOL 5-PHOSPHATE

Abstract The synthesis of 5-O-[5-(pentanoic acid)]-phosphono-L-erythro-pent-2-ulose 2 was successfully achieved by coupling benzyl 5-hydroxypentanoate 9b and 1-O-benzyl-L-erythro-pent-2-ulose ethane- 1,2-diyl dithioacetal 13 with the enediol pyrophosphate 18. Compound 2 was coupled to carrier proteins, porcine thyroglobuline and bovine serum albumin and the conjugates were treated with KCN to give conjugates of the hapten 1, designed to raise catalytic antibodies.