Synthesis of non-proteinogenic amino acids from N-(4-toluenesulfonyl)dehydroamino acid derivatives

By treating N-(4-toluenesulfonyl)-N-(tert-butyloxycarbonyl)-dehydroamino acid derivatives with different reactants under different conditions, a variety of new amino acids are obtained, viz. (i) alpha-alcoxy-alpha-amino acids, (ii) alpha,alpha-diamino acids and (iii) novel beta-substituted dehydroamino acids. (C) 2002 Elsevier Science Ltd. All rights reserved.Fundação para a Ciência e a Tecnologia for financial support (project no. POCTI/ 1999/QUI/32689)

Electrochemical synthesis of diaminodicarboxylic acid derivatives

Diaminoadipic acid derivatives were synthesized in good yields by electrolysis of N,N-diacyidehydroalanines. Cyclic voltammetry measurements on the precursors are presented and interpreted as supporting formation of a nucleophilic intermediate generated by electrochemical reduction. (C) 2003 Elsevier Science Ltd. All rights reserved.- Fundação para a Ciência e a Tecnologia (project no. POCTI/1999/QUI/32689)

Synthesis of 2,3,5-substituted pyrrole derivatives

2,3,5-Substituted pyrrole derivatives are prepared by treatment of 2,3-dihydrofuran derivatives with trifluoroacetic acid. These in turn are obtained by Michael addition of carbon nucleophiles of the beta-dicarbonyl type to N-(4-toluenesulfonyl)-N-(tert-butyloxycarbonyl)-dehydroalanine methyl ester.- Fundação para a Ciência e a Tecnologia(POCTI/1999/QUI/32689

Cyclic voltammetry studies on substituted arenesulfonhydrazides

Additional Z and Boc groups on the vicinal nitrogen of sulfonyl hydrazines have no significant effect on the cathodic potential of the sulfonyl functions as measured by cyclic voltammetry, whereas a Boc group on the geminal nitrogen invariably gives rise to shifts of about 0.2 V to less negative potential similar to those previously observed for derivatives of amines.This work was supported by the Swedish Natural Science Research Council (NFR) and the Fundaçao para a Ciência e a Tecnologia (Portugal)

Efficient synthesis of dehydroamino acid derivatives

By using a DMAP catalysed reaction of P-hydroxyamino acid derivatives with tert-butylpyrocarbonate, the corresponding dehydroamino acid derivatives were obtained in high yields.- (undefined

Selective cathodic cleavage of unsymmetrical imidodicarbonates, acylcarbamates and diacylamides

A study of the selective cathodic cleavage of one of the alkoxycarbonyl or acyl groups from various imidodicarbonates, acylamides, and diacylamides is reported. The compounds investigated include all 15 possible combinations of the following groups in unsymmetrical N,N-diprotected derivatives of benzylamine: p-nitrobenzyloxycarbonyl, trichloroethyloxycarbonyl, toluene-p-sulfonyl, benzoyl, benzyloxycarbonyl, and tert-butyloxycarbonyl which can all be electrochemically cleavaged, except the last one. Initially the compounds were examined by cyclic voltammetry in order to measure the potentials associated with the cleavage of each group and afterwards they were electrolysed at constant potential in the presence of a proton donor. The following ranges in negative potential were recorded: 1.03-1.13 V [Z(NO2)], 1.8-2.14 V (Troc), 1.75-2.41 V (Tos), 1.88-2.52 V (Bz), and 2.83-2.9 V (Z), thus occasionally revealing a drastic effect of the auxiliary group. In the electrolytic experiments competitive attack by base occasionally led to mixtures of monoacylamides. However, all compounds apart from some of the trichloroethyloxycarbonyl derivatives could be selectively cleaved in 89-100% yields when an appropriate proton donor was used. Tentative explanations are given for the behaviour of the compounds studied and some conclusions are drawn

2-naphthalenesulfonyl as a tosyl substitute for protection of amino functions. Cyclic voltammetry studies on model sulfonamides and their preparative cleavage by reduction

With the aim to develop a practically useful, reductively more labile alternative to tosyl for protection of amino functions, initially a number of N-arenesulfonyl-protected heterocycles (pyrroles, imidazoles, indole, and carbazole) have been prepared and studied by cyclic voltammetry (CV). The recorded activation potentials vary from -1.32 to -1.99 V (vs SCE). In N-sulfonylazolides such as tosylindole the cathodic potentials are shifted by over 0.5 V compared to simple sulfonamides. An additional effect of the sulfonic acid component is also indicated. Among the compounds studied, 1- and 2-naphthalenesulfollylindole give CV peaks at about 0.4 and 0.2 V, respectively, less negative potential than tosylindole. To further investigate naphthalenesulfonyl for this purpose, we have also prepared a variety of simple 1- and 2-naphthalenesulfonyl derivatives and studied them similarly. They have activation potentials above -2.14 V and are all smoothly cleaved by Mg/MeOH. The latter reagent is capable of cleaving N-arenesulfonyl derivatives that give CV peaks above -2.30 V, whereas Al(Hg) requires potentials above about -1.7 V. Selective cleavage of 2-naphthalenesulfonyl in the presence of tosyl by Mg/MeOH is demonstrated. Several examples of reductive cleavage of arenesulfonyl derivatives with Mg/MeOH, Al(Hg), and electrolysis on a preparative scale are given.This work was supported by the Swedish Natural Science Research Council (NFR), the Swedish Research Council for Engineering Sciences (TFR), Carl Tryggers Stiftelse, Astra Draco AB, and the Fundacão para a Ciência e a Tecnologia (Portugal). B.N. gratefully acknowledges the RSC for a journals grant for international authors and the ISP for a fellowship, as well as the University of Yaoundé I for a leave of absence

Novel aziridine esters by the addition of aromatic nitrogen heterocycles to a 2H-azirine-3-carboxylic ester

Methyl 2-(2,6-dichlorophenyl)-2H-azirine-3-carboxoylate acts as an efficient alkylating agent for a variety of five-membered aromatic heterocycles. The aziridines derived from heterocycles that bear an alpha-carbonyl substituent react with TFA to give pyrroloimidazoles; 2,6-dichlorobenzaldehyde is also produced.- (undefined

Synthesis and cathodic cleavage of a set of substituted benzenesulfonamides including the corresponding tert-butyl sulfonylcarbamates: pKa of sulfonamides

From a series of Substituted benzenesulfonic acids, most of which have previously been employed for the protection of amino functions and including a few such known to facilitate cleavage by acid, benzylamides 1a-k have been derived and studied. Initially their electrochemical cleavage potentials were determined by cyclic voltammetry in order to further explore selective deprotection within this substance group. In parallel, the corresponding tert-butyl sulfonylcarbamates 2a-k have also been prepared and studied. Among the sulfonamides investigated S-N bond cleavage was found to take place over a wide range of potentials from -1.67 to -2.64 V (excluding the nitro derivative), the most acid-labile groups requiring more negative potentials, whereas this cleavage was facilitated by 0.19-0.30 V for the sulfonylcarbamates. Small scale electrolyses of 2 at controlled potential with determination of the cleavage products formed were subsequently performed. For the N-benzylbenzenesulfonamides 1, the pK(a)s in DMSO and in some cases also in water have been determined and found to be in the range 14.0-16.4 and 10.07-11.53, respectively

Mild two-step conversion of primary amides to alcohols by reduction of acylimidodicarbonates with sodium borohydride

Di-tert-butyl acylimidodicarbonates, prepared from primary amides with two equivalents of di-tert-butyl dicarbonate under catalysis by 4-dimethylaminopyridine, readily undergo selective reductive cleavage of their acyl CO-N bonds by NaBH4 to provide the corresponding alcohols in high yields.- (undefined