D. Tourwe

Synthesis of 3,3-dimethylazetidine-2-carboxylic acid and some derivatives

Abstract γ-Chloro-α-(N-alkylimino)esters were reduced by sodium cyanoborohydride in methanol in the presence of acetic acid with complete selectivity to give rise to either γ-chloro-α-(N-alkylamino)esters (reaction at 0°C) or 1-alkyl-3,3-dimethylazetidine-2-carboxylic esters (reaction at reflux). The isolable γ-chloro-α-(N-alkylamino)esters are suitable sources for 1-(N-alkylamino)-2,2-dimethylcyclopropane-1-carboxylic esters via base-induced 1,3-dehydrochlorination, while the former substrates as transient species undergo 1,4-dehydrochlorination to the corresponding azetidines. The latter process was used for the synthesis of 3,3-dimethylazetidine-2-carboxylic acid, a new non-proteinogenic sterically hindered α-amino acid, via hydrogenolysis of methyl 1-benzyl-3,3-dimethylazetidine-1-carboxylate and subsequent acidic hydrolysis. Reduction of alkyl 4-chloro-3,3-dimethyl-α-(N-alkylimino)butanoates with lithiumaluminiumhydride in diethyl ether afforded 1-alkyl-3,3-dimethyl-2-(hydroxymethyl)-azetidines.

Syntheses and reactions of 1-amino-2,2-dialkylcyclopropane-1-carbonitriles and -carboxamides - Potential precursors of ACC derivatives

The direct cyclization of 2-amino-4-chloro-3,3-dimethylbutanenitrile with potassium tert-butoxide in THF afforded 1-amino-2,2-dimethylcyclopropane-1-carbonitrile and a dimerization product. Various new cis- and trans-1-(teri-butylamino)-2-benzyl- 2-methylcyclopropane-carbonitriles and the corresponding cyclopropanecarboxamides have been synthesized, with focus on the isolation of the pure stereoisomeric cyclopropanecarboxamides. The relative configuration of the stereoisomers was established by X-ray crystallographic analysis of one of the model compounds. A new route to the latter functionalized cyclopropanes was developed by reaction of 1-methoxycyclopropylamines with potassium cyanide. Some remarkable rearrangements of 1-aminocyclopropane-1-carbonitriles into azetidine and oxazine derivatives via Favorskii-derived intermediates are reported. Various aspects of the chemistry of geminally functionalized cyclopropanes are discussed.

Somatostatin analogues containing o-aminomethylphenylacetic acid as a bridge unit

A new cis-peptide bond mimetic, α-benzyl-o-aminomethylphenylacetic acid, was synthesized and incorporated in a homodetic somatostatin analogue. Biological binding tests and 2D NMR conformational analysis indicate that the configuration of the bridge-unit asymmetric center and the orientation of the benzyl side chain play a key role in the biological activity of this type of somatostatin analogues.

Conformation-directed design of cyclic somatostatins containing a βVI-turn mimetic

The design process and the synthetic problems for the construction of conformationally constrained cyclic somatostatins are described. Highly potent analogs containing o-aminomethylphenylacetic acid or o-aminomethylphenylalanine are obtained.

Synthesis of the diastereomers of β-Me-Tyr and β-Me-Phe and their effect on the biological properties of the delta opioid receptor antagonist TIPP

In order to influence side-chain conformations and to increase the μ-agonist properties of the δ-selective opioid receptor δ-antagonist H-Tyr-Tic-Phe-Phe-NH2, residues Tyr1, Phe3 and Phe4 were replaced by their β-methyl-substituted stereoisomers. Synthesis of β-Me-Tyr was carried out in a stereoselective way. Incorporation of the modified amino acids was performed by SPPS. Receptor binding data and GPI and MVD bioassays were obtained for all stereoisomers, in general showing equal or slightly increased potencies. In the [(R,S)β-Me-Phe3]analogue, the introduction of the β-methyl substituent restores signal transduction.

New methods for solid phase peptide synthesis of transitionstate analog inhibitors of HIV-1 protease and DPP-IV

A new and stereoselective method to synthesize hydroxyethylamine and hydroxymethylamide peptide bond isosteres is developed. The key step is the addition of 2-trimethylsilylthiazole to α-aminoaldehydes, followed by transformation to α-hydroxy-β-aminoaldehydes. The stereochemistry of the addition can be manipulated by the choice of the nitrogen substitution. The isosteres are easily synthesized via Solid Phase Peptide Synthesis, which rapidly gives the desired pseudopeptides.