Epoxide opening with amino acids: improved synthesis of hydroxyethylamine dipeptide isosteres

The amino acid opening of epoxides, catalyzed by calcium trifluoromethanesulfonate with short reaction times is described. The method can be used in a straightforward route for the preparation of hydroxyethylamine dipeptide isosteres.     

Design and evaluation of dihydroxytetrahydro-1H-pyrrolo[2,1-c]- [1,4]benzothiazines as conformationally restricted transition-state inhibitors of beta-ribosidases

[structure: see text] The preparation of three new chiral thiazines from ribose is described. Two of these are dihydroxytetrahydro-1H-pyrrolo[2,1-c][1,4]benzothiazines with iminopentitol substructures corresponding to the L-lyxo and D-ribo configurations. They were designed to present a favorable transition-state mimic for the inhibition of ribosidases. This new thiazine class opens the way to the development of new inhibitors to carbohydrate processing enzymes of therapeutic importance such as nucleoside hydrolases and purine nucleoside phosphorylases.     

Synthesis of novel non-natural conformationally restricted cyclopropane amino acids of spirane series

Russian Chemical Bulletin - New conformationally rigid spirane analogues of γ-aminobutyric acid, namely, 4-aminospiro[2.2]pentanecarboxylic and 1-aminospiro[2.3]hexane-5-carboxylic acids were...     

Synthesis of alkylated sugar amino acids: conformationally restricted L-Xaa-L-Ser/Thr mimics

Two synthetic strategies for the generation of delta-substituted pyranoid sugar amino acids (SAAs) are evaluated. The first employs chiral nonracemic tert-butane sulfinamides as key reagents. Regardless of the stereochemistry of the applied sulfinamide, the product formed has a stereochemistry resembling that of a d amino acid at C7. Direct Grignard reaction on formyl-tetra-O-benzyl-beta-D-C-glucopyranoside in the second strategy and subsequent Mitsunobu inversion, yields the l,l-dipeptide isosters.     

Spirolactams as conformationally restricted pseudopeptides: synthesis and conformational analysis

The synthesis of 1-(tert-butoxycarbonyl)-7-[1-(tert-butoxycarbonyl)-3-methylbutyl]-6-oxo-1,7-diazaspiro[4.5]decanes (S,S)-1a and (S,R)-1b is described. Derivatives 17a,b and 19a are prepared for use in peptide synthesis as constrained surrogates of the Pro-Leu and Gly-Leu dipeptides. The Ac-[Gly-Leu]-Met-NH(2) derivatives (S,S,S)-2a and (S,R,S)-2b, with the tripeptidic C-terminal region present in tachykinins, are also synthesized. Conformational analyses of these tripetide analogues by NMR experiments and molecular modeling calculations show that both (S,S,S)-2a and (S,R,S)-2b epimers are gamma-turn/distorted type II beta-turn mimetics.     

Stereocontrolled synthesis of cyclopropanol amino acids from allylic sulfones: conformationally restricted building blocks

[reaction: see text] A new amino acid methyl ester with a cyclopropanol has been synthesized starting from the allyl sulfone 10. The starting material, 10, could be obtained in both enantiomeric forms. The stereoselectivity of the cyclopropane formation has been studied by molecular modeling.     

Carbohydrate-derived conformationally restricted bicyclic dipeptides as potential hetero foldamer building blocks

Starting from carbohydrate precursors, hetero foldamer building blocks featuring diverse amino acid side chains and stereochemistry have been accessed via a multi-step synthetic protocol. These conformationally restricted bicyclic dipeptide building blocks are characterized by a constrained β-lactam ring fused with a pyrrolidine ring carrying a hydroxyethylamine isostere (HEA) on the backbone. These building blocks offer the possibility of developing foldamers with interesting structural architectures, conspicuously different from those classically observed. Furthermore, such hetero-building blocks have the potential to augment the conformational space available for foldamer design with diverse backbone conformations and structural architectures.     

Simple access to novel azetidine-containing conformationally restricted amino acids by chemoselective reduction of β-lactams

Reduction with diphenylsilane and catalytic amounts of tris(triphenylphosphine)rhodium(I) carbonyl hydride resulted in an efficient, chemoselective method for the transformation of amino-acid-derived β-lactams into the corresponding azetidines, which after removal of the p-methoxybenzyl group, afforded a new family of conformationally restricted amino acids. Phe-derived compounds were obtained in enantiopure form by combining HPLC resolution of the β-lactam precursor and the above-mentioned procedure.     

Design of amino acid sulfonamides as transition-state analogue inhibitors of arginase

Arginase is a binuclear manganese metalloenzyme that catalyzes the hydrolysis of L-arginine to form L-ornithine plus urea. Chiral L-amino acids bearing sulfonamide side chains have been synthesized in which the tetrahedral sulfonamide groups are designed to target bridging coordination interactions with the binuclear manganese cluster in the arginase active site. Syntheses of the amino acid sulfonamides have been accomplished by the amination of sulfonyl halide derivatives of (S)-(tert-butoxy)-[(tert-butoxycarbonyl)amino]oxoalkanoic acids. Amino acid sulfonamides with side chains comparable in length to that of L-arginine exhibit inhibition in the micromolar range, and the X-ray crystal structure of arginase I complexed with one of these inhibitors, S-(2-sulfonamidoethyl)-L-cysteine, has been determined at 2.8 A resolution. In the enzyme-inhibitor complex, the sulfonamide group displaces the metal-bridging hydroxide ion of the native enzyme and bridges the binuclear manganese cluster with an ionized NH(-) group. The binding mode of the sulfonamide inhibitor may mimic the binding of the tetrahedral intermediate and its flanking transition states in catalysis. It is notable that the ionized sulfonamide group is an excellent bridging ligand in this enzyme-inhibitor complex; accordingly, the sulfonamide functionality can be considered in the design of inhibitors targeting other binuclear metalloenzymes.     

Design of amino acid aldehydes as transition-state analogue inhibitors of arginase

Arginase is a binuclear manganese metalloenzyme that catalyzes the hydrolysis of l-arginine to form l-ornithine and urea. Chiral L-amino acids bearing aldehyde side chains have been synthesized in which the electrophilic aldehyde C=O bond is isosteric with the C=N bond of L-arginine. This substitution is intended to facilitate nucleophilic attack by the metal-bridging hydroxide ion upon binding to the arginase active site. Syntheses of the amino acid aldehydes have been accomplished by reduction, oxidation, and Wittig-type reaction with a commercially available derivative of L-glutamic acid. Amino acid aldehydes exhibit inhibition in the micromolar range, and the X-ray crystal structure of arginase I complexed with one of these inhibitors, (S)-2-amino-7-oxoheptanoic acid, has been determined at 2.2 A resolution. In the enzyme-inhibitor complex, the inhibitor aldehyde moiety is hydrated to form the gem-diol: one hydroxyl group bridges the Mn(2+)(2) cluster and donates a hydrogen bond to D128, and the second hydroxyl group donates a hydrogen bond to E277. The binding mode of the neutral gem-diol may mimic the binding of the neutral tetrahedral intermediate and its flanking transition states in arginase catalysis.     

Pyranocyclopropanyl sugar amino acids,a new class of constrained (di)peptide isosteres

The design, synthesis and application of oxabicyclo[4.1.0]heptane amino acids as conformationally restricted sugar amino acid dipeptide isosteres are reported.     

Synthesis of (3S,5S)-3,5-diaminopiperidin-2-one as a conformationally restricted surrogate of Dab-Gly dipeptide

An efficient and stereospecific synthesis of chiral 3,5-diaminopiperidin-2-one as a novel conformationally restricted surrogate of 2,4-diaminobutanoyl (Dab)-Gly dipeptide has been achieved. The key steps include (i) ruthenium tetroxide (RuO₄) oxidation of N-Boc-2-azidomethylpyrrolidines with a catalytic amount of RuO₂·xH₂O in a two-phase system of aq NaIO₄/AcOEt and (ii) intramolecular transamidation of the resulting 2-azidomethylpyrrolidin-2-ones with 10% Pd–C in MeOH/H₂O (12/1, v/v) under an H₂ atmosphere (3 atm). This methodology represents a powerful tool for the synthesis of Dab-Gly dipeptide surrogate.     

Rhodium(II) catalyzed highly diastereoselective synthesis of conformationally restricted dispiro[1,3-dioxolane]bisoxindoles

Synthesis of conformationally restricted dispiro- and bis-dispiro-1,3-dioxolanes via three-component reaction of diazoamides, ketoamides/diketones, and aromatic/heteroaromatic aldehydes in the presence of rhodium(II) acetate dimer catalyst at room temperature involving carbonyl ylides is demonstrated with diastereoselectivity. Synthesis of macrocyclic dispiro-1,3-dioxolanes via intramolecular carbonyl ylide is also delineated in high yield. The conformationally restricted symmetrical as well as unsymmetrical dispiro-1,3-dioxolanes were obtained under mild conditions in a highly diastereo- and regioselective manner.     

Selective synthesis of conformationally restricted mono-cyclopentadienyl titanium(IV) complexes of p-tBu-calix[6]arene

Reaction of p-'Bu-calix[6]arene with potassium metal in methanol followed by [TiCp2Cl2] affords novel mononuclear and binuclear monocyclopentadienyl titanium(IV) complexes, both having the same inverted double cone conformation with a Cp in one of the cavities, in both complexes.     

Diastereoselective synthesis of (+/-)-(3-aminocyclopentane)alkylphosphinic acids, conformationally restricted analogues of GABA

A divergent synthesis of both diastereoisomers of (+/-)-(3-aminocyclopentane)alkylphosphinic acid is described. Both diastereoisomers are obtained in 5 steps from the key (+/-)-(3-hydroxycyclopent-1-ene)alkylphosphinate esters which are prepared via a palladium catalysed C-P bond forming reaction.     

Asymmetric synthesis of 4-substituted prolines as conformationally constrained amino acid analogues

Treatment of readily available chiral building block 1 with (2R)-2,3-O-isopropylideneglyceraldehyde (5) provides a new route for asymmetric synthesis of 2,4-disubstituted pyrrolidines. Several proline-amino acid chimeras: proline-leucine, proline-lysine, proline-arginine and proline-glutamic acid, are synthesized in highly diastereomerically pure forms.     

Efficient microwave-assisted synthesis of 4-amino-2-benzazepin-3-ones as conformationally restricted dipeptide mimetics

In this paper, we describe the synthesis of conformationally constrained dipeptide mimetic derivatives. Microwave flash heating was used in several synthetic steps providing the opportunity to perform the reactions in dramatically shortened time as well as to increase the obtained yields. The efficiency of the methodology makes it useful in order to prepare other dipeptides containing the 4-amino-tetrahydro-2-benzazepin-3-one motif.     

Potential DNA bis-intercalating agents: Synthesis and antitumor activity of novel,conformationally restricted bis(9-aminoacridines)

A series of bis(9-aminoacridines) bridged by conformationally restricted tethers was synthesized and evaluated against L1210 in vitro. Several of these compounds were found to be highly active in this test system, with ID₅₀ values below 10^?7 M. CPK molecular models suggest that this antitumor activity can be correlated to the ability of these bis(9-aminoacridines) to form bis-intercalative complexes with DNA.