Synthesis of (2S, 3R, 4S)-3,4-methanoproline and analogues by cyclopropylidene insertion

Reversal of polarity by catalytic SET oxidation: synthesis of azabicyclo[m.n.0]alkanes via chemoselective reduction of amidines

A one-pot catalytic method has been developed for the stereoselective synthesis of cyclopropane-fused cyclic amidines using CuBr2/K2S2O8 as an efficient single electron transfer (SET) oxidative system. The generality of this mild method is demonstrated with a wide variety of substrates to furnish pharmaceutically important amidines containing aza-bicyclic and novel aza-tricyclic frameworks in very good yields. A chemoselective reduction of cyclic amidines to 2-/3-azabicyclo[m.n.0]alkanes and octahydroindoles has been developed using a NaBH4/I2 reagent system. The synthetic scope of the chemoselective reduction of the amidine functionality has been exemplified in the stereoselective synthesis of an iminosugar based (±)-epiquinamide analogue.

Menthyl esterification allows chiral resolution for the synthesis of artificial glutamate analogs

Herein, we report the enantiospecific synthesis of two artificial glutamate analogs designed based on IKM-159, an antagonist selective to the AMPA-type ionotropic glutamate receptor. The synthesis features the chiral resolution of the carboxylic acid intermediate by the esterification with ʟ-menthol, followed by a configurational analysis by NMR, conformational calculation, and X-ray crystallography. A mice in vivo assay showed that (2R)-MC-27, with a six-membered oxacycle, is neuroactive, whereas the (2S)-counterpart is inactive. It was also found that TKM-38, with an eight-membered azacycle, is neuronally inactive, showing that the activity is controlled by the ring C.

Formation of Olefins by Eliminative Dimerization and Eliminative Cross-Coupling of Carbenoids: A Stereochemical Exercise

Two carbenoids combine to generate an olefin by a mechanism involving formation of an ate complex, 1,2-metalate rearrangement, and β-elimination. As each stage of this eliminative coupling is stereospecific, the overall stereochemical outcome can be understood and, in principle fully controlled, providing that the absolute stereochemical configurations of the reacting carbenoid species are defined. In contrast to traditional alkene syntheses, the eliminative cross-coupling of carbenoids offers a connective approach to olefins capable of precisely targeting a given isomer regardless of the nature of the features distinguishing the isomers. The formation of olefins by the eliminative dimerization and eliminative cross-coupling of carbenoids is reviewed with a range of illustrative examples, including the reactions of α-lithiated haloalkanes, epoxides, and carbamates. An emphasis is placed on stereochemical analysis and methods to generate sp³ -hybridized carbenoids in stereodefined form are surveyed.

Estimation of optical rotation of γ-alkylidenebutenolide, cyclopropylamine, cyclopropyl-methanol and cyclopropenone based compounds by a Density Functional Theory (DFT) approach

Computing the optical rotation of organic molecules can be a real challenge, and various theoretical approaches have been developed in this regard. A benchmark study of optical rotation of various classes of compounds was carried out by Density Functional Theory (DFT) methods. The aim of the present research study was to find out the best-suited functional and basis set to estimate the optical rotations of selected compounds with respect to experimental literature values. Six DFT functional LSDA, BVP86, CAM-B3LYP, B3PW91, and PBE were applied on 22 different compounds. Furthermore, six different basis sets, i.e., 3-21G, 6-31G, aug-cc-pVDZ, aug-cc-pVTZ, DGDZVP, and DGDZVP2 were also applied with the best-suited functional B3LYP. After rigorous effort, it can be safely said that the best combination of functional and basis set is B3LYP/aug-cc-pVTZ for the estimation of optical rotation for selected compounds.

Synthesis and conformational analysis of peptides embodying 2,3-methanopipecolic acids

When 2,3-methanopipecolic acids replace a proline in peptides, a marked preference (42–92%) for thecisgeometry around the pipecolic amide bond is observed in both water and organic solvents.

An Access to 3,4-(Aminomethano)proline in Racemic and Enantiomerically Pure Form

Protected racemic and enantiomerically pure 3,4-(aminomethano)prolines rac-9 and (2S,2'R,3R,4R)-9 have been prepared applying a titanium-mediated reductive cyclopropanation as a key step. Thus, cyclopropanations of N,N-dibenzylformamide with titanacyclopropanes generated in situ from racemic or enantiomerically pure tert-butyl N-Boc-3,4-dehydroprolinates rac-8 or (S)-8 proceed diastereoselectively, and furnish the protected racemic and enantiomerically pure diamino acid 9. The latter was incorporated into three tripeptides containing glycyl, alanyl and phenylalanyl moieties.

Synthesis of Novel Potent Dipeptidyl Peptidase IV Inhibitors with Enhanced Chemical Stability: Interplay between the N-Terminal Amino Acid Alkyl Side Chain and the Cyclopropyl Group of α-Aminoacyl-l-cis-4,5-methanoprolinenitrile-Based Inhibitors

A series of methanoprolinenitrile-containing dipeptide mimetics were synthesized and assayed as inhibitors of the N-terminal sequence-specific serine protease dipeptidyl peptidase IV (DPP-IV). The catalytic action of DPP-IV is the principle means of degradation of glucagon-like peptide-1, a key mediator of glucose-stimulated insulin secretion, and DPP-IV inhibition shows clinical benefit as a novel mechanism for treatment of type 2 diabetes. However, many of the reversible inhibitors to date suffer from chemical instability stemming from an amine to nitrile intramolecular cyclization. Installation of a cyclopropyl moiety at either the 3,4- or 4,5-position of traditional 2-cyanopyrrolidide proline mimetics led to compounds with potent inhibitory activity against the enzyme. Additionally, cis-4,5-methanoprolinenitriles with beta-branching in the N-terminal amino acid provided enhanced chemical stability and high inhibitory potency. This class of inhibitors also exhibited the ability to suppress prandial glucose elevations after an oral glucose challenge in male Zucker rats.