Synthesis of di- and tripeptide analogues containing alpha-ketoamide as a new core structure for inhibition of HIV-1 protease

Practice of green chemistry strategies in synthetic organic chemistry: a glimpse of our sincere efforts in green chemistry research

This feature article summarises our recent contributions (2019-2023) in designing and developing a handful of promising organic transformations for accessing several diversely functionalised biologically relevant organic scaffolds, following the green chemistry principles, particularly focusing on the application of low-energy visible light, electrochemistry, ball-milling, ultrasound, and catalyst- and additive-free synthetic strategies.

Electrochemical Formation of α-Ketoamides from Ketoximes through Non-Beckmann Mechanism Pathway

α-Ketoamides are highly valued in synthetic chemistry due to their incorporation into diverse natural products and drug molecules. Here, we present an innovative electrochemical approach for constructing α-ketoamides, utilizing a mild and environmentally friendly strategy in a user-friendly undivided cell setup under constant current. The excellent functional-group tolerance, convenient accessibility of reaction instruments and starting materials, and easy scalability collectively enhance the importance of this protocol compared to previous challenging methods. Additionally, mechanistic insight into this reaction is obtained through the investigation of cyclic voltammograms of the reactants.

Pseudoprolines as stereoelectronically tunable proline isosteres

The cyclic structure of proline (Pro) confers unique conformational properties on this natural amino acid that influences polypeptide structure and function. Pseudoprolines are a family of Pro isosteres that incorporate a heteroatom, most prominently oxygen or sulfur but also silicon and selenium, to replace the C_β or C_γ carbon atom of the pyrrolidine ring. These readily synthetically accessible structural motifs can facilitate facile molecular editing in a fashion that allows modulation of the amide bond topology of dipeptide elements and influence over ring pucker. While the properties of pseudoprolines have been exploited most prominently in the design of oligopeptide analogues, they have potential application in the design and optimization of small molecules. In this Digest, we summarize the physicochemical properties of pseudoprolines and illustrate their potential in drug discovery by surveying examples of applications in the design of bioactive molecules.

Selective amidation by a photocatalyzed umpolung reaction

Herein, a metal-catalyzed organic transformation merged with another organophotocatalyst has been developed under mild conditions for the production of α-ketoamides.

Electrochemical synthesis of 1,2-diketones from alkynes under transition-metal-catalyst-free conditions

A novel electrochemical protocol for the direct oxidation of internal alkynes in air to provide 1,2-diketones was developed.

Copper-catalyzed coupling of anthranils and α-keto acids: direct synthesis of α-ketoamides

Copper-catalyzed coupling of α-keto acids with anthranils is reported for the synthesis of α-ketoamides bearing an aldehyde group via N–O/C–O bond cleavages and C–N bond formation.

Cu(i)-Functionalized SBA-16: an efficient catalyst for the synthesis of α-ketoamides under moderate conditions

An efficient catalyst based on the cage-like mesoporous material SBA-16 as the support and Cu(i) as active sites has been successfully prepared. The catalyst demonstrated high catalytic activity (up to 88%) in the direct oxidative synthesis of α-ketoamides between acetophenone and piperidine, employing O2 from open air as the oxidant without other additives. A heterogeneous catalyst was applied in this reaction for the first time, and the catalyst could be easily separated from the reaction system by filtration and reused several times without a significant loss of activity.

Copper–TEMPO-catalyzed synthesis of α-ketoamides via tandem sp3C–H aerobic oxidation and amination of phenethyl alcohol derivatives

The first synthesis of α-ketoamides from phenethyl alcohol derivatives, simple and readily available substrates, was achieved.

A two-step continuous synthesis of α-ketoamides and α-amino ketones from 2° benzylic alcohols using hydrogen peroxide as an economic and benign oxidant

A practical two-step flow synthesis of α-ketoamides and α-amino ketones via direct oxidative coupling between 2° benzylic alcohols and amines was developed.

Metal free one-pot synthesis of α-ketoamides from terminal alkenes

A practical approach towards the synthesis of α-ketoamides from terminal alkenes has been developed using I₂/IBX under one-pot reaction conditions.

A general metal free approach to α-ketoamides via oxidative amidation–diketonization of terminal alkynes

A metal free catalytic system employing TMSOTf/I₂/DMSO for the oxidative amidation–diketonization of terminal alkynes, in order to produce a wide variety of α-ketoamides, has been developed.

Metal-free in situ sp3, sp2, and sp C–H functionalization and oxidative cross coupling with benzamidines hydrochloride: a promising approach for the synthesis of α-ketoimides

A new metal-free tandem protocol for the synthesis of α-ketoimides via sp³, sp², and sp C–H functionalization followed by oxidative cross coupling with benzamidines hydrochloride using catalytic iodine with TBHP in DMSO has been developed.

Pseudo five-component synthesis of bis-alpha-acyloxy-beta-diketo amides from diimide-dicarboxylic acids

Diimide-dicaboxylic acids derived from condensation of alpha-amino acids with the 2,3,5,6-bicyclo[2.2.2] oct-2-enetetracarboxylic-2,3:5,6-dianhydride or 1,2,4,5- bezenetetracarboxylic-1,2:4,5-dianhydride react with ninhydrin and isocyanides to produce some novel interesting bis-alpha-acyloxy-beta-diketo amides.

Peptide inhibition of HIV-1: current status and future potential

More than 2 decades of intensive research has focused on defining replication mechanisms of HIV type 1 (HIV-1), the etiologic agent of AIDS. The delineation of strategies for combating this viral infection has yielded many innovative approaches toward this end. HIV-1 is a lentivirus in the family retroviridae that is relatively small with regard to both structure and genome size, having a diploid RNA genome of approximately 9 kb, with only three major genes and several gene products resulting from alternate splicing and translational frameshifting. Most marketed drugs for treating AIDS are inhibitors of HIV-1 reverse transcriptase or protease enzymes, but new targets include the integrase enzyme, cell surface interactions that facilitate viral entry, and also virus particle maturation and assembly. The emergence of drug-resistant variants of HIV-1 has been the main impediment to successful treatment of AIDS. Thus, there is a pressing need to develop novel treatment strategies targeting multiple stages of the virus life-cycle. Research efforts aimed at developing successful means for combating HIV-1 infection have included development of peptide inhibitors of HIV-1. This article summarizes past and current endeavors in the development of peptides that inhibit replication of HIV-1 and the role of peptide inhibitors in the search for new anti-HIV drugs.

Anisotropic and hydrogen bonding effects in phenylglyoxamides and mandelamides: theoretical and NMR conformational evaluation

Interesting anisotropic effects were observed for phenylglyoxamides and their respective mandelamides. Such effects were observed in experimental (1)H and (13)C NMR (in CDCl(3), CD(3)OD, and DMSO-d(6) solvents) and in some cases with good correlation to theoretical (1)H and (13)C NMR DFT-GIAO (B3LYP/6-311++G**//B3LYP/6-31G*) calculations. A systematic conformational analysis of these compounds was performed in a two-step methodology, using PM3 and DFT (B3LYP/6-31G*) calculations; with good accomplishment and computational time economy. It was observed that intramolecular hydrogen bonding plays a significant role in the conformation of such compounds. Finally, a geminal nonequivalence of an N-CH(2) moiety, in one of the alkyl side chain (R1 = R2), was found for the tertiary mandelamides studied.

A Novel Dipeptide-based HIV Protease Inhibitor Containing Allophenylnorstatine

Dipeptide analogues incorporating allophenylnorstatine [Apns; (2S,3S)-3amino-2-hydroxy-4-phenylbutyric acid] as a transition state mimic at the scissile bond were designed and synthesized in the hope of obtaining a novel KNI series of HIV protease inhibitors. The precursors, N-P2'-3-(2S,3S)-3-(tert-butyloxy-carbonyl)amino-2-hydroxy-4-phenylbutanoyl)-5,5-dimethylthiazolidine-4-carboxamide (N-Boc-Apns-Dmt-P2') 4a-p were prepared by deprotection of the synthones N-P2'-(tert-butyloxycarbonyl)-5,5-dimethylthiazolidine-4-carboxamide (Boc-Dmt-P2') 2a-p, then coupling with (2S,3S)3-(tert-butyloxycarbonyl)amino-2-hydroxy-4-phenylbutanoic acid (N-Boc-Apns-OH) 3. The deprotected intermediates 4 were coupled with the activated carboxyl groups of the P2 ligands to afford the target dipeptides. In this work, we fixed at the P2 site either a 2,6-dimethylphenoxyacetyl or a 3-hydroxy-2-methylbenzoyl group. Substitutes at the P2' site were varied to afford the members of the series 7 and 8. Improved activity of most of the members of series 8 relative to their analogues of series 7 can be partially attributed to the differences in the structures of the P2 moieties. Positional isomerism in the P2' moieties significantly affected the activity and polarity of the target.

Alpha-keto amide peptides: a synthetic strategy to resin-bound peptide isosteres for protease inhibitor screening on solid support

A synthetic strategy for the formation of resin-bound internal alpha-keto amide peptides suitable for protease inhibitor screening on solid support is presented. This general approach is based on the incorporation of alpha-keto amide building blocks during solid-phase peptide synthesis (SPPS). Such dipeptidyl building blocks were accessible using the acylcyanophosphorane methodology. The acid-labile alpha-keto carbonyl functionality was protected as a 1,3-dithiolane derivative. This protective group is fully compatible with standard SPPS reaction conditions and can be efficiently removed with N-bromosuccinimide in 10% aqueous acetone. The alpha-keto amide peptides were assembled on SPOCC-1500 resin and were characterized with high-resolution magic angle spinning (HR-MAS) NMR on bead. The methodology was evaluated and tested with a variety of building blocks containing natural and nonnatural amino acid moieties.

Correlation between the predicted and the observed biological activity of the symmetric and nonsymmetric cyclic urea derivatives used as HIV-1 protease inhibitors. A 3D-QSAR-CoMFA method for new antiviral drug design

The predicted inhibition constant (Ki) and the predicted inhibitor concentration (IC90) of the HIV-1 protease (HIV- 1 PR) inhibitors: symmetric and nonsymmetric - benzyl, ketone, oxime, pyrazole, imidazole, and triazole cyclic urea derivatives, were obtained by the 3D-CoMFA (Comparative Molecular Field Analysis) method. The CoMFA statistical parameters: cross-validate correlation coefficient (q2), higher than 0.5, and the fitted correlation coefficient (r2), higher than 0.90 validated the predicted biological activities. The best predictions were found for the trifluoromethyl ketoxime derivative (log 1/Ki predict = 8.42), the m-pyridineCH2 pyrazole derivative (log 1/Ki predict = 9.77) and the 1,2,3 triazole derivative (log 1/Ki predict = 7.03). We attempted to design a new potent HIV-1 protease inhibitor by addition of o-benzyl to the (p-HOPhCH2) pyrazole 12f derivative inhibitor. A favorable steric area surrounded the o-benzyl, suggesting a possible new potent HIV-1 protease inhibitor.