Reactions of thioamides with metal carboxylates in organic media

Arynes Promoted Dehydrosulfurization of Thioamides: Access to Nitriles and Diaryl Sulfides

An aryne-promoted dehydrosulfurization reaction of thioamides to give nitriles and diaryl sulfides in a one-pot manner is presented. Aromatic, heteroaromatic, and aliphatic natural products and drug-derived nitriles and diaryl sulfides were obtained in good to excellent yields. Especially, selenoamide was also a suitable substrate and produced diaryl selenide and nitrile in high yields. The D-labeled experiments indicated that the protons of thioamides transfer to diaryl sulfides.

Chemo- and Site-Selective Replacement of N-Terminal Carbamates in Peptides

In peptide synthesis, it is important to distinguish the terminal amino group and carry out the selective transformation of only the N-terminal protecting group. We describe herein a reaction for the chemo- and site-selective replacement of carbamates with various other carbamates only at the N-terminus of peptides. We demonstrate the scope of carbamates and peptides and the introduction of fluorine into a peptide. This strategy is applicable to the late stage of peptide synthesis.

Synthesis of Nitriles via the Iodine-Mediated Dehydrosulfurization of Thioamides

A simple general method for the synthesis of nitriles using the inexpensive and easy to handle iodine (I₂) is described herein. The reaction of thioamides with I₂ in the presence of triethylamine at room temperature under aerobic conditions afforded various nitriles bearing aryl, vinyl, and alkyl groups in good-to-excellent yields. This method was also effective for conversion from thioureas to cyanamides.

Ring Expansion of Thiolactams via Imide Intermediates: An Amino Acid Insertion Strategy

The Ag^I -promoted reaction of thiolactams with N-Boc amino acids yields an N-(α-aminoacyl) lactam that can rearrange through an acyl transfer process. Boc-deprotection results in convergence to the ring-expanded adduct, thereby facilitating an overall insertion of an amino acid into the thioamide bond to generate medium-sized heterocycles. Application to the site-specific insertion of amino acids into cyclic peptides is demonstrated.

Metal-free dehydrosulfurization of thioamides to nitriles under visible light

A visible light-mediated dehydrosulfurization of thioamides to nitriles is demonstrated, using an organic dye as a photocatalyst and air as an oxidant.

Nonclassical Routes for Amide Bond Formation

The present review offers an overview of nonclassical (e.g., with no pre- or in situ activation of a carboxylic acid partner) approaches for the construction of amide bonds. The review aims to comprehensively discuss relevant work, which was mainly done in the field in the last 20 years. Organization of the data follows a subdivision according to substrate classes: catalytic direct formation of amides from carboxylic and amines ( section 2 ); the use of carboxylic acid surrogates ( section 3 ); and the use of amine surrogates ( section 4 ). The ligation strategies (NCL, Staudinger, KAHA, KATs, etc.) that could involve both carboxylic acid and amine surrogates are treated separately in section 5 .

Synthesis of Peptides by Silver-Promoted Coupling of Carboxylates and Thioamides: Mechanistic Insight from Computational Studies

The mechanism of the recently described N→C direction peptide synthesis through silver-promoted coupling of N-protected amino acids with thioacetylated amino esters was explored by using density functional theory. Calculation of the potential energy surfaces for various pathways revealed that the reaction proceeds through silver-assisted addition of the carboxylate to the thioamide, which is followed by deprotonation and silver-mediated extrusion of sulfur as Ag2 S. The resulting isoimide is the key intermediate, which subsequently rearranges to an imide through a concerted pericyclic [1,3]-acyl shift (O-sp(2) N 1,3-acyl migration). The proposed mechanism clearly emphasises the requirement of two equivalents of Ag(I) and basic reaction conditions, which is in full agreement with the experimental findings. Alternative rearrangement pathways involving only one equivalent of Ag(I) or through O-sp(3) N 1,3-acyl migration can be excluded. The computations further revealed that peptide couplings involving thioformamides require significant conformational changes in the intermediate isoformimide, which slow down the rearrangement process.

Steric and Electronic Effects in the Synthesis and Regioselective Hydrolysis of Unsymmetrical Imides

The AgI-promoted coupling reaction of thioamides and carboxylic acids is shown to be a useful method for the generation of unsymmetrical imides. The reaction proceeds efficiently with unhindered and electron-rich or neutral coupling partners, but not with hindered thioamides (such as thiopivalamides) or electron deficient thioamides (such as trifluorothioacetamides). Intriguingly, thioformamides are also ineffective coupling partners, despite having minimal steric or electronic influence. Hindered carboxylic acid coupling partners (such as pivalic acid) are tolerated, but electron deficient acids, such as trifluoroacetic acid, are ineffective coupling partners. Furthermore, an interplay of both steric and electronic effects is observed in the subsequent hydrolysis of unsymmetrical imides. Imides with a dimethoxybenzoyl group give high regioselectivity upon hydrolysis, favouring cleavage of the distal acyl group. Imides with a p-nitrobenzoyl or pivaloyl group give reversed selectivity, favouring cleavage of the proximal acyl group.

Alkenes as Chelating Groups in Diastereoselective Additions of Organometallics to Ketones

Alkenes have been discovered to be chelating groups to Zn(II), enforcing highly stereoselective additions of organozincs to β,γ-unsaturated ketones. ¹H NMR studies and DFT calculations provide support for this surprising chelation mode. The results expand the range of coordinating groups for chelation-controlled carbonyl additions from heteroatom Lewis bases to simple C–C double bonds, broadening the 60 year old paradigm.

A new method for peptide synthesis in the N→C direction: amide assembly through silver-promoted reaction of thioamides

The Ag(i)-promoted coupling of peptide-acids with thioamides generates peptide-imides, which was exploited in the synthesis of peptides in the N→C direction.

Synthesis and Pharmacological in Vitro and in Vivo Evaluations of Novel Triazole Derivatives as Ligands of the Ghrelin Receptor. 1

A new series of growth hormone secretagogue (GHS) analogues based on the 1,2,4-triazole structure were synthesized and evaluated for their in vitro binding and their ability to stimulate intracellular calcium release to the cloned hGHS-1a ghrelin receptor expressed in LLC PK-1 cells. We have synthesized potent ligands of this receptor, some of them behaving as agonists, partial agonists, or antagonists. Some compounds among the most potent, i.e., agonist 29c (JMV2873), partial agonists including 21b (JMV2810), antagonists 19b (JMV2866) and 19c (JMV2844), were evaluated for their in vivo activity on food intake, after sc injection in rodents. Some compounds were found to stimulate food intake like hexarelin; some others were identified as potent hexarelin antagonists in this assay. Among the tested compounds, 21b was identified as an in vitro ghrelin receptor partial agonist, as well as a potent in vivo antagonist of hexarelin-stimulated food intake in rodents. Compound 21b was without effect on GH release from rat. However, in this series of compounds, it was not possible to find a clear correlation between in vitro and in vivo results.

Solution and solid-supported synthesis of 3,4,5-trisubstituted 1,2,4-triazole-based peptidomimetics

[reaction: see text] 3,4,5-Trisubstituted 1,2,4-triazoles were synthesized in solution from various thioamides and hydrazides in smooth experimental conditions leading to peptidomimetic scaffolds. This strategy was found to be compatible with the usual peptide synthesis protecting groups. This methodology was then applied on solid support by anchoring alpha-amino acids through their amino function to an activated carbonate resin.

A general synthetic method for the formation of substituted 5-aminotetrazoles from thioureas: a strategy for diversity amplification

A general method for the synthesis of 5-aminotetrazoles is outlined using the mercury(II)-promoted attack of azide anion on a thiourea. The reaction proceeds through a guanyl azide intermediate, which undergoes electrocyclization to the tetrazole. The method is high yielding and provides access to mono-, di-, and trisubstituted 5-aminotetrazoles, targets of potential interest for combinatorial library development.