One-Pot Syntheses of Dissymmetric Diamides Based on the Chemistry of Cyclic Monothioanhydrides. Scope and Limitations and Application to the Synthesis of Glycodipeptides

Deprotective Functionalization: A Direct Conversion of Nms-Amides to Carboxamides Using Carboxylic Acids

The nature of protecting group chemistry necessitates a deprotection step to restore the initially blocked functionality prior to further transformation. As this aspect of protecting group manipulation inevitably adds to the step count of any synthetic sequence, the development of methods enabling simultaneous deprotection and functionalization ("deprotective functionalization"-distinct from "deprotection followed by functionalization") is appealing, as it has the potential to improve efficiency and streamline synthetic routes. Herein, we report a deprotective functionalization of the newly introduced Nms-amides guided by density functional theory (DFT) analysis, which exploits the inherent Nms reactivity. Mechanistic studies further substantiate and help rationalize the exquisite reactivity of Nms-amides, as other commonly used protecting groups are shown not to exhibit the same reactivity patterns. The practicality of this approach was ultimately demonstrated in selected case studies.

Intermolecular Diels-Alder Cycloadditions of Furfural-Based Chemicals from Renewable Resources: A Focus on the Regio- and Diastereoselectivity in the Reaction with Alkenes

A recent strong trend toward green and sustainable chemistry has promoted the intensive use of renewable carbon sources for the production of polymers, biofuels, chemicals, monomers and other valuable products. The Diels-Alder reaction is of great importance in the chemistry of renewable resources and provides an atom-economic pathway for fine chemical synthesis and for the production of materials. The biobased furans furfural and 5-(hydroxymethyl)furfural, which can be easily obtained from the carbohydrate part of plant biomass, were recognized as "platform chemicals" that will help to replace the existing oil-based refining to biorefining. Diels-Alder cycloaddition of furanic dienes with various dienophiles represents the ideal example of a "green" process characterized by a 100% atom economy and a reasonable E-factor. In this review, we first summarize the literature data on the regio- and diastereoselectivity of intermolecular Diels-Alder reactions of furfural derivatives with alkenes with the aim of establishing the current progress in the efficient production of practically important low-molecular-weight products. The information provided here will be useful and relevant to scientists in many fields, including medical and pharmaceutical research, polymer development and materials science.

Direct Synthesis of Diamides from Dicarboxylic Acids with Amines Using Nb2O5 as a Lewis Acid Catalyst and Molecular Docking Studies as Anticancer Agents

Several Lewis and Bronsted acid catalysts were tested for the synthesis of some targeted diamides with anticancer activity from dicarboxylic acids and amines under the same reaction condition. Among those catalysts, Nb₂O₅ showed the highest catalytic activity to the corresponding diamides. Nb₂O₅ shows water- and base-tolerant properties for which it gives the highest yield of the synthesized products. Here, we present a novel and sustainable method for the direct synthesis of diamides with anticancer activity using a reusable heterogeneous catalyst Nb₂O₅. A molecular docking study was performed for all of the synthesized compounds with various therapeutical targets of cancer and found that the human epidermal growth factor receptor (HER2) has shown a significant dock score for our synthesized products. After obtaining the best pose from molecular docking, the complex is used for molecular dynamics study by running simulations for 10 ns. The root-mean-square deviations (RMSDs) of α carbon atoms of all systems are analyzed to detect their stability. This method is effective for the direct synthesis of diamides as anticancer agents from dicarboxylic acids and amines using Nb₂O₅ as a base-tolerant heterogeneous catalyst.

A Tripeptide Approach to the Solid-Phase Synthesis of Peptide Thioacids and N-Glycopeptides

A general and robust method for the incorporation of aspartates with a thioacid side chain into peptides has been developed. Pseudoproline tripeptides served as building blocks for the efficient fluorenylmethyloxycarbonyl (Fmoc) solid‐phase synthesis of thioacid‐containing peptides. These peptides were readily converted to complex N‐glycopeptides by using a fast and chemoselective one‐pot deprotection/ligation procedure. Furthermore, a novel side reaction that can lead to site‐selective peptide cleavage using thioacids (CUT) was discovered and studied in detail.

2,4-Dinitrobenzenesulfonamide-Directed SN2-Type Displacement Reaction Enables Synthesis of β-d-Glycosaminosides

An efficient protocol to construct β-d-gluco-/galactosaminosyl linkages was established using nonparticipating and strong electron-withdrawing C-2-2,4-dinitrobenzenesulfonamide (DNsNH)-directed S_N2-like glycosylation of glycosyl ortho-hexynylbenzoates. The reaction is applicable to a wide range of O-, N-, and C-nucleophiles and features convenient conversion of DNsNH into AcNH in high yield under mild conditions. Oligomerization-ready trisaccharide, composed of β-d-(1→3)-glucosamino residues, has been achieved, setting a solid foundation for the synthesis of oligosaccharides associated with Neisseria meningitidis capsular polysaccharide.

Thioacids – synthons for amide bond formation and ligation reactions: assembly of peptides and peptidomimetics

The synthesis of α-amino thioacids and peptide thioacids and their applications in chemoselective amide bond formation, ligation of peptides/proteins/glycopeptides and synthesis of peptidomimetics are reviewed.

Obstacles and solutions for chemical synthesis of syndecan-3 (53-62) glycopeptides with two heparan sulfate chains

Proteoglycans play critical roles in many biological events. Due to their structural complexities, strategies towards synthesis of this class of glycopeptides bearing well-defined glycan chains are urgently needed. In this work, we give the full account of the synthesis of syndecan-3 glycopeptide (53-62) containing two different heparan sulfate chains. For assembly of glycans, a convergent 3+2+3 approach was developed producing two different octasaccharide amino acid cassettes, which were utilized towards syndecan-3 glycopeptides. The glycopeptides presented many obstacles for post-glycosylation manipulation, peptide elongation, and deprotection. Following screening of multiple synthetic sequences, a successful strategy was finally established by constructing partially deprotected single glycan chain containing glycopeptides first, followed by coupling of the glycan-bearing fragments and cleavage of the acyl protecting groups.

α-Methylphenacyl thioesters as convenient thioacid precursors

α-Methylphenacyl (Mpa) thioesters are described as precursors of thioacids.

Mixed-phase synthesis of glycopeptides using a N-peptidyl-2,4-dinitrobenzenesulfonamide-thioacid ligation strategy

A strategy for the solid phase peptide synthesis (SPPS) and coupling of N-peptidyl and N-glycopeptidyl 2,4-dinitrobenzenesulfonamides (dNBS) with C-terminal peptidyl thioacids has been developed. The resulting N-dDNBS peptides were coupled to generate longer peptides. Ligation reactions were complete within 15 to 20 min.

Cyclic peptide synthesis with thioacids

C-Terminal amino acid 9-fluorenylmethylthioesters may be carried through Boc chemistry solution phase peptide synthesis sequences. After insertion of the final residue in the form of an Fmoc carbamate, treatment with piperidine releases a seco-peptide as a C-terminal thioacid that on treatment with Sanger's reagent undergoes cyclization to a cyclic peptide. Cyclic penta- and hexapeptides have been synthesized in this manner, as has a cyclic glycopeptide. Functional group compatibility with alcohols and carboxylic acids is demonstrated.

Dihydro-3-(triphenylphosphoranylidene)-2,5-thiophendione: A Convenient Synthon for the Preparation of Substituted 1,4-Thiazepin-5-ones and Piperidinones via the Intermediacy of Thioacids

Reaction of thiomaleic anhydride with triphenylphosphine gives the title compound which undergoes reaction with a variety of aldehydes to give a range of alkylidene thiomaleic anhydrides (substituted monothio itaconic anhydrides). Subsequent treatment with tert-butoxycarbonylamino-substituted thiols, or under radical conditions with tert-butoxycarbonylamino-substituted alkyl halides results in a series of substituted monothiomaleic anhydrides, that on exposure to trifluoroacetic acid and then base lead to thiocarboxyl substituted 1,4-thiazepin-5-ones and piperidinones, respectively, that are ultimately trapped by reaction with 2,4-dinitrobenzenesulfonamides to give the corresponding amides.

Recent progress in the field of neoglycoconjugate chemistry

Glycosylation is probably the most complex secondary gene event that affects the vast majority of proteins in nature resulting in the occurrence of a heterogeneous mixture of glycoforms for a single protein. Many functions are exerted by single monosaccharides, well-defined oligosaccharides, or larger glycans present in these glycoproteins. To unravel these functions it is of the utmost importance to prepare well-defined single glycans conjugated to the underlying aglycon. In this review, the most recent developments are described to address the preparation of carbohydrate-amino acid (glyco-conjugates). Naturally occurring N- and O-linked glycosylation are described and the preparation of non-natural sugar-amino acid linkages are also included.

Thiomaleic anhydride: a convenient building block for the synthesis of alpha-substituted gamma- and delta-lactones through free-radical addition, nucleophilic ring opening, and subsequent thiocarboxylate manipulation

Iodoalkyl tert-butyl carbonates and carbamates undergo clean free-radical addition to thiomaleic anhydride to give substituted thiosuccinic anhydrides in high yield on treatment with tris(trimethylsilyl)silane and a radical initiator. After removal of the tert-butyloxycarbonyl group, cyclization then affords lactones or lactams substituted in the alpha-position by a thiocarboxylic acid residue. This group is converted to amides through reaction with electron-deficient sulfonamides or to aldehydes and/or ketones by the reaction of derived thioesters with either thiophenol, an electron-deficient allyl phenyl sulfide, or phenylboronic acid.

Reaction of thioacids with isocyanates and isothiocyanates: a convenient amide ligation process

Thiocarboxylates, prepared conveniently by cleavage of 9-fluorenylmethyl or trimethoxybenzyl thioesters, react at room temperature with isocyanates and isothiocyanates to give amide bonds in good to excellent yield. A carboxylate salt is also shown to react with an electron-deficient isocyanate to give the corresponding amide in excellent yield at room temperature.