Development of a Process for Triazine-Promoted Amidation of Carboxylic Acids

TCT-mediated click chemistry for the synthesis of nitrogen-containing functionalities: conversion of carboxylic acids to carbamides, carbamates, carbamothioates, amides and amines

Here, we report a s-trichlorotriazine (TCT, also known as cyanuric chloride) mediated one-pot general method for the conversion of carboxylic acids into ubiquitous functionalities such as carbamides, carbamates, carbamothioates, amides, and amines. The TCT-mediated activation of acids followed by azidation and heating led to the isocyanate formation via Curtius rearrangement which involves click chemistry in the presence of nucleophiles and provided the coupled product. The TCT was employed at ≤40 mol% with respect to the starting materials; however, its bulk availability and low cost provide a unique opportunity towards its applicability in the synthesis of functional molecules. The optimized conditions have also been successfully demonstrated for gram scale synthesis and late-stage functionalization of natural products and drugs such as podophyllotoxin, eugenol, diosgenin, geraniol and fluvoxamine.

Rapid Organocatalytic Formation of Carbon Monoxide: Application towards Carbonylative Cross Couplings

Herein, the first organocatalytic method for the transformation of non‐derivatized formic acid into carbon monoxide (CO) is introduced. Formylpyrrolidine (FPyr) and trichlorotriazine (TCT), which is a cost‐efficient commodity chemical, enable this decarbonylation. Utilization of dimethylformamide (DMF) as solvent and catalyst even allows for a rapid CO generation at room temperature. Application towards four different carbonylative cross coupling protocols demonstrates the high synthetic utility and versatility of the new approach. Remarkably, this also comprehends a carbonylative Sonogashira reaction at room temperature employing intrinsically difficult electron‐deficient aryl iodides. Commercial ¹³C‐enriched formic acid facilitates the production of radiolabeled compounds as exemplified by the pharmaceutical Moclobemide. Finally, comparative experiments verified that the present method is highly superior to other protocols for the activation of carboxylic acids.

Formamide catalyzed activation of carboxylic acids - versatile and cost-efficient amidation and esterification

Formamide catalysis enables highly cost-efficient amide C–N and ester C–O bond formation through carboxylic acid chlorides as essential intermediates.

A novel, broadly applicable method for amide C–N and ester C–O bond formation is presented based on formylpyrrolidine (FPyr) as a Lewis base catalyst. Herein, trichlorotriazine (TCT), which is the most cost-efficient reagent for OH-group activation, was employed in amounts of ≤40 mol% with respect to the starting material (100 mol%). The new approach is distinguished by excellent cost-efficiency, waste-balance (E-factor down to 3) and scalability (up to >80 g). Moreover, high levels of functional group compatibility, which includes acid-labile acetals and silyl ethers, are demonstrated and even peptide C–N bonds can be formed. In comparison to reported amidation procedures using TCT, yields are considerably improved (for instance from 26 to 91%) and esterification is facilitated for the first time in synthetically useful yields. These significant enhancements are rationalized by activation by means of acid chlorides instead of less electrophilic acid anhydride intermediates.

A General Catalytic Method for Highly Cost- and Atom-Efficient Nucleophilic Substitutions

A general formamide-catalyzed protocol for the efficient transformation of alcohols into alkyl chlorides, which is promoted by substoichiometric amounts (down to 34 mol %) of inexpensive trichlorotriazine (TCT), is introduced. This is the first example of a TCT-mediated dihydroxychlorination of an OH-containing substrate (e.g., alcohols and carboxylic acids) in which all three chlorine atoms of TCT are transferred to the starting material. The consequently enhanced atom economy facilitates a significantly improved waste balance (E-factors down to 4), cost efficiency, and scalability (>50 g). Furthermore, the current procedure is distinguished by high levels of functional-group compatibility and stereoselectivity, as only weakly acidic cyanuric acid is released as exclusive byproduct. Finally, a one-pot protocol for the preparation of amines, azides, ethers, and sulfides enabled the synthesis of the drug rivastigmine with twofold S_N 2 inversion, which demonstrates the high practical value of the presented method.

Scale-Up Synthesis and Identification of GLYX-13, a NMDAR Glycine-Site Partial Agonist for the Treatment of Major Depressive Disorder

GLYX-13, a NMDAR glycine-site partial agonist, was discovered as a promising antidepressant with rapidly acting effects but no ketamine-like side effects. However, the reported synthetic process route had deficiencies of low yield and the use of unfriendly reagents. Here, we report a scaled-up synthesis of GLYX-13 with an overall yield of 30% on the hectogram scale with a column chromatography-free strategy, where the coupling and deprotection reaction conditions were systematically optimized. Meanwhile, the absolute configuration of precursor compound of GLYX-13 was identified by X-ray single crystal diffraction. Finally, the activity of GLYX-13 was verified in the cortical neurons of mice through whole-cell voltage-clamp technique.

An efficient mechanochemical synthesis of amides and dipeptides using 2,4,6-trichloro-1,3,5-triazine and PPh3

A mechanochemical method for amidation of carboxylic acids and urethane-protected (Fmoc, Cbz, Boc) α-amino acids has been developed as a facile, efficient, and eco-friendly route toward amides and dipeptides.

Synthesis and conformational studies of a stable peptidomimetic β-hairpin based on a bifunctional diketopiperazine turn inducer

A new β-hairpin mimic foldamer based on the assembly of a reverse turn inducer, a peptidomimetic strand, and a tetrapeptide sequence was prepared, and its conformation in solution was assessed by NMR and computational investigations.

A hyaluronic acid–pentamidine bioconjugate as a macrophage mediated drug targeting delivery system for the treatment of leishmaniasis

A new HA–Pent bioconjugate was synthetized and proposed as drug targeting delivery system for the treatment of leishmaniasis, exploiting the specific biological recognition of HA by the macrophage.

Solvent-free reduction of carboxylic acids to alcohols with NaBH4promoted by 2,4,6-trichloro-1,3,5-triazine and PPh3in the presence of K2CO3

The first simple, rapid, and eco-friendly method for NaBH₄reduction of carboxylic acids to alcohols under solvent-free conditions is reported.

Cyanuric chloride catalyzed mild protocol for synthesis of biologically active dihydro/spiro quinazolinones and quinazolinone-glycoconjugates

We have developed an efficient cyanuric chloride (2,4,6-trichloro-1,3,5-triazine, TCT) catalyzed approach for the synthesis of 2,3-dihydroquinazolin-4(1H)-one (3a-3x), 2-spiroquinazolinone (5, 7), and glycoconjugates of 2,3-dihydroquinazolin-4(1H)-one (10a, 10b) derivatives. The reaction allows rapid cyclization (8-20 min) with 10 mol % cyanuric chloride to give skeletal complexity in good to excellent yield. We believe that this novel procedure may open the door for the easy generation of new and bioactive quinazolinones.

Hyaluronic acid derivatives prepared in aqueous media by triazine-activated amidation

A method is presented for the preparation of hyaluronic acid derivatives obtained through triazine-activated amidation. A number of amines were successfully reacted with hyaluronic acid carboxyl groups using 2-chloro-4,6-dimethoxy-1,3,5-triazine as an activating species in a mixture of water and acetonitrile under neutral conditions. By varying the amount of triazine reagent, it was possible to control the degree of modification. Depending on the amine chosen, degrees of modification ranging from 3 to 20% were obtained when using 0.5 equiv of the triazine to hyaluronic acid carboxyl groups. The possibility to perform the reaction in a mixture of water and acetonitrile facilitates the introduction of a wide range of both hydrophilic and hydrophobic amines. Triazine-activated amidation appears to be a highly versatile, controllable, and relatively mild technique for modification of hyaluronic acid, and we predict that it will be useful in the design of novel hyaluronic acid based biomaterials.

N-Triazinylammonium Tetrafluoroborates. A New Generation of Efficient Coupling Reagents Useful for Peptide Synthesis

A new generation of triazine-based coupling reagents (TBCRs), designed according to the concept of "superactive esters", was obtained by treatment of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium (DMTMM) chloride with lithium or silver tetrafluoroborate. The structure of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium tetrafluoroborate was confirmed by X-ray diffraction. Activation of carboxylic acids by using this reagent proceeds via triazine "superactive ester". The coupling reagent was successfully used for the synthesis of Z-, Boc-, and Fmoc-protected dipeptides derived from natural and unnatural sterically hindered amino acids and for fragment condensation, in 80-100% yield and with high enantiomeric purity. The manual SPPS of the ACP(65-74) peptide fragment (H-Val-Gln-Ala-Ala-Ile-Asp-Tyr-Ile-Asn-Gly-OH) proceeded significantly faster than with TBTU or HATU, as well as the automated SPPS of the same fragment gave a purer product than by using TBTU or PyBOP. The reagent was also demonstrated to be efficient in on-resin head-to-tail cyclization of constrained cyclopeptides, in SPPS synthesis of Aib peptides, and in the synthesis of esters from appropriate acids, alcohols, and phenols. The high efficiency and versatility of this new generation of TBCRs confirm, for the first time, the usefulness of the concept of "superactive esters" in rational design of the structure of coupling reagents.

Anchor-based design of improved cholera toxin and E. coli heat-labile enterotoxin receptor binding antagonists that display multiple binding modes

The action of cholera toxin and E. coli heat-labile enterotoxin can be inhibited by blocking their binding to the cell-surface receptor GM1. We have used anchor-based design to create 15 receptor binding inhibitors that contain the previously characterized inhibitor MNPG as a substructure. In ELISA assays, all 15 compounds exhibited increased potency relative to MNPG. Binding affinities for two compounds, each containing a morpholine ring linked to MNPG via a hydrophobic tail, were characterized by pulsed ultrafiltration (PUF) and isothermal titration calorimetry (ITC). Crystal structures for these compounds bound to toxin B pentamer revealed a conserved binding mode for the MNPG moiety, with multiple binding modes adopted by the attached morpholine derivatives. The observed binding interactions can be exploited in the design of improved toxin binding inhibitors.

Triazine-based condensing reagents

The synthesis, properties, and application of condensing reagents derived from 1,3,5-triazines are described. The mechanism of activation of carboxylic function, structure of reactive intermediates, and mechanism of acylation of nucleophiles are presented. The synthetic versatility of mono- and bifunctional reagents for syntheses in solution, triazine-based immobilized reagents, chiral triazines for enantiodifferentiating syntheses, are discussed. The scope and limitation of the synthetic utility of triazine reagents in the preparation of heterocyclic compounds, amides, esters, oligopeptides-including large-scale syntheses and use in the combinatorial chemistry-is demonstrated.