Expeditious synthesis of 2,3-dihydroquinazolin-4(1H)-ones in aqueous medium using thiamine hydrochloride (VB1) as a mild, efficient, and reusable organocatalyst

Thiamine (Vitamin B1) Promoted Organic Transformations: A Recent Updates

Due to the growing significance of sustainable and environmentally friendly organic transformations, there has been increasing interest in utilizing vitamins as catalysts owing to their green nature, biocompatibility, and ease of preparation. Among these, Vitamin B1, also known as thiamine stands out for its nonflammable, water-soluble, inexpensive, and non-toxic characteristics. This review summarized recent developments on the catalytic application of Vitamin B1 in organic transformations, particularly in facilitating C-C and C-X (N, O, S) bond formations, thus demonstrating its efficacy in synthesizing complex molecules. Vitamin B1 exhibits versatility in these reactions, functioning as both an organocatalyst as well as a co-catalyst or ligand with other metal catalysts. The review also delves into the application of thiamine diphosphate-dependent enzymes as catalysts in organic reactions, drawing inspiration from natural enzymatic processes. Additionally, the mechanistic intricacies of thiamine-catalyzed reactions and the roles of co-catalysts or additives are thoroughly examined, providing insights into reaction pathways and facilitating informed catalyst design strategies.

Wang resin catalysed sonochemical synthesis of pyrazolo[4,3-d]pyrimidinones and 2,3-dihydroquinazolin-4(1H)-ones: Identification of chorismate mutase inhibitors having effects on Mycobacterium tuberculosis cell viability

The enzyme chorismate mutase (or CM that is vital for the survival of bacteria) is an interesting pharmacological target for the identification of new anti-tubercular agents. The 5,5-disibstituted pyrazolo[4,3-d]pyrimidinone derivatives containing the fragment based on 4-amino-1-methyl-3-propyl-1H-pyrazole-5-carboxamide were designed and explored as the potential inhibitors of chorismate mutase. Based on encouraging docking results of two representative molecules evaluated in silico against MtbCM (PDB: 2FP2) the Wang resin catalysed sonochemical synthesis of target N-heteroarenes were undertaken. The methodology involved the reaction of 4-amino-1-methyl-3-propyl-1H-pyrazole-5-carboxamide with the appropriate cyclic/acyclic ketones to afford the desired products in acceptable (51-94%) yields. The methodology was also extended successfully towards the synthesis of 2,2-disubstituted 2,3-dihydroquinazolin-4(1H)-ones in excellent (85-90%) yields. In vitro MTT assay against the RAW 264.7 cell line followed by enzymatic assay against MtbCM identified 3b and 3c as active compounds that showed two H-bonding via their NH (at position 6) and CO group with MtbCM in silico and encouraging (54-57%) inhibition at 30 µM in vitro. Notably, none of the 2,2-disubstituted 2,3-dihydroquinazolin-4(1H)-ones showed any significant inhibition of MtbCM suggesting the favourable role of the pyrazole moiety in case of pyrazolo[4,3-d]pyrimidinones. The favourable role of cyclopentyl ring attached to the pyrazolo[4,3-d]pyrimidinone moiety and that of two methyl groups in place of cyclopentyl ring was also indicated by the SAR study. Besides showing effects against MtbCM in the concentration response study, 3b and 3c showed little or no effects on mammalian cell viability up to 100 µM in an MTT assay but decreased the % Mtb cell viability at 10-30 µM with > 20% decrease at 30 µM in an Alamar Blue Assay. Moreover, no adverse effects were noted for these compounds when tested for teratogenicity and hepatotoxicity in zebrafish at various concentrations. Overall, being the only example of MtbCM inhibitors that showed effects on Mtb cell viability the compound 3b and 3c are of further interest form the view point of discovery and development of new anti-tubercular agents.

Recent advances and prospects in the organocatalytic synthesis of quinazolinones

Quinazolinone, a bicyclic compound, comprises a pyrimidine ring fused at 4´ and 8´ positions with a benzene ring and constitutes a substantial class of nitrogen-containing heterocyclic compounds on account of their frequent existence in the key fragments of many natural alkaloids and pharmaceutically active components. Consequently, tremendous efforts have been subjected to the elegant construction of these compounds and have recently received immense interest in synthetic and medicinal chemistry. The domain of synthetic organic chemistry has grown significantly over the past few decades for the construction of highly functionalized therapeutically potential complex molecular structures with the aid of small organic molecules by replacing transition-metal catalysis. The rapid access to this heterocycle by means of organocatalytic strategy has provided new alternatives from the viewpoint of synthetic and green chemistry. In this review article, we have demonstrated a clear presentation of the recent organocatalytic synthesis of quinazolinones of potential therapeutic interests and covered the literature from 2015 to date. In addition to these, a clear presentation and understanding of the mechanistic aspects, features, and limitations of the developed reaction methodologies have been highlighted.

Organocatalyzed Heterocyclic Transformations In Green Media: A Review

Background:

Since the discovery of metal-free catalysts or organocatalysts about twenty years ago, a number of small molecules with different structures have been used to accelerate organic transformations. With the development of environmental awareness, to obtain highly efficient scaffolds, scientists have directed their studies towards synthetic methodologies that minimize or preferably eliminate the formation of waste, avoid toxic solvents and reagents and use renewable starting materials as far as possible.

Methods:

In this connection, the organocatalytic reactions providing efficiency and selectivity for most of the transformations have become an endless topic in organic chemistry since several advantages from both practical and environmental standpoints. Organocatalysts contributing to the transformation of reactants into products with the least possible waste production, have been serving the concept of green chemistry.

Results and Conclusion:

Organocatalysts have been classified based on their binding capacity to the substrate with covalent or noncovalent interactions involving hydrogen bonding and electrostatic interaction. Diverse types of small organic compounds including proline and its derivatives, phase-transfer catalysts, (thio)urease, phosphoric acids, sulfones, N-oxides, guanidines, cinchona derivatives, aminoindanol, and amino acids have been utilized as hydrogen bonding organocatalysts in different chemical transformations.

Photocatalyst-free visible-light-promoted quinazolinone synthesis at room temperature utilizing aldehydes generated in situ via C[double bond, length as m-dash]C bond cleavage

This is the first report on a facile tandem route for synthesizing quinazolinones at room temperature from various aminobenzamides and in situ-generated aldehydes. The latter was formed via C[double bond, length as m-dash]C bond cleavage, and the overall reaction proceeded using molecular oxygen as a clean oxidant in the absence of a photocatalyst. Visible light, which was indispensable for the entire course of the reaction, played multiple roles. It initially cleaved styrene to an aldehyde, then facilitated its cyclization with an o-substituted aniline, and finally promoted the dehydrogenation of the cyclized intermediate. The previous step provided the feedstock for the next step in the reaction, thereby preventing volatilization, oxidation, and polymerization of the aldehyde. Thus, the overall process is simple, environmentally benign, and economically feasible.

An Aqueous Facile Synthesis of 2,3-Dihydroquinazolin-4(1H)-One Derivatives by Reverse Zinc Oxide Micelles as Nanoreactor

A green synthetic protocol has been developed for the efficient preparation of 2,3-dihydroquinazolin−4(1H)-one derivatives with excellent yield in aqueous media. Reverse zinc oxide micelles catalyzed the reactions efficiently and selectively as the hallow nanoreactor. Moreover, the catalyst was reusable without significant loss of catalytic efficiency. The notable advantages of the procedure are high yields and mild reaction conditions, simple operation, nonchromatographic purification, environmentally friendly and good versatile substrates.