Microwave assisted one-pot catalyst free green synthesis of new methyl-7-amino-4-oxo-5-phenyl-2-thioxo-2,3,4,5-tetrahydro-1H-pyrano[2,3-d]pyrimidine-6-carboxylates as potent in vitro antibacterial and antifungal activity

From Batch to the Semi-Continuous Flow Hydrogenation of pNB, pNZ-Protected Meropenem

Meropenem is currently the most common carbapenem in clinical applications. Industrially, the final synthetic step is characterized by a heterogeneous catalytic hydrogenation in batch mode with hydrogen and Pd/C. The required high-quality standard is very difficult to meet and specific conditions are required to remove both protecting groups [i.e., p-nitrobenzyl (pNB) and p-nitrobenzyloxycarbonyl (pNZ)] simultaneously. The three-phase gas-liquid-solid system makes this step difficult and unsafe. The introduction of new technologies for small-molecule synthesis in recent years has opened up new landscapes in process chemistry. In this context, we have investigated meropenem hydrogenolysis using microwave (MW)-assisted flow chemistry for use as a new technology with industrial prospects. The reaction parameters (catalyst amount, T, P, residence time, flow rate) in the move from the batch process to semi-continuous flow were investigated under mild conditions to determine their influence on the reaction rate. The optimization of the residence time (840 s) and the number of cycles (4) allowed us to develop a novel protocol that halves the reaction time compared to batch production (14 min vs. 30 min) while maintaining the same product quality. The increase in productivity using this semi-continuous flow technique compensates for the slightly lower yield (70% vs. 74%) obtained in batch mode.

Microwave Induced Green Synthesis: Sustainable Technology for Efficient Development of Bioactive Pyrimidine Scaffolds

Microwave radiation is used as a heating source during the synthesis of heterocyclic compounds. The heating mechanisms involved in microwave-induced synthesis include dipolar polarization and ionic conduction. This heating technology follows the green protocol as it involves the use of recyclable organic solvents during synthesis. The microwave heating approach offers a faster rate of reaction, easier work-up procedure, and higher product yield with purity and also reduces environmental pollution. So, microwave heating is applied as a sustainable technology for the efficient production of pyrimidine compounds as one of the heterocyclic moieties. Pyrimidine is a six-membered nitrogenous heterocyclic compound that plays a significant role due to several therapeutic applications. This moiety acts as an essential building block for generating drug candidates with diverse biological activities, including anti-cancer (capecitabine), anti-thyroid (propylthiouracil), antihistaminic (pemirolast), antimalarial (pyrimethamine), antidiabetic (alloxan), antihypertensive (minoxidil), anti-inflammatory (octotiamine), antifungal (cyprodinil), antibacterial (sulfamethazine), etc. This review is focused on the synthesis of pyrimidine analogs under microwave irradiation technique and the study of their therapeutic potentials.

Insights into the recent progress in the medicinal chemistry of pyranopyrimidine analogs

Heterocycles containing the pyranopyrimidine motif have attracted the interest of researchers in recent decades due to their ability to synthesize and explore at a large scale to explore the biological diversity. Therefore, this review highlights the biological characteristics and synthetic approaches adopted to prepare pyranopyrimidine analogs in the last five years. Several novel preparation procedures have been summarized to synthesize these compounds using ionic, basic, or nanocatalysts or catalyst-free conditions to obtain these compounds in good yields. Pyranopyrimidines could also be used as ligands in the preparation of metal complexes with increased biological potency. The different sections include the antimicrobial, antitubercular, antimalarial, antiviral "SARS-CoV-2 inhibitors", antidiabetic, antitumor, cytotoxic, antiinflammatory, antioxidant, anticoagulant, urease inhibitory activities, and tyrosine inhibitors. The results are discussed based on the structure-activity relationships (SARs) and the mechanism of action.

Synthesis and in vitro evaluation of antitumor activity of spiro[indolo[2,1-b]quinazoline-pyrano[2,3-d]pyrimidine] and spiro[indolo[2,1-b]quinazoline-pyrido[2,3-d]pyrimidine] derivatives by using 2D and 3D cell culture models

Cancer as one of the biggest human health problems remains unsolved. The identification of novel platforms with the highest efficacy and low toxicity is a big challenge among interested researchers. In this regard, we are interested to synthesis and evaluate antitumor activity of spiro[indolo[2,1-b]quinazoline-pyrano[2,3-d]pyrimidine] and spiro[indolo[2,1-b]quinazoline-pyrido[2,3-d]pyrimidine] derivatives. The spiro heterocycles were synthesized via four-component reaction of isatoic anhydride, isatins, malononitrile, and some CH-acids including barbituric acid/thiobarbituric acid and 4(6)-aminouracil in CH₂Cl₂ under reflux condition. The significant features of this process are short reaction time, easy purification without chromatographic process, and high yields which make it attractive. Next, we employed 2D and 3D cell culture models to evaluate biological activity of our compounds. Our results showed that among our seven products (4a-g), the compounds 4a and 4e are the best with 50% growth inhibitory concentration (IC₅₀) value lower than etoposide. Our results support this idea that the compounds 4a and 4e may be potential for drug designing in cancer therapy. However, more experiments will be required to find possible side effects of related compounds in vivo.

Recent advancements in the multicomponent synthesis of heterocycles integrated with a pyrano[2,3-d]pyrimidine core

Heterocyclic compounds incorporated with a pyranopyrimidine skeleton have received substantial consideration owing to their privileged, and intelligible biodiversity. Accordingly, this review highlights the multicomponent synthetic routes adopted to prepare heterocyclic compounds incorporated with the pyrano[2,3-d]pyrimidine skeleton in the preceding two years. The different sections comprise the synthesis of bicyclic, tricyclic, polycyclic, and spirocyclic systems along with the estimation of the probable mechanistic routes for the reaction pathways. Commonly, the pyran ring closure was the major idea of most studies, and the mechanistic pathways of these reactions involved Knoevenagel condensation, Michael addition, and intramolecular cyclocondensation. Besides, the significant biological potency of the compounds recently synthesized from multicomponent reactions is deliberated.

The present review highlighted the recent developments of the multicomponent synthesis of heterocyclic compounds with pyrano[2,3-d]pyrimidine skeleton applying the diverse strategies.

Microwave Domino Diastereoselective Synthesis of Novel Trans-4,5-Dihydro-1H-Furo[2,3-c]Pyrazoles Using Pyridinium Salts in an Aqueous Medium

Novel fused 4,5-dihydro-1 H-furo[2,3- c]pyrazole derivatives containing both biologically active pyrazole and furan templates are synthesised by a one-pot two-step four-component domino reaction involving hydrazine hydrate, a β-keto ester, an aromatic aldehyde and a pyridinium salt catalysed by DABCO with high diastereoselectivity in H2O under microwave irradiation. To minimise the formation of byproducts, the hydrazine hydrate and ethyl acetoacetate were first irradiated until a pyrazolone was formed. Next, the aryl aldehyde, the pyridinium salt and DABCO were added and the reaction could be completed in good to excellent yields. The salient features of this eco-friendly methodology are highlighted by its short reaction time (10–12 min), high yields, high atom-economy, efficiency of producing five new bonds (2C–C, C=N, C–N and one C–O), two new rings and two stereocentres in a single operation, absence of any tedious work-up or purification and avoidance of separation of intermediates.

Synthesis and antimicrobial activity of new piperazine-based heterocyclic compounds

The hydrazide