D-Glucosamine in iron-catalysed cross-coupling reactions of Grignards with allylic and vinylic bromides: application to the synthesis of a key sitagliptin precursor

Green Chemistry in the Synthesis of Pharmaceuticals

The principles of green chemistry (GC) can be comprehensively implemented in green synthesis of pharmaceuticals by choosing no solvents or green solvents (preferably water), alternative reaction media, and consideration of one-pot synthesis, multicomponent reactions (MCRs), continuous processing, and process intensification approaches for atom economy and final waste reduction. The GC's execution in green synthesis can be performed using a holistic design of the active pharmaceutical ingredient's (API) life cycle, minimizing hazards and pollution, and capitalizing the resource efficiency in the synthesis technique. Thus, the presented review accounts for the comprehensive exploration of GC's principles and metrics, an appropriate implication of those ideas in each step of the reaction schemes, from raw material to an intermediate to the final product's synthesis, and the final execution of the synthesis into scalable industry-based production. For real-life examples, we have discussed the synthesis of a series of established generic pharmaceuticals, starting with the raw materials, and the intermediates of the corresponding pharmaceuticals. Researchers and industries have thoughtfully instigated a green synthesis process to control the atom economy and waste reduction to protect the environment. We have extensively discussed significant reactions relevant for green synthesis, one-pot cascade synthesis, MCRs, continuous processing, and process intensification, which may contribute to the future of green and sustainable synthesis of APIs.

Efficient and Straightforward Syntheses of Two United States Pharmacopeia Sitagliptin Impurities: 3-Desamino-2,3-dehydrositagliptin and 3-Desamino-3,4-dehydrositagliptin

Various organic impurities (starting materials, reagents, intermediates, degradation products, by-products, and side products) could be present in active pharmaceutical ingredients affecting their qualities, safeties, and efficacies. Herein, we present the efficient syntheses of two United States Pharmacopeia impurities of an antidiabetic drug sitagliptin, a potent and orally active dipeptidyl peptidase IV inhibitor: 3-desamino-2,3-dehydrositagliptin and 3-desamino-3,4-dehydrositagliptin. Our three-step synthetic approach is based on the efficient cobalt-catalyzed cross-coupling reaction of 1-bromo-2,4,5-trifluorobenzene and methyl 4-bromocrotonate in the first step, followed by hydrolysis of corresponding ester with 3 M HCl to (E)-(2,4,5-trifluorophenyl)but-2-enoic acid in high overall yield, whereas the reaction with 3 M NaOH resulted in the carbon-carbon double bond regio-isomerization and hydrolysis to give the (E)-(2,4,5-trifluorophenyl)but-3-enoic acid in 92% yield. Both acid derivatives were converted to title compounds via the amide bond formation with 3-(trifluoromethyl)-5,6,7,8-tetrahydro-[1,2,4]triazolo[4,3-a]pyrazine. Extensive screening of coupling/activation reagents, bases, and solvents reviled that the amide bond is formed the most efficiently using the (COCl)2/Et3N in THF or alternatively EDC/NMM/(DMAP or HOBt) in DMF obtaining the title compounds in 68-76% yields and providing the overall yields for the three-step process in the range of 57-64% on a gram scale. The presented study also demonstrates the importance of a proper selection of solvent, base, and coupling/activating reagent for amide bond formation using Michael acceptor-type allylbenzene derivatives as coupling partners to minimize the carbon-carbon double bond regio-isomerization.

Iron-Catalyzed Cross-Couplings in the Synthesis of Pharmaceuticals: In Pursuit of Sustainability

The scarcity of precious metals has led to the development of sustainable strategies for metal-catalyzed cross-coupling reactions. The establishment of new catalytic methods using iron is attractive owing to the low cost, abundance, ready availability, and very low toxicity of iron. In the last few years, sustainable methods for iron-catalyzed cross-couplings have entered the critical area of pharmaceutical research. Most notably, iron is one of the very few metals that have been successfully field-tested as highly effective base-metal catalysts in practical, kilogram-scale industrial cross-couplings. In this Minireview, we critically discuss the strategic benefits of using iron catalysts as green and sustainable alternatives to precious metals in cross-coupling applications for the synthesis of pharmaceuticals. The Minireview provides an essential introduction to the fundamental aspects of practical iron catalysis, highlights areas for improvement, and identifies new fields to be explored.

Recent advances in iron-catalysed cross coupling reactions and their mechanistic underpinning

Advances in iron-catalysed cross coupling from 2010–2015 are critically reviewed.