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The Prelude of Green Syntheses of Drugs and Natural Products
Published in Ahindra Nag, Greener Synthesis of Organic Compounds, Drugs and Natural Products, 2022
Leonardo Xochicale-Santana, C. C. Vidyasagar, Blanca M. Muñoz-Flores, Víctor M. Jiménez Pérez
Mechanosynthesis is a technique based on solid-state reactions, using grinding as a process. An advantage of this technique is to avoid the excessive use of solvents to carry out a successful chemical reaction. The development of this technique as a synthetic method has been excellently supported by obtaining results over the last few years in a wide variety of applications,6 as a method for obtaining leading drug structures. For example, Colacino and co-workers prepared disubstituted hydantoins using an eco-friendly methodology,7 applying the mechanosynthesis technique as an easy-handling tool. Hydantoins are a group found in a wide variety of drugs, hydantoin derivatives are used as anticonvulsants,8 muscle relaxants, antidiabetics,9 antiandrogenic, or antifungal activities.10 The application of this tool entails obtaining the disubstituted hydantoins in excellent yields from amino ester hydrochloride (1), in addition to avoiding the use of toxic substances to prepare said structures.11 This methodology was applied to the “green synthesis” of the antiepileptic drug Phenytoin (Scheme 15.1).
N-Polyheterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
2-(Arylamino)benzimidazoles are synthesized by cyclocondensation of poly(ethylene glycol)-supported o-phenylenediamines with isothiocyanates under microwaves, followed by separation of the product from the polymer support [142]. For considerable cyclization, either reflux in methanol for 4 hours or microwave heating for 10 minutes are required (Scheme 65). The isolation of products can be simplified substantially through a soluble poly(ethylene glycol) matrix as poly(ethylene glycol)-bound products can be precipitated selectively from a suitable combination of solvents. Similarly, MeO-poly(ethylene glycol)-OH can be removed from the homogeneous solution by precipitation and filtration after microwave-assisted cleavage of the substituted benzimidazoles from the polymer support. All polymer-supported intermediates and the polymer support itself remain stable under microwaves. It is easy to monitor soluble polymer-supported reactions by conventional analytical methods, unlike the solid-phase synthesis. Later on, Lin and Sun [143] reported that the conversion of diamine into benzimidazoles (through the formation of N,N-disubstituted thiourea intermediate) under microwaves is facilitated by bismuth chloride and mercury(II) chloride [144] as catalysts. Microwave-assisted combinatorial synthesis of libraries of hydantoins [145–146] and thiohydantoins [147] in soluble poly(ethylene glycol)-matrix has also been studied by researchers. Another method involves a parallel preparation of 1,5-disubstituted thiohydantoins and hydantoins [148] in the presence of polyphosphoric ester under solvent-free conditions. Furthermore, an entire class of 3,5,5-trisubstituted hydantoins can be produced by the condensation of substituted benzils with ureas under microwaves, followed by N3-alkylation [72b, 149].
Pyrimidine derivative-based cyanide-free silver electroplating bath
Published in Transactions of the IMF, 2022
Atiqah Binti Jasni, Sachio Yoshihara, Fumio Aiki, Hideki Watanabe
In this study, the authors examine the use of hydantoin and pyrimidine derivative as a silver complexing agent to develop a cyanide-free silver electroplating process for the electronics manufacturing industry. Hydantoin is a heterocyclic organic compound with the formula CH2C(O)NHC(O)NH, while pyrimidine is a six-membered heterocyclic with two nitrogen atoms in which the nitrogen atoms are at positions 1 and 3 in the ring. Here, two types of pyrimidine derivatives, 2,4-pyrimidinedione (Uracil) and 5-methyluracil (Thymine), and one type of hydantoin derivative, 5,5-dimethylhydantoin (DMH), were selected as complexing agents. The influence of combining two types of complexing agents in the silver plating solution and on its deposit was studied.
Bioprocessing of recombinant proteins from Escherichia coli inclusion bodies: insights from structure-function relationship for novel applications
Published in Preparative Biochemistry & Biotechnology, 2023
Kajal Kachhawaha, Santanu Singh, Khyati Joshi, Priyanka Nain, Sumit K. Singh
Table 3 lists the commonly used methods of protein refolding and their associated advantages/disadvantages. As evident from the table, each refolding condition must be optimized on a case-to-case basis depending on the propensity of the IB to aggregate and the scale of the operation. For example, while dilution of denaturants or chromatography-based processes is an attractive option for protein refolding at a laboratory scale, the large volume of buffer used necessitates an additional concentration step, which adds to the cost and time of bioprocessing. Likewise, refolding proteins at an industrial scale should also yield a high concentration of refolded protein output. A dialysis-based method is suitable for obtaining a high concentration of the refolded protein output.[127] However, the rate-limiting step of removing denaturants from the membrane makes dialysis-based refolding exceedingly time-consuming.[7] This step could be hastened by increasing the membrane surface area (i.e., membrane area per volume of denatured protein solution). Kato et al. achieved this objective by employing a chemical engineering approach wherein they incorporated a dialysis membrane into a microchannel. They successfully refolded a model protein (known to be difficult to refold) with an eight-fold concentration instead of the dilution-based method in under 20 min using this custom-designed dialysis setup.[128,129] However, the size of such refolding apparatus limits the volume of solubilized IB that could be handled. Also, rapid mixing of the solubilized IB and refolding buffer in the microchannel may result in protein aggregation. The use of aggregation suppressors such as arginine, allantoin, and hydantoin could prevent aggregate formation in such instances.[130]