A Novel Method for Large-Scale Synthesis of Lamivudine through Cocrystal Formation of Racemic Lamivudine with (S)-(−)-1,1′-Bi(2-naphthol) [(S)-(BINOL)]

Advances and applications of chiral resolution in pharmaceutical field

The attention to chiral drugs has been raised to an unprecedented level as drug discovery and development strategies grow rapidly. However, separation of enantiomers is still a huge task, which leads to an increasing significance to equip a wider range of expertise in chiral separation science to meet the current and future challenges. In the last few decades, remarkable progress of chiral resolution has been achieved. This review summarizes and classifies chiral resolution methods in analytical scale and preparative scale systematically and comprehensively, including crystallization-based method, inclusion complexation, chromatographic separation, capillary electrophoresis, kinetic resolution, liquid-liquid extraction, membrane-based separation, and especially one bold new progress based on chiral-induced spin selectivity theory. The advances and recent applications will be presented in detail, in which the contents may bring more thinking to wide-ranging readers in various professional fields, from analytical chemistry, pharmaceutical chemistry, natural medicinal chemistry, to manufacturing of drug production.

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

Sugar-modified nucleosides have gained considerable attention in the scientific community, either for use as molecular probes or as therapeutic agents. When the methylene group of the ribose ring is replaced with a sulfur atom at the 3’-position, these compounds have proved to be structurally potent nucleoside analogues, and the best example is BCH-189. The majority of methods traditionally involves the chemical modification of nucleoside structures. It requires the creation of artificial sugars, which is accompanied by coupling nucleobases via N-glycosylation. However, over the last three decades, efforts were made for the synthesis of 1,3-oxathiolane nucleosides by selective N-glycosylation of carbohydrate precursors at C-1, and this approach has emerged as a strong alternative that allows simple modification. This review aims to provide a comprehensive overview on the reported methods in the literature to access 1,3-oxathiolane nucleosides. The first focus of this review is the construction of the 1,3-oxathiolane ring from different starting materials. The second focus involves the coupling of the 1,3-oxathiolane ring with different nucleobases in a way that only one isomer is produced in a stereoselective manner via N-glycosylation. An emphasis has been placed on the C–N-glycosidic bond constructed during the formation of the nucleoside analogue. The third focus is on the separation of enantiomers of 1,3-oxathiolane nucleosides via resolution methods. The chemical as well as enzymatic procedures are reviewed and segregated in this review for effective synthesis of 1,3-oxathiolane nucleoside analogues.

Enantioselective synthesis of ammonium cations

Control of molecular chirality is a fundamental challenge in organic synthesis. Whereas methods to construct carbon stereocentres enantioselectively are well established, routes to synthesize enriched heteroatomic stereocentres have garnered less attention^1-5. Of those atoms commonly present in organic molecules, nitrogen is the most difficult to control stereochemically. Although a limited number of resolution processes have been demonstrated^6-8, no general methodology exists to enantioselectively prepare a nitrogen stereocentre. Here we show that control of the chirality of ammonium cations is easily achieved through a supramolecular recognition process. By combining enantioselective ammonium recognition mediated by 1,1'-bi-2-naphthol scaffolds with conditions that allow the nitrogen stereocentre to racemize, chiral ammonium cations can be produced in excellent yields and selectivities. Mechanistic investigations demonstrate that, through a combination of solution and solid-phase recognition, a thermodynamically driven adductive crystallization process is responsible for the observed selectivity. Distinct from processes based on dynamic and kinetic resolution, which are under kinetic control, this allows for increased selectivity over time by a self-corrective process. The importance of nitrogen stereocentres can be revealed through a stereoselective supramolecular recognition, which is not possible with naturally occurring pseudoenantiomeric Cinchona alkaloids. With practical access to the enantiomeric forms of ammonium cations, this previously ignored stereocentre is now available to be explored.

An industrial perspective on co-crystals: Screening, identification and development of the less utilised solid form in drug discovery and development

Active pharmaceutical ingredients are commonly marketed as a solid form due to ease of transport, storage and administration. In the design of a drug formulation, the selection of the solid form is incredibly important and is traditionally based on what polymorphs, hydrates or salts are available for that compound. Co-crystals, another potential solid form available, are currently not as readily considered as a viable solid form for the development process. Even though co-crystals are gaining an ever-increasing level of interest within the pharmaceutical community, their acceptance and application is still not as standard as other solid forms such as the ubiquitous pharmaceutical salt and stabilised amorphous formulations. Presented in this chapter is information that would allow for a co-crystal screen to be planned and conducted as well as scaled up using solution and mechanochemistry based methods commonly employed in both the literature and industry. Also presented are methods for identifying the formation of a co-crystal using a variety of analytical techniques as well as the importance of confirming the formation of co-crystals from a legal perspective and demonstrating the legal precedent by looking at co-crystalline products already on the market. The benefits of co-crystals have been well established, and presented in this chapter are a selection of examples which best exemplify their potential. The goal of this chapter is to increase the understanding of co-crystals and how they may be successfully exploited in early stage development.

A review on Arthrobacter sp. lipase: A versatile biocatalyst for the kinetic resolution to access enantiomerically pure/enriched compounds

Over the last few years, there has been a dramatic increase in the number of reports related to Arthrobacter sp. lipase (ABL:MTCC No. 5125) catalyzed kinetic resolution performed in biphasic media. A strain displaying esterase/lipase activity and designated as ABL was isolated, during the course of a screening program at Indian Institute of Integrative Medicine, Jammu. Considerable research has shown that reactions catalyzed by ABL are more selective than many commercial lipases. Since new applications of this lipase are emerging, there is a great need to provide all the relevant information exclusively. This review article is an attempt to cover all the relevant reports based on isolation, purification, immobilization, and application of ABL in the biopharmaceutical sector.

Synthesis of an Oxathiolane Drug Substance Intermediate Guided by Constraint-Driven Innovation

A new route was developed for construction of the oxathiolane intermediate used in the synthesis of lamivudine (3TC) and emtricitabine (FTC). We developed the presented route by constraining ourselves to low-cost, widely available starting materials—we refer to this as supply-centered synthesis. Sulfenyl chloride chemistry was used to construct the framework for the oxathiolane from acyclic precursors. This bond construction choice enabled the use of chloroacetic acid, vinyl acetate, sodium thiosulfate, and water to produce the oxathiolane.

An Economical Route to Lamivudine Featuring a Novel Strategy for Stereospecific Assembly

An economical synthesis of lamivudine was developed by employing a new method to establish the stereochemistry about the heterocyclic oxathiolane ring. Toward this end, an inexpensive and readily accessible lactic acid derivative served the dual purpose of activating the carbohydrate’s anomeric center for N-glycosylation and transferring stereochemical information to the substrate simultaneously. Both enantiomers of the lactic acid derivative are available, and either β-enantiomer in this challenging class of 2′-deoxynucleoside active pharmaceutical ingredients can be formed.

Landscape and opportunities for active pharmaceutical ingredient manufacturing in developing African economies

This review will highlight the opportunities that exist in the localization of cutting-edge manufacturing technologies within an African context.

Levetiracetam+nonsteroidal anti-inflammatory drug binary systems: A contribution to the development of new solid dosage forms

A study has been carried out of binary solid systems made up of the antiepileptic drug levetiracetam, LEV, and a nonsteroidal anti-inflammatory drug, NSAID, capable of managing the inflammation that accompanies epileptic activity. One aim of this research was to identify eutectic mixtures and co-crystals, which are able to impact positively on their biopharmaceutical properties. The NSAIDs studied are (S)- and (R,S)-ibuprofen, (S)- and (R,S)-naproxen, (R,S)-ketoprofen and (R,S)-flurbiprofen, all class II in the Biopharmaceutical Classification System. A green mechanochemical methodology has been used to prepare binary mixtures with different molar ratios, and the binary solid-liquid phase diagrams established. For LEV+(S)-ibuprofen, formation of a single (1:1) co-crystal was confirmed; this was found to melt incongruently. The co-crystal was found to be stable in accelerated stability tests. For the other systems, interesting eutectic mixtures were identified, which showed enhanced dissolution rates of the NSAID relative to the pure drug. For LEV+(R,S)-ibuprofen, LEV+(S)-naproxen and LEV+(R,S)-naproxen, the eutectic mixture compositions have the effective doses of both components. All the NSAIDs investigated are chiral, and their racemates are racemic compounds. Levetiracetam, the (S)-enantiomer of etiracetam, was not efficient in enantiomer discrimination, as all the racemic compound structures are present as the prepared solid mixtures.

From discovery to scale-up: α-lipoic acid : nicotinamide co-crystals in a continuous oscillatory baffled crystalliser

Discovery, characterisation and scale-up of novel α-lipoic acid co-crystals using continuous crystallisation in a COBC is demonstrated.

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

This review which is the second in this series summarises the most common synthetic routes as applied to the preparation of many modern pharmaceutical compounds categorised as containing a six-membered heterocyclic ring. The reported examples are based on the top retailing drug molecules combining synthetic information from both scientific journals and the wider patent literature. It is hoped that this compilation, in combination with the previously published review on five-membered rings, will form a comprehensive foundation and reference source for individuals interested in medicinal, synthetic and preparative chemistry.

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

This review which is the second in this series summarises the most common synthetic routes as applied to the preparation of many modern pharmaceutical compounds categorised as containing a six-membered heterocyclic ring. The reported examples are based on the top retailing drug molecules combining synthetic information from both scientific journals and the wider patent literature. It is hoped that this compilation, in combination with the previously published review on five-membered rings, will form a comprehensive foundation and reference source for individuals interested in medicinal, synthetic and preparative chemistry.

Efficient asymmetric synthesis of lamivudine via enzymatic dynamic kinetic resolution

The anti-HIV nucleoside lamivudine was asymmetrically synthesized in only three steps via a novel surfactant-treated subtilisin Carlsberg-catalyzed dynamic kinetic resolution protocol.

Lamivudine hemihydrate

A new lamivudine hydrate, namely, cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)pyrimidin-2(1H)-one hemihydrate, C(8)H(11)N(3)O(3)S.0.5H(2)O, has been synthesized and structurally characterized by both powder and single-crystal X-ray diffraction studies. The hemihydrate crystallizes in the Sohnke space group P2(1), with the asymmetric unit comprising four lamivudine and two water molecules. An extensive network of intermolecular hydrogen bonds involving both lamivudine and solvent water molecules generates a three-dimensional supramolecular architecture. The structural data and crystal packing of the present lamivudine hemihydrate are compared with those of other hydrated and anhydrous forms of lamivudine.

Ammonium [(1S)-(endo,anti)]-(-)-3-bromo-camphor-8-sulfonate

In the title mol-ecular salt, NH(4) (+)·C(10)H(14)BrO(4)S(-), the norbornane skeleton of the anion is composed of two five-membered rings in envelope conformations and a six-membered ring with one Br atom, one carbonyl O atom and a methyl group held in a boat conformation by a bridging methyl-ene group. Short intra-molecular C-H⋯O and C-H⋯Br inter-actions occur. In the crystal, the component ions are linked by inter-molecular N-H⋯O and C-H⋯O hydrogen bonds.