Highly Regioselective Synthesis of 3′-O-Acyl-Trifluridines Catalyzed by Pseudomonas cepacia Lipase

Biocatalyzed Synthesis of Glycostructures with Anti-infective Activity

Molecules containing carbohydrate moieties play essential roles in fighting a variety of bacterial and viral infections. Consequently, the design of new carbohydrate-containing drugs or vaccines has attracted great attention in recent years as means to target several infectious diseases.Conventional methods to produce these compounds face numerous challenges because their current production technology is based on chemical synthesis, which often requires several steps and uses environmentally unfriendly reactants, contaminant solvents, and inefficient protocols. The search for sustainable processes such as the use of biocatalysts and eco-friendly solvents is of vital importance. Therefore, their use in a variety of reactions leading to the production of pharmaceuticals has increased exponentially in the last years, fueled by recent advances in protein engineering, enzyme directed evolution, combinatorial biosynthesis, immobilization techniques, and flow biocatalysis. In glycochemistry and glycobiology, enzymes belonging to the families of glycosidases, glycosyltransferases (Gtfs), lipases, and, in the case of nucleoside and nucleotide analogues, also nucleoside phosphorylases (NPs) are the preferred choices as catalysts.In this Account, on the basis of our expertise, we will discuss the recent biocatalytic and sustainable approaches that have been employed to synthesize carbohydrate-based drugs, ranging from antiviral nucleosides and nucleotides to antibiotics with antibacterial activity and glycoconjugates such as neoglycoproteins (glycovaccines, GCVs) and glycodendrimers that are considered as very promising tools against viral and bacterial infections.In the first section, we will report the use of NPs and N-deoxyribosyltransferases for the development of transglycosylation processes aimed at the synthesis of nucleoside analogues with antiviral activity. The use of deoxyribonucleoside kinases and hydrolases for the modification of the sugar moiety of nucleosides has been widely investigated.Next, we will describe the results obtained using enzymes for the chemoenzymatic synthesis of glycoconjugates such as GCVs and glycodendrimers with antibacterial and antiviral activity. In this context, the search for efficient enzymatic syntheses represents an excellent strategy to produce structure-defined antigenic or immunogenic oligosaccharide analogues with high purity. Lipases, glycosidases, and Gtfs have been used for their preparation.Interestingly, many authors have proposed the use Gtfs originating from the biosynthesis of natural glycosylated antibiotics such as glycopeptides, macrolides, and aminoglycosides. These have been used in the chemoenzymatic semisynthesis of novel antibiotic derivatives by modification of the sugar moiety linked to their complex scaffold. These contributions will be described in the last section of this review because of their relevance in the fight against the spreading phenomenon of antibiotic resistance. In this context, the pioneering in vivo synthesis of novel derivatives obtained by genetic manipulation of producer strains (combinatorial biosynthesis) will be shortly described as well.All of these strategies provide a useful and environmentally friendly synthetic toolbox. Likewise, the field represents an illustrative example of how biocatalysis can contribute to the sustainable development of complex glycan-based therapies and how problems derived from the integration of natural tools in synthetic pathways can be efficiently tackled to afford high yields and selectivity. The use of enzymatic synthesis is becoming a reality in the pharmaceutical industry and in drug discovery to rapidly afford collections of new antibacterial or antiviral molecules with improved specificity and better metabolic stability.

Immobilized Fe3O4-Polydopamine-Thermomyces lanuginosus Lipase-Catalyzed Acylation of Flavonoid Glycosides and Their Analogs: An Improved Insight Into Enzymic Substrate Recognition

The conversion of flavonoid glycosides and their analogs to their lipophilic ester derivatives was developed by nanobiocatalysts from immobilizing Thermomyces lanuginosus lipase (TLL) on polydopamine-functionalized magnetic Fe3O4 nanoparticles (Fe3O4-PDA-TLL). The behavior investigation revealed that Fe3O4-PDA-TLL exhibits a preference for long chain length fatty acids (i.e., C10 to C14) with higher reaction rates of 12.6-13.9 mM/h. Regarding the substrate specificity, Fe3O4-PDA-TLL showed good substrate spectrum and favorably functionalized the primary OH groups, suggesting that the steric hindrances impeded the secondary or phenolic hydroxyl groups of substrates into the bonding site of the active region of TLL to afford the product.

Biocatalyst-mediated selective acylation and deacylation chemistry on the secondary hydroxyl/amine groups of nucleosides

Nucleosides play a pivotal role in biological systems and therefore have attracted a lot of interest as chemotherapeutic agents in drug discovery. Over the years biocatalysts have emerged as a sustainable alternative to conventional synthetic catalysts. As a nature's catalyst, they exhibit excellent selectivity, remarkable tolerance, and help in carrying out eco-friendly benign processes. The use of a biocatalyst as a regio- and enantioselective catalyst is particularly relevant in the transformations of nucleosides and their analogs because of the presence of multiple chiral centres. Herein, we discuss the recent advances in the Pseudomonas Cepacia Lipase mediated selective acylation and deacylation reactions of the secondary hydroxyl and amino groups of nucleosides and their analogs.

Prodrugs, phospholipids and vesicular delivery - An effective triumvirate of pharmacosomes

With the advent from the laboratory bench to patient bedside in last five decades, vesicular systems have now come to be widely accepted as pragmatic means for controlled delivery of drugs. Their success stories include those of liposomes, niosomes and even the lately developed ethosomes and transferosomes. Pharmacosomes, which, as delivery systems offer numerous advantages and have been widely researched, however, remain largely unacknowledged as a successful delivery system. Though a large number of drugs have been derivatized and formulated into self-assembled vesicular systems, the term pharmacosomes has not been widely used while reporting them. Therefore, their relative obscurity may be attributed to the non-usage of the nomenclature of pharmacosomes by the researchers working in the area. We present a review on the scenario that lead to origin of these bio-inspired vesicles composed of self-assembling amphiphilic molecules. Various drugs that have been formulated into pharmacosomes, their characterization techniques, their properties relative to those of other vesicular delivery systems, and the success achieved so far are also discussed.

Controlled drug release through regulated biodegradation of poly(lactic acid) using inorganic salts

Biodegradation rate of poly(lactic acid) (PLA) has been regulated, both increase and decrease with respect to the biodegradation of pure PLA, by embedding meager amount of inorganic salts in polymer matrix. Biodegradation is performed in enzyme medium on suspension and film and the extent of biodegradation is measured through spectroscopic technique which is also verified by weight loss measurement. Media pH has been controlled using trace amount of inorganic salt which eventually control the biodegradation of PLA. High performance liquid chromatography confirms the hydrolytic degradation of PLA to its monomer/oligomer. Induced pH by metal salts show maximum degradation at alkaline range (with calcium salt) while inhibition is observed in acidic medium (with iron salt). The pH of media changes the conformation of enzyme which in turn regulate the rate of biodegradation. Thermal degradation and increment of modulus indicate improvement in thermo-mechanical properties of PLA in presence of inorganic salts. Functional stability of enzyme with metal salts corresponding to acidic and alkaline pH has been established through a model to explain the conformational changes of the active sites of enzyme at varying pH influencing the rate of hydrolysis leading to regulated biodegradation of PLA. The tuned biodegradation has been applied for the controlled release of drug from the polymer matrix (both sustained and enhanced cumulative release as compared to pure polymer). The cell proliferation and adhesion are influenced by the acidic and basic nature of polymeric material tuned by two different inorganic salts showing better adhesion and proliferation in calcium based composite and, therefore, suggest biological use of these composites in biomedical applications.

The halo-substituent effect on Pseudomonas cepacia lipase-mediated regioselective acylation of nucleosides: A comparative investigation

In this work, comparative experiments were explored to investigate the substrate specificity of Pseudomonas cepacia lipase in regioselective acylation of nucleosides carrying various substituents (such as the H, F, Cl, Br, I) at 2'- and 5-positions. Experimental data indicated that the catalytic performance of the enzyme depended very much on the halo-substituents in nucleosides. The increased bulk of 2'-substituents in ribose moiety of the nucleoside might contribute to the improved 3'-regioselectivity (90-98%, nucleosides a-d) in enzymatic decanoylation, while the enhancement of regioselectivity (93-99%) in 3'-O-acylated nucleosides e-h could be attributable to the increasing hydrophobicity of the halogen atoms at 5-positions. With regard to the chain-length selectivity, P. cepacia lipase displayed the highest 3'-regioselectivity toward the longer chain (C14) as compared to shorter (C6 and C10) ones. The position, orientation and property of the substituent, specific structure of the lipase's active site, and acyl structure could account for the diverse results.

Biocatalytic approaches applied to the synthesis of nucleoside prodrugs

Nucleosides are valuable bioactive molecules, which display antiviral and antitumour activities. Diverse types of prodrugs are designed to enhance their therapeutic efficacy, however this strategy faces the troublesome selectivity issues of nucleoside chemistry. In this context, the aim of this review is to give an overview of the opportunities provided by biocatalytic procedures in the preparation of nucleoside prodrugs. The potential of biocatalysis in this research area will be presented through examples covering the different types of nucleoside prodrugs: nucleoside analogues as prodrugs, nucleoside lipophilic prodrugs and nucleoside hydrophilic prodrugs.