The ability of lipases to display activity beyond their physiological reactions, so-called “catalytic promiscuity”, has gained increasing interest in the last two decades as an important tool for expanding the application of these enzymes in organic synthesis. Some lipases have been shown to be effective in catalyzing a variety of C-C bond formation reactions and most of the investigations have been directed to the optimization of the products yield through a careful tuning of the experimental parameters. Despite the fact that new stereogenic carbons are formed in many of the tested reactions, the target products have been often obtained in racemic form and examples of an efficient asymmetric induction by the used lipases are quite limited. The aim of this review, mainly focused on those lipase-catalyzed promiscuous reactions in which optically active products have been obtained, is to offer a current state of art together with a perspective in this field of asymmetric synthesis.

In this review the recent reports of biocatalytic reactions applied to the desymmetrization of meso-compounds or symmetric prochiral molecules are summarized. The survey of literature from 2015 up to date reveals that lipases are still the most used enzymes for this goal, due to their large substrate tolerance, stability in different reaction conditions and commercial availability. However, a growing interest is focused on the use of other purified enzymes or microbial whole cells to expand the portfolio of exploitable reactions and the molecular diversity of substrates to be transformed. Biocatalyzed desymmetrization is nowadays recognized as a reliable and efficient approach for the preparation of pharmaceuticals or natural bioactive compounds and many processes have been scaled up for multigram preparative purposes, also in continuous-flow conditions.

Limonene is one of the most abundant naturally occurring cyclic monoterpenes and has recently emerged as a sustainable alternative to petroleum-based solvents as well as a chemical platform for the production of value-added compounds. The biocatalytic epoxidation of both enantiomers of limonene was carried out in the presence of a peroxygenase-containing preparation from oat (Avena sativa) flour. Different reaction profiles were observed depending on the starting enantiomer of limonene, but in both cases the 1,2-monoepoxide was obtained as the main product with excellent diastereoselectivity. Trans-1,2-monoepoxide and cis-1,2-monoepoxide were isolated from the reaction of (R)-limonene and (S)-limonene, respectively, and the reactions were scaled-up to 0.17 M substrate concentration. The process is valuable for operational simplicity, lack of toxic metal catalysts, and cost-effectiveness of the enzymatic source. Pure stereoisomers of 1,2-monoepoxides of limonene constitute a useful starting material for biorenewable polymers, but can be also converted into other chiral derivatives by epoxide ring opening with nucleophiles. As a proof of concept, a tandem protocol for the preparation of enantiopure (1S,2S,4R)-1,2-diol from (R)-limonene and (1R,2R,4S)-1,2-diol from (S)-limonene was developed.

Neuroinflammation is a symptom of different neurodegenerative diseases, and growing interest is directed towards active drug development for the reduction of its negative effects. The anti-inflammatory activity of polyunsaturated fatty acids, eicosapentaenoic (EPA), docosahexaenoic (DHA), and their amide derivatives was largely investigated on some neural cells. Herein, we aimed to elucidate the protective role of both EPA and DHA and the corresponding N-ethanolamides EPA-EA and DHA-EA on neonatal mouse Olfactory Ensheathing Cells (OECs) after exposition to lipopolysaccharide (LPS)-induced neuroinflammation. To verify their anti-inflammatory effect and cell morphological features on OECs, the expression of IL-10 cytokine, and cytoskeletal proteins (vimentin and GFAP) was evaluated by immunocytochemical procedures. In addition, MTT assays, TUNEL, and mitochondrial health tests were carried out to assess their protective effects on OEC viability. Our results highlight a reduction in GFAP and vimentin expression in OECs exposed to LPS and treated with EPA or DHA or EPA-EA or DHA-EA in comparison with OECs exposed to LPS alone. We observed a protective role of EPA and DHA on cell morphology, while the amides EPA-EA and DHA-EA mainly exerted a superior anti-inflammatory effect compared to free acids.

Antarctica can serve as the source of novel extremophilic microorganisms and biomolecules, including extremozymes which could find applications in bioremediation processes for the presence of enzymes able to degrade plastic polymers. Carboxylic ester hydrolases (EC 3.1.1) catalyze the hydrolysis of linear and cyclic ester bonds. Among these, esterases (EC 3.1.1.1) and triacylglycerol lipases (EC 3.1.1.3) have been shown effective in degrading polyester polymers. Two psychrophilic bacterial strains ASPA161_6 and ASPA161_9 were isolated from environmental samples, and their optimal growth conditions were determined. The marine sediment samples were collected at a depth of 20 m in the Antarctic Specially Protected Area n. 161 (74°42' S, 164°07' E, Ross Sea) during the 2017/2018 XXXIII Italian Antarctic expedition. Genomes were sequenced, assembled and annotated. Genes encoding for proteins involved in cold adaptation were searched with an in-silico search approach. Moreover, the sequences of genes involved in the degradation of polyester plastics were studied through the annotation via PlaticDB tool. Esterase and lipase activities were also detected in-plate and quantitatively evaluated at different temperatures on crude protein extracts from the extracellular fraction of the microorganisms using a specific assay based on the hydrolysis of p-nitrophenyl esters. Furthermore, the same fractions were tested onto the polymer polyethylene adipate as a model of biodegradable polyester plastic. The degradation studies with polyethylene adipate were performed following the reaction progress with ¹H NMR. Based on digital DNA-DNA hybridization and average nucleotide identity values, the two new isolates were assigned to the Psychrobacter genus. A comprehensive annotation using PlasticDB revealed substantial degree of similarity in the gene sequences coding for a variety of plastic-degrading enzymes, particularly carboxylic ester hydrolases. However, some differences were observed in the enzymatic profiles of the two bacterial strains, highlighting their versatility and potential for effective biodegradation of a range of plastic polymers. Subsequently, carboxylic ester hydrolases were detected with qualitative in-plate assays with olive oil and tributyrin as substrates. The enzymatic activity of psychrotolerant extracellular esterases and lipases was quantified using chromogenic-spectrophotometric assays. The presence of esterases was assayed against pNP-acetate, and for both strains an optimal activity was detected at 35 °C (0.5 and 0.8 nmol pNP released/mg protein in 30 min for strain ASPA161_6 and strain ASPA161_9, respectively). A significant activity was maintained at lower temperatures, ranging from 50.1 and 71.8 % at 15 and 25 °C for strain ASPA161_6 and from 49.6 and 68.1 % for strain ASPA161_9. These results suggested psychrotolerant characteristics of these enzymes. The presence of lipases was determined with pNP-dodecanoate, resulting in 2.6 and 3.5 nmol pNP released/mg protein at 25 °C in 30 min for the two strains. Most of the activity was retained at 25 °C (73.4 and 66.3 %, respectively), with a decrease at 15 °C (45.3 and 38.6 %), which may be attributed to the reduced kinetic activity. Finally, the degradation experiments with PEA with averaged molar mass 1000 g/mol as a model polyester plastic demonstrated a 55-65 % degradation rate after 12 days of incubation. The obtained data underlined the ability of the investigated strains to express carboxylic ester hydrolases under the specified growth conditions. These findings highlight their biotechnological potential in bioremediation, particularly for sustainable plastic waste management in cold or temperate environments. Future investigations could focus on optimizing enzymatic activity through heterologous expression or utilizing whole-cell systems for direct polymer degradation.