Improved Synthesis of a Novel Biodegradable Tunable Micellar Polymer Based on Partially Hydrogenated Poly(β-malic Acid-co-benzyl Malate)

Poly(benzyl malate) (PBM), together with its derivatives, have been studied as nanocarriers for biomedical applications due to their superior biocompatibility and biodegradability. The acquisition of PBM is primarily from chemical routes, which could offer polymer-controlled molecular weight and a unique controllable morphology. Nowadays, the frequently used synthesis from L-aspartic acid gives an overall yield of 4.5%. In this work, a novel synthesis route with malic acid as the initiator was successfully designed and optimized, increasing the reaction yield up to 31.2%. Furthermore, a crystalline form of PBM (PBM-2) that polymerized from high optical purity benzyl-β-malolactonate (MLABn) was discovered during the optimization process. X-ray diffraction (XRD) patterns revealed that the crystalline PBM-2 had obvious diffraction peaks, demonstrating that its internal atoms were arranged in a more orderly manner and were different from the amorphous PBM-1 prepared from the racemic MLABn. The differential scanning calorimetry (DSC) curves and thermogravimetric curves elucidated the diverse thermal behaviors between PBM-1 and PBM-2. The degradation curves and scanning electron microscopy (SEM) images further demonstrated the biodegradability of PBM, which have different crystal structures. The hardness of PBM-2 implied the potential application in bone regeneration, while it resulted in the reduction of solubility when compared with PBM-1, which made it difficult to be dissolved and hydrogenated. The solution was therefore heated up to 75 °C to achieve benzyl deprotection, and a series of partially hydrogenated PBM was sequent prepared. Their optimal hydrogenation rates were screened to determine the optimal conditions for the formation of micelles suitable for drug-carrier applications. In summary, the synthesis route from malic acid facilitated the production of PBM for a shorter time and with a higher yield. The biodegradability, biosafety, mechanical properties, and adjustable hydrogenation widen the application of PBM with tunable properties as drug carriers.

Organocatalytic Asymmetric Michael Addition in Aqueous Media by a Hydrogen-Bonding Catalyst and Application for Inhibitors of GABAB Receptor

Catalysts based on (R, R)-1,2-diphenylethylenediamine are, as chiral organic catalysts, applied to the asymmetric Michael addition to α, β-unsaturated nitroalkenes under neutral conditions. The role of an aqueous medium for organic catalytic activity can be reversed concerning hydrophilic-hydrophobic function depending on the reaction conditions. In this study, to provide an environmentally friendly system, the thiourea-based catalyst substituted with 3,5-(CF3)2-Ph was used in water solvents. The hydrophobic effect of the substituent provided fast reaction, high chemical yield, and mirror-image selectivity. This reaction allowed the preparation of GABAB agonists in an optically pure manner. Additionally, GABA (γ-aminobutyric acid) analogs such as baclofen and phenibut were synthesized as R-type S-type with high optical purity.

A Reliable Enantioselective Route to Mono-Protected N1-Cbz Piperazic Acid Building Block

The chiral N1-Cbz, N2-H derivative of the piperazic acid monomer is a valuable building block in the total synthesis of natural products, comprising this nonproteinogenic amino acid. In that context, we wish to report an improved synthetic protocol for the synthesis of both (3R)- and (3S)-piperazic acids bearing the carboxybenzyl protecting group (Cbz) selectively at the N1 position. Our method builds on previously reported protocols, circumventing their potential shortcomings, and optimizing the ultimate selective deprotection at the N2 position, thus, offering an efficient and reproducible pathway to suitably modified piperazates in high optical purity.

Ground-State Destabilization by Active-Site Hydrophobicity Controls the Selectivity of a Cofactor- Free Decarboxylase

<div> <div> <p> </p><div> <div> <div> <p>Bacterial arylmalonate decarboxylase (AMDase) and evolved variants have become a valuable tool with which to access both enantiomers of a broad range of chiral arylaliphatic acids with high optical purity. Yet, the molecular principles responsible for the substrate scope, activity and selectivity of this enzyme are only poorly understood to this day, greatly hampering the predictability and design of improved enzyme variants for specific applications. In this work, empirical valence bond and metadynamics simulations were performed on wild-type AMDase and variants thereof, to obtain a better understanding of the underlying molecular processes determining reaction outcome. Our results clearly reproduce the experimentally observed substrate scope, and support a mechanism driven by ground-state destabilization of the carboxylate group being cleaved by the enzyme. In addition, our results indicate that, in the case of the non-converted or poorly-converted substrates studied in this work, increased solvent exposure of the active site upon binding of these substrates can disturb the vulnerable network of interactions responsible for facilitating the AMDase-catalyzed cleavage of CO2. Finally, our results indicate a switch from preferential cleavage of the pro-(R) to the pro-(S) carboxylate group in the CLG-IPL variant of AMDase for all substrates studied. This appears to be due to the emergence of a new hydrophobic pocket generated by the insertion of the six amino acid substitutions, into which the pro-(S) carboxylate binds. Our results allow insight into the tight interaction network determining AMDase selectivity, which in turn provides guidance for the identification of target residues for future enzyme engineering. </p> </div> </div> </div> </div> </div>

Ground-State Destabilization by Active-Site Hydrophobicity Controls the Selectivity of a Cofactor- Free Decarboxylase

<div> <div> <p> </p><div> <div> <div> <p>Bacterial arylmalonate decarboxylase (AMDase) and evolved variants have become a valuable tool with which to access both enantiomers of a broad range of chiral arylaliphatic acids with high optical purity. Yet, the molecular principles responsible for the substrate scope, activity and selectivity of this enzyme are only poorly understood to this day, greatly hampering the predictability and design of improved enzyme variants for specific applications. In this work, empirical valence bond and metadynamics simulations were performed on wild-type AMDase and variants thereof, to obtain a better understanding of the underlying molecular processes determining reaction outcome. Our results clearly reproduce the experimentally observed substrate scope, and support a mechanism driven by ground-state destabilization of the carboxylate group being cleaved by the enzyme. In addition, our results indicate that, in the case of the non-converted or poorly-converted substrates studied in this work, increased solvent exposure of the active site upon binding of these substrates can disturb the vulnerable network of interactions responsible for facilitating the AMDase-catalyzed cleavage of CO2. Finally, our results indicate a switch from preferential cleavage of the pro-(R) to the pro-(S) carboxylate group in the CLG-IPL variant of AMDase for all substrates studied. This appears to be due to the emergence of a new hydrophobic pocket generated by the insertion of the six amino acid substitutions, into which the pro-(S) carboxylate binds. Our results allow insight into the tight interaction network determining AMDase selectivity, which in turn provides guidance for the identification of target residues for future enzyme engineering. </p> </div> </div> </div> </div> </div>

Transformations of Monoterpenes with the p-Menthane Skeleton in the Enzymatic System of Bacteria, Fungi and Insects

The main objective of this article was to present the possibilities of using the enzymatic system of microorganisms and insects to transform small molecules, such as monoterpenes. The most important advantage of this type of reaction is the possibility of obtaining derivatives that are not possible to obtain with standard methods of organic synthesis or are very expensive to obtain. The interest of industrial centers focuses mainly on obtaining particles of high optical purity, which have the desired biological properties. The cost of obtaining such a compound and the elimination of toxic or undesirable chemical waste is important. Enzymatic reactions based on enzymes alone or whole microorganisms enable obtaining products with a specific structure and purity in accordance with the rules of Green Chemistry.

Ground-State Destabilization by Active-Site Hydrophobicity Controls the Selectivity of a Cofactor- Free Decarboxylase

<div> <div> <p> </p><div> <div> <div> <p>Bacterial arylmalonate decarboxylase (AMDase) and evolved variants have become a valuable tool with which to access both enantiomers of a broad range of chiral arylaliphatic acids with high optical purity. Yet, the molecular principles responsible for the substrate scope, activity and selectivity of this enzyme are only poorly understood to this day, greatly hampering the predictability and design of improved enzyme variants for specific applications. In this work, empirical valence bond and metadynamics simulations were performed on wild-type AMDase and variants thereof, to obtain a better understanding of the underlying molecular processes determining reaction outcome. Our results clearly reproduce the experimentally observed substrate scope, and support a mechanism driven by ground-state destabilization of the carboxylate group being cleaved by the enzyme. In addition, our results indicate that, in the case of the non-converted or poorly-converted substrates studied in this work, increased solvent exposure of the active site upon binding of these substrates can disturb the vulnerable network of interactions responsible for facilitating the AMDase-catalyzed cleavage of CO2. Finally, our results indicate a switch from preferential cleavage of the pro-(R) to the pro-(S) carboxylate group in the CLG-IPL variant of AMDase for all substrates studied. This appears to be due to the emergence of a new hydrophobic pocket generated by the insertion of the six amino acid substitutions, into which the pro-(S) carboxylate binds. Our results allow insight into the tight interaction network determining AMDase selectivity, which in turn provides guidance for the identification of target residues for future enzyme engineering. </p> </div> </div> </div> </div> </div>

Ground-State Destabilization Controls the Selectivity of a Cofactor-Free Decarboxylase

<div> <div> <div> <p>Bacterial arylmalonate decarboxylase (AMDase) and evolved variants have become a valuable tool with which to access both enantiomers of a broad range of chiral arylaliphatic acids with high optical purity. Yet, the molecular principles responsible for the substrate scope, activity and selectivity of this enzyme are only poorly understood to this day, greatly hampering the predictability and design of improved enzyme variants for specific applications. In this work, empirical valence bond simulations were performed on wild-type AMDase and variants thereof, to obtain a better understanding of the underlying molecular processes determining reaction outcome. Our results clearly reproduce the experimentally observed substrate scope, and support a mechanism driven by ground-state destabilization of the carboxylate group being cleaved by the enzyme. In addition, our results indicate that, in the case of the non-converted or poorly-converted substrates studied in this work, increased solvent exposure of the active site upon binding of these substrates can disturb the vulnerable network of interactions responsible for facilitating the AMDase-catalyzed cleavage of CO2. Our results thus allow insight into the tight interaction network determining AMDase selectivity, which in turn provides guidance for the identification of target residues for future enzyme engineering. </p> </div> </div> </div>

Synthesis of the Enantiomers of Thioridazine

Thioridazine, a well-known antipsychotic drug, has shown promising effects on several bacterial strains (including Mycobacterium tuberculosis and methicillin-resistant Staphylococcus aureus). Suppressive effects towards selected cancer cell-lines have also been reported. However, due to adverse effects, the compound is no longer in use for the primary indication. More recent research has demonstrated that these side effects are limited to one of the two enantiomers, (+)-thioridazine. The question arises to whether the beneficial effects of thioridazine are limited to one enantiomer, or if (–)-thioridazine can prove itself to be useful in its pure enantiomeric state. The published procedures on the synthesis of the optically pure enantiomers of thioridazine were found to be unsatisfactory, either due to low optical purity, high cost, or problems scaling up. Herein, we have used an auxiliary-based strategy for the total synthesis of both enantiomers in high optical purity and good overall yield. The strategy can easily be scaled up. Both enantiomers were tested against several bacteria. Comparison of the racemic mixture, (–)-thioridazine and its (+)-antipode revealed that they have the same antimicrobial effects. Thus, the non-toxic enantiomer, (–)-thioridazine, can prove useful in this role and should be investigated further.