Polyesters from Macrolactones Using Commercial Lipase NS 88011 and Novozym 435 as Biocatalysts

Collagen-decorated electrospun scaffolds of unsaturated copolyesters for bone tissue regeneration

Many efforts have been devoted to bone tissue to regenerate damaged tissues, and the development of new biocompatible materials that match the biological, mechanical, and chemical features required for this application is crucial. Herein, a collagen-decorated scaffold was prepared via electrospinning using a synthesized unsaturated copolyester (poly(globalide-co-pentadecalactone)), followed by two coupling reactions: thiol-ene functionalization with cysteine and further conjugation via EDC/NHS chemistry with collagen, aiming to design a bone tissue regeneration device with improved hydrophilicity and cell viability. Comonomer ratios were varied, affecting the copolymer's thermal and chemical properties and highlighting the tunable features of this copolyester. Functionalization with cysteine created new carboxyl and amine groups needed for bioconjugation with collagen, which is responsible for providing biological and structural integrity to the extra-cellular matrix. Bioconjugation with collagen turned the scaffold highly hydrophilic, decreasing its contact angle from 107 ± 2° to 0°, decreasing the copolymer crystallinity by 71%, and improving cell viability by 85% compared with the raw scaffold, thus promoting cell growth and proliferation. The highly efficient and biosafe strategy to conjugate polymers and proteins created a promising device for bone repair in tissue engineering.

Simple magnesium alkoxides: synthesis, molecular structure, and catalytic behaviour in the ring-opening polymerization of lactide and macrolactones and in the copolymerization of maleic anhydride and propylene oxide

The synthesis of two chiral bulky alkoxide pro-ligands, 1-adamantyl-tert-butylphenylmethanol HOCAdtBuPh and 1-adamantylmethylphenylmethanol HOCAdMePh, is reported and their coordination chemistry with magnesium(II) is described and compared with the coordination chemistry of the previously reported achiral bulky alkoxide pro-ligand HOCtBu2Ph. Treatment of n-butyl-sec-butylmagnesium with two equivalents of the racemic mixture of HOCAdtBuPh led selectively to the formation of the mononuclear bis(alkoxide) complex Mg(OCAdtBuPh)2(THF)2. 1H NMR spectroscopy and X-ray crystallography suggested the selective formation of the C2-symmetric homochiral diastereomer Mg(OCRAdtBuPh)2(THF)2/Mg(OCSAdtBuPh)2(THF)2. In contrast, the less sterically encumbered HOCAdMePh led to the formation of dinuclear products indicating only partial alkyl group substitution. The mononuclear Mg(OCAdtBuPh)2(THF)2 complex was tested as a catalyst in different reactions for the synthesis of polyesters. In the ROP of lactide, Mg(OCAdtBuPh)2(THF)2 demonstrated very high activity, higher than that shown by Mg(OCtBu2Ph)2(THF)2, although with moderate control degrees. Both Mg(OCAdtBuPh)2(THF)2 and Mg(OCtBu2Ph)2(THF)2 were found to be very effective in the polymerization of macrolactones such as ω-pentadecalactone (PDL) and ω-6-hexadecenlactone (HDL) also under mild reaction conditions that are generally prohibitive for these substrates. The same catalysts demonstrated efficient ring-opening copolymerization (ROCOP) of propylene oxide (PO) and maleic anhydride (MA) to produce poly(propylene maleate).

Production of lactones for flavoring and pharmacological purposes from unsaturated lipids: an industrial perspective

The enantiomeric pure and natural (+)-Lactones (C ≤ 14) with aromas obtained from fruits and milk are considered flavoring compounds. The flavoring value is related to the lactones' ring size and chain length, which blend in varying concentrations to produce different stone-fruit flavors. The nature-identical and enantiomeric pure (+)-lactones are only produced through whole-cell biotransformation of yeast. The industrially important γ-decalactone and δ-decalactone are produced by a four-step aerobic-oxidation of ricinoleic acid (RA) following the lactonization mechanism. Recently, metabolic engineering strategies have opened up new possibilities for increasing productivity. Another strategy for increasing yield is to immobilize the RA and remove lactones from the broth regularly. Besides flavor impact, γ-, δ-, ε-, ω-lactones of the carbon chain (C8-C12), the macro-lactones and their derivatives are vital in pharmaceuticals and healthcare. These analogues are isolated from natural sources or commercially produced via biotransformation and chemical synthesis processes for medicinal use or as active pharmaceutical ingredients. The various approaches to biotransformation have been discussed in this review to generate more prospects from a commercial point of view. Finally, this work will be regarded as a magical brick capable of containing both traditional and genetic engineering technology while contributing to a wide range of commercial applications.

Prospects of Using Biocatalysis for the Synthesis and Modification of Polymers

Trends in the dynamically developing application of biocatalysis for the synthesis and modification of polymers over the past 5 years are considered, with an emphasis on the production of biodegradable, biocompatible and functional polymeric materials oriented to medical applications. The possibilities of using enzymes not only as catalysts for polymerization but also for the preparation of monomers for polymerization or oligomers for block copolymerization are considered. Special attention is paid to the prospects and existing limitations of biocatalytic production of new synthetic biopolymers based on natural compounds and monomers from biomass, which can lead to a huge variety of functional biomaterials. The existing experience and perspectives for the integration of bio- and chemocatalysis in this area are discussed.

Main Structural Targets for Engineering Lipase Substrate Specificity

Microbial lipases represent one of the most important groups of biotechnological biocatalysts. However, the high-level production of lipases requires an understanding of the molecular mechanisms of gene expression, folding, and secretion processes. Stable, selective, and productive lipase is essential for modern chemical industries, as most lipases cannot work in different process conditions. However, the screening and isolation of a new lipase with desired and specific properties would be time consuming, and costly, so researchers typically modify an available lipase with a certain potential for minimizing cost. Improving enzyme properties is associated with altering the enzymatic structure by changing one or several amino acids in the protein sequence. This review detailed the main sources, classification, structural properties, and mutagenic approaches, such as rational design (site direct mutagenesis, iterative saturation mutagenesis) and direct evolution (error prone PCR, DNA shuffling), for achieving modification goals. Here, both techniques were reviewed, with different results for lipase engineering, with a particular focus on improving or changing lipase specificity. Changing the amino acid sequences of the binding pocket or lid region of the lipase led to remarkable enzyme substrate specificity and enantioselectivity improvement. Site-directed mutagenesis is one of the appropriate methods to alter the enzyme sequence, as compared to random mutagenesis, such as error-prone PCR. This contribution has summarized and evaluated several experimental studies on modifying the substrate specificity of lipases.

The Effectively Simultaneous Production of Cello-oligosaccharide and Glucose Mono-decanoate from Lignocellulose by Enzymatic Esterification

Cello-oligosaccharide has drawn an increasing attention as the nutritional ingredients of dietary supplements, whose quality is affected by the concentration of monosaccharide. In the present study, an effective process was developed for the simultaneous production of cello-oligosaccharide and glucose mono-decanoate from lignocellulose by enzymatic esterification. During the process, the excessive glucose in cello-oligosaccharide was converted into glucose mono-decanoate, which is a well-known biodegradable nonionic surfactant. The filter paper was initially used as the model to investigate the feasibility of the process, in which the purity of resultant cello-oligosaccharide was increased from 33.3% to 74.3%, simultaneously producing glucose mono-decanoate with a purity of 92.3%. Further verification of 3 kinds of lignocelluloses (switchgrass, cornstalk, and reed) also indicated a good performance of the process. The present process provided an effective strategy to increase the purity of resultant cello-oligosaccharide with the simultaneous production of high value-added products of sugar monoester. Graphical Abstract Simultaneous production of cello-oligosaccharide and glucose mono-decanoate from lignocellulose.

Copolymacrolactones Grafted with l-Glutamic Acid: Synthesis, Structure, and Nanocarrier Properties

The enzymatic ring-opening copolymerization (eROP) of globalide (Gl) and pentadecalactone (PDL) was performed in solution from mixtures of the two macrolactones at ratios covering the whole range of comonomeric compositions. The resulting P(Glx-r-PDLy) random copolyesters were aminofunctionalized by thiol-ene reaction with aminoethanethiol. ROP of γ-benzyl-l-glutamate N-carboxyanhydride initiated by P(Glx-r-PDLy)-NH2 provided neutral poly(γ-benzyl-l-glutamate)-grafted copolyesters, which were converted by hydrolysis into negatively charged hybrid copolymers. Both water-soluble and nonsoluble copolymers were produced depending on copolymer charge and their grafting degree, and their capacity for self-assembling in nano-objects were comparatively examined. The emulsion solvent-evaporation technique applied to the chloroform-soluble copolymers grafted with benzyl glutamate rendered well-delineated spherical nanoparticles with an average diameter of 200-300 nm. Conversely, micellar solutions in water were produced from copolyesters bearing grafted chains composed of at least 10 units of glutamic acid in the free form. The copolymer micelles were shown to be able to load doxorubicin (DOX) efficiently through electrostatic interactions and also to release the drug at a rate that was markedly pH dependent.

Crosslinking of Electrospun Fibres from Unsaturated Polyesters by Bis-Triazolinediones (TAD)

Crosslinking of an unsaturated aliphatic polyester poly(globalide) (PGl) by bistriazolinediones (bisTADs) is reported. First, a monofunctional model compound, phenyl-TAD (PTAD), was tested for PGl functionalisation. 1H-NMR showed that PTAD-ene reaction was highly efficient with conversions up to 97%. Subsequently, hexamethylene bisTAD (HM-bisTAD) and methylene diphenyl bisTAD (MDP-bisTAD) were used to crosslink electrospun PGl fibres via one- and two-step approaches. In the one-step approach, PGl fibres were collected in a bisTAD solution for in situ crosslinking, which resulted in incomplete crosslinking. In the two-step approach, a light crosslinking of fibres was first achieved in a PGl non-solvent. Subsequent incubation in a fibre swelling bisTAD solution resulted in fully amorphous crosslinked fibres. SEM analysis revealed that the fibres' morphology was uncompromised by the crosslinking. A significant increase of tensile strength from 0.3 ± 0.08 MPa to 2.7 ± 0.8 MPa and 3.9 ± 0.5 MPa was observed when PGI fibres were crosslinked by HM-bisTAD and MDP-bisTAD, respectively. The reported methodology allows the design of electrospun fibres from biocompatible polyesters and the modulation of their mechanical and thermal properties. It also opens future opportunities for drug delivery applications by selected drug loading.

Enzymatic Synthesis of a Diene Ester Monomer Derived from Renewable Resource

The total or partial substitution of fossil raw materials by biobased materials from renewable resources is one of the great challenges of our society. In this context, the reaction under mild condition as enzyme-catalyzed esterification was applied to investigate the esterification of the biobased 10-undecenoic acid with 2-hydroxyethyl methacrylate (HEMA) to obtain a new diene ester monomer. The environmentally friendly enzymatic reaction presented up to 100% of conversion; moreover, the production of possible by-products was minimized controlling reaction time and amount of enzyme. Furthermore, the presence of chloroform was evaluated during the enzymatic reactions and despite high conversions with higher enzyme concentration, the solvent-free system showed fast kinetics even with 1.13 U/g substrates. In addition, the commercial immobilized lipases Novozym 435 and NS 88011 could be applied for up to 10 cycles keeping conversions about 90%. The scale-up of the reaction was possible and a purification procedure was applied in order to isolate the diene ester monomer 2-(10-undecenoyloxy)ethyl methacrylate, preserving its double bonds, which could allow a potential use of this product in the synthesis of new renewable polymers through techniques as metathesis, thiol-ene, or free-radical polymerization.

Lipase-catalyzed synthesis of ethyl (R)-2-benzyloxy-2-isopropylhydrogenmalonate: a useful combination of chemical synthesis with enzymatic methods

Ethyl (R)-2-benzyloxy-2-isopropylhydrogenmalonate is a key intermediate for the synthesis of the side chain in ergopeptines. In this work, we adopted a method to prepare enantiomerically pure title monoester via immobilized Candida antarctica lipase B (Novozym 435)-catalyzed hydrolysis of the corresponding diester.

Enantio-, Regio-, and Chemoselective Lipase-Catalyzed Polymer Synthesis

In contrast to chemical routes, enzymatic polymerization possesses favorable characteristics of mild reaction conditions, few by-products, and high activity toward cyclic lactones which make it a promising technique for constructing polymeric materials. Meanwhile, it can avoid the trace residue of metallic catalysts and potential toxicity, and thus exhibits great potential in the biomedical fields. More importantly, lipase-catalyzed polymer synthesis usually shows favorable enantio-, regio-, and chemoselectivity. Here, the history and recent developments in lipase-catalyzed selective polymerization for constructing polymers with unique structures and properties are highlighted. In particular, the synthesis of polymeric materials which are difficult to prepare in a chemical route and the construction of polymers through the combination of selective enzymatic and chemical methods are focused. In addition, the future direction is proposed especially based on the rapid developments in computational chemistry and protein engineering techniques.