Polydimethylsiloxane Organic-Inorganic Composite Drug Reservoir with Gliclazide

A novel organic-inorganic gliclazide-loaded composite bead was developed by an ionic gelation process using acidified CaCl2, chitosan and tetraethylorthosilicate (TEOS) as a crosslinker. The beads were manufactured by crosslinking an inorganic silicone elastomer (-OH terminated polydimethylsiloxane, PDMS) with TEOS at different ratios before grafting onto an organic backbone (Na-alginate) using a 32 factorial experimental design. Gliclazide's encapsulation efficiency (EE%) and drug release over 8 h (% DR 8 h) were set as dependent responses for the optimisation of a pharmaceutical formula (herein referred to as 'G op') by response surface methodology. EE % and %DR 8 h of G op were 93.48% ± 0.19 and 70.29% ± 0.18, respectively. G op exhibited a controlled release of gliclazide that follows the Korsmeyer-Peppas kinetic model (R2 = 0.95) with super case II transport and pH-dependent swelling behaviour. In vitro testing of G op showed 92.17% ± 1.18 cell viability upon testing on C2C12 myoblasts, indicating the compatibility of this novel biomaterial platform with skeletal muscle drug delivery.

Immobilization of aldoxime dehydratases on metal affinity resins and use of the immobilized catalysts for the synthesis of nitriles important in fragrance industry

Nitriles have a wide range of uses as building blocks, solvents, and alternative fuels, but also as intermediates and components of flavors and fragrances. The enzymatic synthesis of nitriles by aldoxime dehydratase (Oxd) is an emerging process with significant advantages over conventional approaches. Here we focus on the immobilization of His-tagged Oxds on metal affinity resins, an approach that has not been used previously for these enzymes. The potential of the immobilized Oxd was demonstrated for the synthesis of phenylacetonitrile (PAN) and E-cinnamonitrile, compounds applicable in the fragrance industry. A comparison of Talon and Ni-NTA resins showed that Ni-NTA with its higher binding capacity was more suitable for the immobilization of Oxd. Immobilized Oxds were prepared from purified enzymes (OxdFv from Fusarium vanettenii and OxdBr1 from Bradyrhizobium sp.) or the corresponding cell-free extracts. The immobilization of cell-free extracts reduced time and cost of the catalyst production. The immobilized OxdBr1 was superior in terms of recyclability (22 cycles) in the synthesis of PAN from 15 mM E/Z-phenylacetaldoxime at pH 7.0 and 30 °C (100% conversion, 61% isolated yield after product purification). The volumetric and catalyst productivity was 10.5 g/L/h and 48.3 g/g of immobilized protein, respectively.

Database-driven In Silico-Identification and Characterization of Novel Aldoxime Dehydratases

Aldoxime dehydratases (Oxds) are a unique class of enzymes, which catalyzes the dehydration of aldoximes to nitriles in an aqueous environment. Recently, they gained attention as a catalyst for a green and cyanide-free alternative to established nitrile syntheses, which often require the use of toxic cyanides and harsh reaction conditions. Up to now only thirteen aldoxime dehydratases have been discovered and biochemically characterized. This raised the interest for identifying further Oxds with, e.g., complementary properties in terms of substrate scope. In this study, 16 novel genes, presumably encoding aldoxime dehydratases, were selected by using a commercially available 3DM database based on OxdB an Oxd from Bacillus sp. OxB-1. Out of 16 proteins, six enzymes with aldoxime dehydratases activity were identified, which differ in their substrate scope and activity. While some novel Oxds showed better performance for aliphatic substrate such as n-octanaloxime compared to the well characterized OxdRE from Rhodococcus sp. N-771, some showed activity for aromatic aldoximes, leading to an overall high usability of these enzymes in organic chemistry. The applicability for organic synthesis was underlined by converting 100 mM n-octanaloxime at a 10 mL scale within 5 h with the novel aldoxime dehydratase OxdHR as whole-cell catalyst (33 mg_bww/mL).

Scanning aldoxime dehydratase sequence space and characterization of a new aldoxime dehydratase from Fusarium vanettenii

The aim of this work was to map the sequence space of aldoxime dehydratases (Oxds) as enzymes with great potential for nitrile synthesis. Microbes contain an abundance of putative Oxds but fewer than ten Oxds were characterized in total and only two in fungi. In this work, we prepared and characterized a new Oxd (protein gb|EEU37245.1 named OxdFv) from Fusarium vanettenii 77-13-4. OxdFv is distant from the characterized Oxds with a maximum of 36% identity. Moreover, the canonical Oxd catalytic triad RSH is replaced by R141-E187-E303 in OxdFv. R141A and E187A mutants did not show significant activities, but mutant E303A showed a comparable activity as the wild-type enzyme. According to native mass spectrometry, OxdFv contained almost 1 mol of heme per 1 mol of protein, and was composed of approximately 88% monomer (41.8 kDa) and 12% dimer. A major advantage of this enzyme is its considerable activity under aerobic conditions (25.0 ± 4.3 U/mg for E,Z-phenylacetaldoxime at pH 9.0 and 55 °C). Addition of sodium dithionite (reducing agent) and Fe²⁺ was required for this activity. OxdFv favored (aryl)aliphatic aldoximes over aromatic aldoximes. Substrate docking in the homology model of OxdFv showed a similar substrate specificity. We conclude that OxdFv is the first characterized Oxd of the REE type.

Novel Silicone-Grafted Alginate as a Drug Delivery Scaffold: Pharmaceutical Characterization of Gliclazide-Loaded Silicone-Based Composite Microcapsules

A novel gliclazide-loaded elastomeric carbohydrate pharmaceutical vehicle was successfully developed. This new siliconized alginate platform showed pseudoplastic rheology with a zeta potential ranging from (-43.8 mV to -75.5 mV). A Buchi-B390 encapsulator was employed to formulate different types of silicone-grafted alginate microcapsules loaded with gliclazide relying on the vibrational ionic gelation technology. The use of tetraethyl orthosilicate (TEOS) to crosslink the silicone elastomer (hydroxy terminated polydimethylsiloxane) of this new platform had improved the gliclazide encapsulation (>92.13% ± 0.76) of the free-flowing composite microcapsules, which showed good mechanical durability (up to 12 h in PBS pH 6.8) and promising results to sustain the drug release.

Cyanide-free synthesis of aromatic nitriles from aldoximes: Discovery and application of a novel heme-containing aldoxime dehydratase

Aromatic nitriles are important structural motifs that frequently existed in pharmaceutical drugs. Due to the convenient synthesis of aldoximes from aldehydes, the dehydration of aldoximes to corresponding nitriles by aldoxime dehydratases (Oxds) is considered as a safe and robust enzymatic production route. Although the Oxd genes are widely distributed in microbial kingdom, so far less than ten Oxds were expressed and further characterized. In this study, we found 26 predicted putative Oxd genes from the GenBank database using a genome mining strategy. The Oxd gene from Pseudomonas putida F1 was cloned and functionally expressed in Escherichia coli BL21 (DE3). The amino acid sequence of OxdF1 shows high identities of 33∼85 % to other characterized Oxds, and contained a ferrous heme as the catalytic site. The optimum reaction pH and temperature of recombinant OxdF1 were 7.0 and 35 °C, respectively. OxdF1 was stable in pH 7.0 potassium phosphate buffer at 30 °C, and its half-life was approximately 3.8 h. OxdF1 can efficiently dehydrate aromatic and heterocyclic aldoximes to nitriles, such as 2-bromobenzaldoxime, 2-chloro-6-fluorobenzaldoxime, thiophene-2-carboxaldoxime, and pyridine-3-aldoxime. Therefore, the recombinant OxdF1 shows a potential application in the cyanide-free synthesis of aromatic nitriles.

Synthetic Processes toward Nitriles without the Use of Cyanide: A Biocatalytic Concept Based on Dehydration of Aldoximes in Water

While belonging to the most fundamental functional groups, nitriles represent a class of compound that still raises challenges in terms of an efficient, cost‐effective, general and, at the same time, sustainable way for their synthesis. Complementing existing chemical routes, recently a cyanide‐free enzymatic process technology based on the use of an aldoxime dehydratase (Oxd) as a biocatalyst component has been developed and successfully applied for the synthesis of a range of nitrile products. In these biotransformations, the Oxd enzymes catalyze the dehydration of aldoximes as readily available substrates to the nitrile products. Herein, these developments with such enzymes are summarized, with a strong focus on synthetic applications. It is demonstrated that this biocatalytic technology has the potential to “cross the bridge” between the production of fine chemicals and pharmaceuticals, on one hand, and bulk and commodity chemicals, on the other.