Generation of highly amenable cellulose-Iß via selective delignification of rice straw using a reusable cyclic ether-assisted deep eutectic solvent system.

Cellulolytic enzymes can readily access the cellulosic component of lignocellulosic biomass after the removal of lignin during biomass pretreatment. The enzymatic hydrolysis of cellulose is necessary for generating monomeric sugars, which are then fermented into ethanol. In our study, a combination of a deep eutectic (DE) mixture (of 2-aminoethanol and tetra-n-butyl ammonium bromide) and a cyclic ether (tetrahydrofuran) was used for selective delignification of rice straw (RS) under mild conditions (100 °C). Pretreatment with DE-THF solvent system caused ~ 46% delignification whereas cellulose (~ 91%) and hemicellulose (~ 67%) recoveries remained higher. The new solvent system could be reused upto 10 subsequent cycles with the same effectivity. Interestingly, the DE-THF pretreated cellulose showed remarkable enzymatic hydrolysability, despite an increase in its crystallinity to 72.3%. Contrary to conventional pretreatments, we report for the first time that the enzymatic hydrolysis of pretreated cellulose is enhanced by the removal of lignin during DE-THF pretreatment, notwithstanding an increase in its crystallinity. The current study paves way for the development of newer strategies for biomass depolymerization with DES based solvents.

A novel ternary combination of deep eutectic solvent-alcohol (DES-OL) system for synergistic and efficient delignification of biomass.

A novel ternary system consisting of deep eutectic solvent-alcohol (DES-OL) mixture was developed for the effective delignification of lignocellulosic biomass. Optimization studies included selecting suitable co-solvent (among n-BuOH, n-PrOH & EtOAc) for treating biomass (rice husk, rice straw and wheat straw), altering the DES-to-alcohol ratio (2:1, 1:1 and 1:2) as well as the reaction temperature (50, 80 and 120 °C). The highest delignification (∼50%) was observed using n-butanol assisted DES (ChCl: OA) at a ratio of 2:1, with high solid loading of 15% (w/v) at 120 °C (∼1.2 bar) in a 60 min reaction. Post pretreatment, high purity lignin was recovered after distilling off butanol for recycling. Microscopy and CPMAS/NMR studies confirmed the effectiveness of DES-OL pretreatment on biomass delignification.

Novel alkali-thermostable xylanase from Thielaviopsis basicola (MTCC 1467): Purification and kinetic characterization.

A novel extracellular alkali-thermostable xylanase was purified to an apparent homogeneity from the submerged fermented culture filtrate of Thielaviopsis basicola MTCC 1467, wherein, the fungus was fed with rice straw as prime carbon source. SDS-PAGE analysis of the xylanase showcased molecular weight of ∼ 32 kDa. This extracellular protein macromolecule had maximum xylanolytic activity at pH 5.5 and 60°C, and was stable in the range of pH 5.0-10.0 for 5 days retaining >70% activity. The enzyme was stable at 30-50°C for 5h retaining >85% activity and further by retaining 70% activity at 60°C for 2h. The enzyme deactivation constants (kd) were in range of 0.41-1.3. The kinetic experiments specified that the enzyme had Km and Vmax values of 1.447 ± 0.22 mg mL(-1) and 60.04 ± 1.25 IU mL(-1), respectively, for xylan. The purified xylanase was significantly inhibited by Cu(2+) and Zn(2+) (∼ 58%), whilst Ca(2+) and Na(+) ions displayed partial inhibition (<8%) Intriguingly, the K(+) and Mn(2+) ions enhanced the activity by about ∼ 10%. Both SDS and EDTA reduced its activity by ∼ 20%.

Design, synthesis and biological evaluation of small molecules as potent glucosidase inhibitors.

Herein we have reported design, synthesis and in vitro biological evaluation of a library of bicyclic lactams that led to the discovery of compounds 6 and 7 as a novel class of α-glucosidase inhibitors. They inhibited α-glucosidase (yeast origin) in a mixed type of inhibition with an IC50 of ∼150 nM. Molecular docking studies further substantiated screening results. Interestingly phenotypic screening of this library against the human malaria parasite revealed 7 as a potent antiplasmodial agent.

Development of α-glucosidase inhibitors by room temperature C-C cross couplings of quinazolinones.

Novel quinazolinone based α-glucosidase inhibitors have been developed. For this purpose a virtual screening model has been generated and validated utilizing acarbose as a α-glucosidase inhibitor. Homology modeling, docking, and virtual screening were successfully employed to discover a set of structurally diverse compounds active against α-glucosidase. A search of a 3D database containing 22,500 small molecules using the structure based virtual model yielded ten possible candidates. All ten candidates were N-3-pyridyl-2-cyclopropyl quinazolinone-4-one derivatives, varying at the 6 position. This position was modified by Suzuki-Miyaura cross coupling with aryl, heteroaryl, and alkyl boronic acids. A catalyst screen was performed, and using the best optimal conditions, a series of twenty five compounds was synthesized. Notably, the C-C cross coupling reactions of the 6-bromo-2-cyclopropyl-3-(pyridyl-3-ylmethyl)quinazolin-4(3H)-one precursor have been accomplished at room temperature. A comparison of the relative reactivities of 6-bromo and 6-chloro-2,3-disubstituted quinazolinones with phenyl boronic acid was conducted. An investigation of pre-catalyst loading for the reaction of the 6-bromo-2-cyclopropyl-3-(pyridyl-3-ylmethyl)quinazolin-4(3H)-one substrate was also carried out. Finally, we submitted our compounds to biological assays against α-glucosidase inhibitors. Of these, three hits (compounds 4a, 4t and 4r) were potentially active as α-glucosidase inhibitors and showed activity with IC50 values <20 µM. Based on structural novelty and desirable drug-like properties, 4a was selected for structure-activity relationship study, and thirteen analogs were synthesized. Nine out of thirteen analogs acted as α-glucosidase inhibitors with IC50 values <10 µM. These lead compounds have desirable physicochemical properties and are excellent candidates for further optimization.

Synthesis of privileged scaffolds by using diversity-oriented synthesis.

An elegant reagent-controlled strategy has been developed for the generation of a diverse range of biologically active scaffolds from a chiral bicyclic lactam. Reduction of the chiral lactam with LAH or alkylation with LHMDS to trigger different cyclization reactions have been shown to generate privileged scaffolds, such as pyrrolidines, indolines, and cyclotryptamines. Their amenability to substitution allows us to create various compound libraries by using these scaffolds. In silico studies were used to estimate the drug-like properties of these compounds. Selected compounds were subjected to anticancer screening by using three different cell lines. In addition, all these compounds were subjected to antibacterial screening to gauge the spectrum of biological activity that was conferred by our DOS methodology. Gratifyingly, with no additional iterative cycles, our method directly generated anticancer compounds with potency at low nanomolar concentrations, as represented by spiroindoline 14.

Potential of thermo and alkali stable xylanases from Thielaviopsis basicola (MTCC-1467) in biobleaching of wood kraft pulp.

Thermo- and alkali-stable xylanases produced from Thielaviopsis basicola (MTCC-1467) on low-cost carbon source like rice straw were evaluated for their potential application in biobleaching of wood kraft pulp. Enzyme treatment at retention time of 240 min with 20 IU/gm of dried pulp resulted in ~85.2 % of reduction in kappa number. When compared to control, 110.8, 93, and 72.2 % of enhancement in brightness (percent International Organization of Standardization), whiteness, and fluorescence, respectively, were observed for enzyme-treated pulp. Spectroscopic analysis showed significant release of chromophoric compounds from enzyme-treated pulp. Furthermore, scanning electron microscope studies of unbleached and enzyme bleached pulp revealed the effectiveness of enzymatic treatment. The enzyme-treated pulp subjected to later stages of chemical bleaching resulted in 16 % decrease in chlorine consumption along with considerable reduction in chemical oxygen demand percentage (14.5 %) level of effluent. Various pulp properties like fiber length, fiber width, burst strength, burst index, tear strength, tear index, tensile strength, and breaking length were also significantly improved after enzyme treatment when compared to control.