Hydroxymethyl Research Articles

Quantum Chemical Investigation into the Structural Analysis and Calculated Raman Spectra of Amylose Modeled with Linked Glucose Molecules.

This study presents a quantum chemical investigation into the structural analysis and calculated Raman spectra of modeled amylose with varying units of linked glucose molecules. We systematically examined the rotation of hydroxymethyl groups and intramolecular hydrogen bonds within these amylose models. Our study found that as the number of linked glucose units increases, the linear structure becomes more complex, resulting in curled, cyclic, or helical structures facilitated by establishing various intramolecular interactions. The hydroxymethyl groups were confirmed to form interactions with oxygen atoms and with hydroxymethyl and hydroxyl groups from adjacent rings in the molecular structures. We identified distinct peaks and selected specific bands applicable in various analytical contexts by comparing their calculated Raman spectra. Representative vibrational modes within selected regions were identified across the different lengths of amylose models, serving as characteristic signatures for linear and more coiled structural conformations. Our findings contribute to a deeper understanding of amylose structures and spectroscopic signatures, with implications for theoretical studies and potential applications. This work provides valuable reference points for the detailed assignment of Raman peaks of amylose structure, facilitating their application in broader research on carbohydrate structures and their associated spectroscopic properties.

Quantifying bimolecular reaction kinetics of isoprene hydroxy peroxy radical: From dry to highly humid atmospheric environment

Isoprene hydroxy peroxy radicals (ISOPOO), derived from isoprene oxidation by hydroxy radicals (OH), are key intermediates for ozone and secondary organic aerosol (SOA) formation in the atmosphere. Although ISOPOO-water complexes are ubiquitous, their impacts on ISOPOO chemistry remain obscure. Here the previously overlooked water effect on the bimolecular reaction kinetics of ISOPOO was investigated in an oxidative flow reactor. The major first-generation products of ISOPOO, isoprene hydroxy hydroperoxides (ISOPOOH), methacrolein (MACR), and methyl vinyl ketone (MVK), were measured simultaneously at various relative humidity (RH) with the help of a cold trap to avoid potential losses in direct gas sampling. We found that ISOPOO reactions were accelerated significantly under wet conditions, with a greater enhancement on 1,2-ISOPOO than 4,3-ISOPOO. 1,2-ISOPOOH yield appeared faster growth with RH than 4,3-ISOPOOH. MVK yield showed an upward-downward trend with RH, while MACR yield plateaued from 30% RH. To explain the enhancement in the ISOPOOH yield from 3% to 80% RH, the overall rate constants of 1,2-ISOPOO + HO2 and 4,3-ISOPOO + HO2 reactions at 80% RH should be 13 times and twice those at 3% RH, respectively. The empirical formulas were proposed for the first time to parameterize the water effect on ISOPOO + HO2 reactions. The updated kinetics of ISOPOO reactions were incorporated in a box model to simulate the RH-dependent ISOPOOH and C4 carbonyl yields under typical atmospheric conditions. High RH can enhance the ISOPOOH yield in urban, rural, and forest areas, and promote SOA formation correspondingly. Our findings shed light on the critical role of humidity in the reactions of ISOPOO and benefit evaluating the fate of isoprene and its impacts on air quality more accurately in the ambient atmosphere.

A Quantum Chemical Study on the Bonding Mechanism, Electronic Structure, and Optical Properties of Cellulose and Polyaniline Nanohybrid

A Quantum Chemical Study on the Bonding Mechanism, Electronic Structure, and Optical Properties of Cellulose and Polyaniline Nanohybrid

Disentangling the Conformational Space and Structural Preferences of Tetrahydrofurfuryl Alcohol Using Rotational Spectroscopy and Computational Chemistry.

The influence of the hydroxymethyl (CH2OH) group on the tetrahydrofuran (THF) ring structure was investigated by disentangling the gas phase conformational landscape of the sugar analogue tetrahydrofurfuryl alcohol (THFA). By combining rotational spectroscopy (6-20 GHz) and quantum chemical calculations, transitions corresponding to two stable conformers of THFA and their 13C isotopologues were observed and assigned in the rotational spectrum. The positions of the C atoms were precisely determined to unambiguously distinguish between nearly isoenergetic pairs of conformers that differ in their ring configurations: envelope (E) versus twist (T). The rotational spectrum confirms that the E ring geometry is favoured when the CH2OH fragment lies gauche (-) to the THF backbone (OCCO ~-60°) whereas the T form is more stable for the gauche (+) alignment of the substituent (OCCO ~+60°). The observed spectral intensities suggest that conformational relaxation of the THF geometry (E↔T) to the more stable form readily occurs within the pairs of g- and g+ conformers which is consistent with the low barriers (1.5-1.7 kJ mol-1) for conversion determined via transition state calculations. Insights into the intramolecular hydrogen bonding and other weak interactions stabilizing the lowest energy structures of THFA were derived and rationalized using non-covalent interaction analyses.

Unusual Rearrangements in Cyclohex-3-ene-1-carboxamide Derivatives: Pathway to Bicyclic Lactones.

The synthesis of new bicyclic lactone derivatives was carried out starting from 2-methyl/phenyl-3a,4,7,7a-tetrahydro-1H-isoindole-1,3(2H)-dione. 6-(Hydroxymethyl)-N-methyl/phenylcyclohex-3-ene-1-carboxamide derivatives were obtained from the reduction of tetrahydro-1H-isoindole-1,3(2H)-diones with NaBH4. Bromination and epoxidation reactions of both compounds were examined, and the structures of the resulting products were determined by spectroscopic methods. Substituted bicyclic lactone compounds, which are interesting rearrangement products in both bromination and epoxidation reactions, were obtained. In particular, hydroxymethyl (-CH2OH) and amide (-CONHR) groups attached to the cyclohexene ring in the bromination and epoxidation reactions were found to be effective in product formation. As a result, a new and applicable method was developed for the synthesis of bicyclic lactone derivatives.

Direct and TEMPO‐Mediated Electro‐Oxidation of 5‐(Hydroxymethyl)furfural in Organic and Hydro‐Organic Media

AbstractBiomass‐derived 5‐hydroxymethyl furfural (5‐HMF) is a promising starting substrate for producing two high value‐added products 2,5‐diformylfuran (DFF) and 2,5‐furandicarboxylic acid (FDCA). DFF, which is produced by selectively oxidizing the hydroxymethyl group of 5‐HMF to an aldehyde group, has many applications in pharmaceuticals, macrocyclic ligands and fluorescent materials. Oxidizing both aldehyde and hydroxymethyl groups of 5‐HMF leads to FDCA, which is an important monomer in the production of a bioplastic polyethylene furanoate polymer. Electrochemical conversion of 5‐HMF is a potential route for sustainable chemical production of DFF and FDCA. In fact, using 2,2,6,6‐tetramethyl‐ piperidine‐1‐oxyl (TEMPO) as a redox mediator leads to a highly efficient and selective electro‐oxidation of 5‐HMF into FDCA in a basic buffer solution. In this report, the direct and TEMPO‐mediated electro‐oxidation of 5‐HMF was investigated in various organic and hydro‐organic media at room temperature. Direct electro‐oxidation leads to a low selective conversion of 5‐HMF to DFF (10 % of yield) and the formation of unwanted products such as formic acid and protoanemonin (90 % and 37 % of yield respectively) in acetonitrile. Electrocatalytic 5‐HMF conversion in the presence of TEMPO as a redox mediator achieved a near‐quantitative yield of DFF in acetonitrile and γ‐valerolactone. Importantly, we demonstrate the role of water in the conversion of aldehydes to carboxylic acids.

Effect of drying temperature on the curing properties of phenolic resin-impregnated heat-treated bamboo bundles

ABSTRACT Unreasonable drying temperatures may lead to precuring of phenolic (PF) resin-impregnated heat-treated bamboo bundles before hot-pressing, which is detrimental to the bonding performance of the bamboo scrimber during hot-pressing. In this study, PF resin-impregnated heat-treated bamboo bundles were dried at 50°C, 60°C, and 70°C for 16 h (PHB50, PHB60, and PHB70) and then prepared into bamboo scrimber (BS50, BS60, and BS70) by hot-pressing. The relationship between the curing properties of the PHBwet after drying and the water uptake of BS specimens was analyzed, which showed that the water uptake of BS was inversely proportional to the drying temperature. The curing degrees of the PHB50, PHB60, and PHB70 were 27%, 58%, and 60%, respectively. The water uptake of BS50, BS60, and BS70 after 24 h immersion in room-temperature water was 5%, 11%, and 19%, respectively, resulting in thickness swelling rates of 1%, 2%, and 4%. Compared with BS50, the cross-section of BS70 broke more easily during the cyclic treatment and showed more cracks afterward. The relative contents of C–O bonds and hydroxymethyl groups decreased, indicating that the PHB specimens underwent pre-curing at higher drying temperatures, which inhibited interfacial bonding during hot-pressing.

Properties of soybean oil oleogels produced from sophorolipid‐derived hydroxy fatty acids, methyl esters and hydrogenated Lesquerella seed oil

AbstractSophorolipids (SL) are glycolipids composed of a sophorose head‐group linked to a hydroxy‐fatty acid tail which makes them a potential source of structurally unique biobased hydroxy fatty acids. Furthermore, Lesquerella is a native southwestern plant that has been commercially cultivated as a replacement for castor seed oil due to high seed oil concentrations of 14‐hydroxy‐eicosenoic acid (14‐OH‐C20:1c11). In this study, SL‐derived hydroxy fatty acids and methyl esters containing 15‐hydroxy‐palmitic acid (15‐OH‐C16), 17‐hydroxy‐stearic acid (17‐OH‐C18), 15‐hydroxy‐palmitic acid methyl ester (15‐OH‐C16ME), 17‐hydroxy‐stearic acid methyl ester (17‐OH‐C18ME), and 13‐hydroxy‐behenic acid methyl ester (13OH‐C22ME) were obtained from the SL produced by two yeast strains. In addition, hydrogenated Lesquerella oil (HLO) was made with ~62% 14‐OH‐eicosanoic (C20) acid (14‐OH‐C20). These materials, along with 12‐hydroxy‐stearic acid (12‐OH‐C18) as a standard for comparison were used to make soybean oil oleogels, and their properties determined. The minimum gelation concentration (MGC) of 12‐OH‐C18 was 1% (wt/wt), while the MGC of 15‐OH‐C16 and 17‐OH‐C18 were 5% and 10%, respectively. The MGC for 15‐OH‐C16ME was 5%, but 17‐OH‐C18ME was unable to form a stable gel at concentrations up to 10%. HLO formed a viscous solution rather than an oleogel, but its crystal morphology underwent a large transformation during storage over a 2.5‐month period, after which it was able to form a stable gel. SL‐based hydroxy fatty acids were able to form oleogels in soybean oil and have the potential to be considered as a new source of low‐molecular weight oleogelators as well as biobased hydroxy fatty acids.

Copper‐Catalyzed Formal [4+2] Cycloaddition of Ethynylethylene Carbonates for the Construction of 3,4‐Dihydro‐2H‐benzo[b][1,4]oxazines

A formal [4+2] cycloaddition reaction of ethynylethylene carbonates and 2‐aminophenols has been developed for the synthesis of 3,4‐dihydro‐2H‐benzo[b][1,4]oxazines bearing quaternary carbon atoms. The reaction features mild reaction conditions, good functional group compatibility and good yields. Furthermore, when using chiral PyBox ligand, this strategy could also achieve the asymmetric synthesis of 3,4‐dihydro‐2H‐benzo[b][1,4]oxazines. Application studies indicated that the hydroxymethyl group of final products was an excellent functional group that can be further modified easily.

A highly bioactive THPC-crosslinked recombinant collagen hydrogel implant for aging skin rejuvenation

Skin aging, a complex physiological progression marked by collagen degradation, poses substantial challenges in dermatology. Recombinant collagen emerges as a potential option for skin revitalization, yet its application is constrained by difficulties in forming hydrogels. We have for the first time developed a highly bioactive Tetrakis(hydroxymethyl) phosphonium chloride (THPC)-crosslinked recombinant collagen hydrogel implant for aging skin rejuvenation. THPC demonstrated superior crosslinking efficiency compared to traditional agents such as EDC/NHS and BDDE, achieving complete recombinant collagen crosslinking at minimal concentrations and effectively inducing hydrogel formation. THPC's four reactive hydroxymethyl groups facilitate robust crosslinking with triple helical recombinant collagen, producing hydrogels with enhanced mechanical strength, excellent injectability, increased stability, and greater durability. Moreover, the hydrogel exhibited remarkable biocompatibility and bioactivity, significantly promoting the proliferation, adhesion, and migration of human foreskin fibroblast-1. In photoaged mice skin models, the THPC-crosslinked collagen hydrogel implant notably improved dermal density, skin elasticity, and reduced transepidermal water loss, creating a conducive environment for fibroblast activity and healthy collagen regeneration. Additionally, it elevated superoxide dismutase (SOD) activity and displayed substantial anti-calcification properties. The THPC-crosslinked recombinant collagen hydrogel implant presents an innovative methodology in combating skin aging, offering significant promise in dermatology and tissue engineering.

In vitro demetalation of central magnesium in various chlorophyll derivatives using Mg-dechelatase homolog from the chloroflexi Anaerolineae.

In the metabolic pathway of chlorophylls (Chls), an enzyme called STAY-GREEN or SGR catalyzes the removal of the central magnesium ion of Chls and their derivatives to their corresponding free bases, including pheophytins. The substrate specificity of SGR has been investigated through in vitro reactions using Chl-related molecules. However, information about the biochemical properties and reaction mechanisms of SGR and its substrate specificity remains elusive. In this study, we synthesized various Chl derivatives and investigated their in vitro dechelations using an SGR enzyme. Chl-a derivatives with the C3-vinyl group on the A-ring, which is commonly found as a substituent in natural substrates, and their analogs with ethyl, hydroxymethyl, formyl, and styryl groups at the C3-position were prepared as substrates. In vitro dechelatase reactions of these substrates were performed using an SGR enzyme derived from an Anaerolineae bacterium, allowing us to investigate their specificity. Reactivity was reduced for substrates with an electron-withdrawing formyl or sterically demanding styryl group at the C3-position. Furthermore, the Chl derivative with the C8-styryl group on the B-ring was less reactive for SGR dechelation than the C3-styryl substrate. These results indicate that the SGR enzyme recognizes substituents on the B-ring of substrates more than those on the A-ring.

Electron-rich ruthenium nanoparticles on nitrogen-doped carbon for the efficient catalytic oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid

Modulating the electronic structure of metal nanoparticles (NPs) demonstrates to be useful for the optimization of the catalytic performance. Herein, electron-sufficient ruthenium NPs were successfully constructed on a nitrogen-doped carbon support (Rux-NC), which displayed excellent catalytic activity for the oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA). Especially, a high FDCA yield of 97% was implemented over Ru2.0/NC catalyst in water. The FDCA productivity in this case is also as high as 4.8 molFDCA‧molRu−1‧h−1, which value exceeds most of the previous reported Ru-based catalysts for the production of FDCA. It has been disclosed that the Ru2.0/NC was endowed with high N content and abundant electron-rich Ru0 NPs evoked by the electronic interactions between the NC support the Ru NPs. These facts greatly contribute to the activation of O2, and accelerate the oxidation both of the hydroxymethyl and aldehyde groups of HMF to the carboxyl one. This work provides new understanding for the development of effective Ru-based catalysts for the catalytic oxidation reactions by the electronic structure regulation strategy.

MA'AT Analysis: Unbiased Multi-State Conformational Modeling of Exocyclic Hydroxymethyl Group Conformation in Methyl Aldohexopyranosides.

MA'AT analysis (J. Chem. Inf. Model. 2022, 62, 3135-3141) has been applied to model exocyclic hydroxymethyl group conformation in methyl β-D-glucopyranoside (βGlcOMe), methyl β-D-galactopyranoside (βGalOMe), and methyl β-D-mannopyranoside (βManOMe) in an unbiased manner. Using up to eight NMR J-couplings sensitive to rotation about the C5-C6 bond (torsion angle ω), two-state models of ω were obtained that are qualitatively consistent with the relative populations of the gg, gt, and tg rotamers reported previously. MA'AT analysis gave consistent unbiased gt ⇌ tg models of ω in βGalOMe, with gt more populated than tg and mean values of ω for each population similar to those obtained from aqueous 1-μs MD simulation. Using different combinations of J-couplings had little effect on the βGalOMe model in terms of the mean values of ω and circular standard deviations (CSDs). In contrast, MA'AT analysis of ω in βGlcOMe and βManOMe produced more than one two-state model independent of the ensemble of J-values used in the analyses. These models were characterized by gg ⇌ gt conformer exchange as expected, but the mean values of ω in both conformers varied significantly in the different fits, especially for the gg rotamer. Constrained (biased) MA'AT analyses in which only staggered geometries about ω were allowed gave RMSDs slightly larger than those obtained from the unbiased fits, precluding an assignment of an unbiased model. It is unclear why MA'AT analysis gives consistent and predictable unbiased models of ω in βGalOMe but not in βGlcOMe and βManOMe. One possibility is that the distribution of ω in one or both of the gg and gt conformers in the latter does not conform to a von Mises function (i.e., is not Gaussian-like), but rather to a broad and/or flat distribution that cannot be fit by the current version of MA'AT. Nevertheless, the results of this study provide new evidence of the ability of MA'AT analysis to treat multi-state conformational exchange using only experimental NMR data, extending recent MA'AT applications to furanosyl ring pseudorotation (Biochemistry 2022, 61, 239-251).

In vitro and In silico Evaluation of Antibacterial Effects in Some Oxadiazole Compounds against Escherichia coli O157: H7

Background: Escherichia coli O157:H7 is a significant pathogen responsible for causing diarrhea in humans. Oxadiazoles are known for their diverse range of biological activities. Objectives: This study aimed to assess the anti-E. coli O157:H7 effects of 1, 3, and 4-oxadiazole derivatives. Methods: Compounds containing an oxadiazole central core were synthesized anew. In vitro assays, including agar well diffusion, minimum inhibitory concentration, and minimum bactericidal concentration, were conducted. The molecular structures of the oxadiazole derivatives were optimized using the mm2 methodology with Chem3D v20.1.1.125 software. The ligand's inhibitory potential against the active sites of stx-1 and stx-2 was assessed using Autodock Vina software. The results were analyzed using Discovery Studio v16.1.0 software. Results: The findings indicated that compound C ((2E)-3-(3,4-difluorophenyl)-2-(5-(hydroxy(pyridin-2-yl)meth yl)-1,3,4-oxadiazol-2-yl)-N-methylacrylimidic acid) exhibited more potent anti-E. coli O157:H7 effects compared to other compounds and the control sample. Furthermore, in silico results demonstrated that compound C exhibited inhibitory effects against stx-1 and stx-2 by forming hydrogen bonds for inhibition. Conclusions: Compounds featuring a fluorophenyl structure with a 1, 3, and 4-oxadiazole core have the potential to serve as anti-E. coli O157:H7 agents for the development of therapeutic drugs.

Research progress of Co and Mn‐based catalysts for the oxidation of 5‐hydroxymethylfurfural

AbstractBiomass is a renewable energy source abundantly available in nature. Their degradation by chemical or biological means produces various transition compounds. These transition compounds can be further transformed into valuable chemicals and biofuels that exhibit a wide range of applications and benefits. Recently, there has been a significant focus on this research area. Among the transition compounds, 5‐hydroxymethylfurfural (HMF), derived from the degradation of hexose, is an important biomass‐based platform compound that has hydroxymethyl and aldehyde functional groups in its molecular structure. This study reviews the recent progress in the transition metal‐catalysed conversion of HMF using Co and Mn to generate high‐value‐added downstream products. Furthermore, the active components, the carbon supporter, the reaction mechanism, the oxidants and the reaction conditions of the catalysts are discussed in detail. The oxidation of HMF deserves further research as an important and complete value‐added process for generating biomass‐based valuable chemicals.

Modulation of hydroxymethyl/aldehyde groups activation on V2O3 decorated CuCo for 5-hydroxymethylfurfural electrooxidation

5-Hydroxymethylfurfural electrooxidation reaction (HMFOR) has attracted increasing attention due to energy conservation and value-added production. It is crucial to design highly active catalysts with fast kinetics and reveal the catalytic mechanism. Herein, the activation of hydroxymethyl/aldehyde groups is tuned on V2O3-modificated CuCo for efficient HMFOR. Experimental and theoretical results reveal that strong electron transfer occurs on the heterointerface between V2O3 and CuCo, endowing its unique electronic structure and conductivity. Meanwhile, CuCo-V2O3 heterostructure facilitates the modulation of local electron density, charge transfer, and adsorption behavior to promote the activation of hydroxymethyl/aldehyde groups. The higher activation of hydroxymethyl groups than that of aldehyde groups over CuCo-V2O3 induces an altered rate-determining step for HMFOR. Consequently, CuCo-V2O3 presents enhanced HMFOR activity (E10, 1.27 VRHE), reaction kinetics (38 mV dec−1), 2,5-furandicarboxylic acid selectivity (99.1%), and stability (40 successive cycles). This work provides a strategy for designing highly active catalysts for synthesizing value-added products.

A Protection Strategy for High‐yield Synthesis of Dimethyl Furan‐2,5‐dicarboxylate from 5‐Hydroxymethylfurfural Using Methanol as an Acetalizing Agent

AbstractDeveloping efficient catalytic processes for obtaining biobased monomers for plastics can significantly contribute to a more sustainable economy. The biomass‐derived and chemical platform 5‐hydroxymethylfurfural (HMF) can be converted to various key intermediates, which is often hampered by side reactions due to the reactive nature of the formyl group in HMF. Here, we present a stepwise approach involving a protecting agent to obtain dimethyl furan‐2,5‐dicarboxylate (MFDC), which is a monomer for polyalkylene furanoates, a new class of biobased polyesters. Methanol is used as a solvent, reactant, and protecting agent for HMF's formyl group. In the first step, the oxidative esterification of the hydroxymethyl group to methyl carboxylate in HMF‐dimethylacetal catalyzed by Au/CeO2 affords methyl 5‐formylfuran‐2‐carboxylate dimethylacetal (MFFC‐acetal) in high yields (>90 %) from concentrated methanolic solutions (~20 wt %). Without protecting agent, a mixture of methyl‐5‐hydroxymethylfuran‐2‐carboxylate (MHMFC), MFDC, and humin byproduct was obtained. The deprotection of MFFC‐acetal in the second step proceeded efficiently in acetone with Amberlyst‐15, affording MFFC in a >90 % yield. In the final step, oxidative esterification of MFFC in methanol (10 wt %) afforded MFDC in a 93 % yield using Au/CeO2. The acetal protection strategy with methanol offers an efficient route toward MFDC in two oxidative esterification steps.

Antioxidant and Antibacterial Activity of Endophytic Fungi Isolated from Fruit of Sungkai (Peronema canescens)

Peronema canescens, often known as sungkai, is widely used and can be found all around Indonesia. The public believes that the leaves may reduce fever and strengthen the immune system. However, the effectiveness of sungkai fruit has not been thoroughly investigated. In this research, we looked at endophytic fungus extracts from sungkai fruit’s that have antioxidant and antibacterial properties. The study’s results will serve as the foundation for further investigation into the development of potential natural chemicals with antioxidant and antibacterial properties. Morphologically, the endophytic fungi isolated from sungkai fruit were identified. The antioxidant and antibacterial properties of endophytic fungal extracts were studied using the DPPH technique and the paper disk diffusion method. By employing molecular identification and column chromatography to separate the active compounds, the most likely endophytic fungal isolates were found based on the results of the bioactivity tests. Using 1D NMR spectroscopic methods, the chemical’s structure was determined, and the results were compared to NMR data for the same compound published in the literature. Fruit of sungkai had 8 strains of endophytic fungus (RBH1-RBH8). Strong antibacterial and very strong antioxidant activity were shown by the RBH5 isolate (IC50 < 20 μg/mL). Pythium periplocum was determined to be the RBH5 isolate based on molecular testing. Pure chemical compound extracted from RBH5 isolates shown highly potent and potent antibacterial and antioxidant effects. The chemical compound was identified by spectroscopy as 3-hydroxy-4(hydroxy(4-hydroxyphenyl)methyl)-γ-butyrolactone. The results of this study serve as the foundation for developing compounds as pharmaceutical raw materials via further research phases.

Novel Dihydrocoumarins Induced by Radiolysis as Potent Tyrosinase Inhibitors.

A representative naturally occurring coumarin, 4-methylumbelliferone (5), was exposed to 50 kGy of gamma ray, resulting in four newly generated dihydrocoumarin products 1-4 induced by the gamma irradiation. The structures of these new products were elucidated by interpretation of spectroscopic data (NMR, MS, [α]D, and UV). The unusual bisdihydrocoumarin 4 exhibited improved tyrosinase inhibitory capacity toward mushroom tyrosinase with IC50 values of 19.8 ± 0.5 μM as compared to the original 4-methylumbelliferone (5). A kinetic analysis also exhibited that the potent metabolite 4 had non-competitive modes of action. Linkage of the hydroxymethyl group in the C-3 and C-4 positions on the lactone ring probably enhances the tyrosinase inhibitory effect of 4-methylumbelliferone (5). Thus, the novel coumarin analog 4 is an interesting new class of tyrosinase inhibitory candidates that requires further examination.

Syntheses and exploration of the catalytic activities of organotin(IV) compounds.

Six organotin(IV) compounds (1-6) have been synthesized by reaction of the polydentate pro-ligands H3L and H2L, respectively, with the corresponding diorganotin chlorides. All of the compounds were characterized by FT-IR spectroscopy, 1H, 13C{1H}, and 119Sn (1H) NMR spectroscopy, HRMS spectrometry, and single-crystal X-ray diffraction. The solid-state structures show that all of the compounds are monomeric (except compound 3) and contain a penta-coordinated tin atom. Compound 3 is a dimer with two hexa-coordinated tin atoms. Compounds 1-3 contain a non-coordinated hydroxymethyl group. All of the compounds have been screened for their catalytic efficacy in the synthesis of 1,2 disubstituted benzimidazoles using o-phenylenediamine and aldehyde derivatives. It has been observed that both the Lewis acidic Sn(IV) centre and the hydroxymethyl group (hydrogen bond donor) catalyse the reactions with a product yield of up to 92%.