Alkali metal cations can inhibit non-covalent catalysis

The study concerns the effect of inorganic salts on supramolecular catalysis. The model reaction is the acid hydrolysis of the ammonium phenyl acetate derivative promoted by cucurbit[7]uril macrocycle. When salt is absent, the macrocycle is insensitive to the ionic strength of the solution, and the reaction rate linearly depends on the concentration of hydronium ions (H3O+). After the addition of inorganic salts, in particular, Na+ and K+ ions, the catalytic effect of the macrocycle is suppressed. The kinetic and binding data collected by us evidence the formation of the ternary complexes between the cations, macrocycle, and substrate, which are less prone to H3O+ attack. This type of inhibition corresponds to a rare uncompetitive model in contrast to a more common competitive one that relies on the displacement of the substrate. This study shows that special care must be taken when studying catalysis in solutions that contain metal cations, such as regular water and inorganic buffers.

Cytotoxic and antibacterial properties of resveratrol oligomers from the stem bark of Dryobalanops rappa

Background: Dryobalanops rappa is a Plant species belong to the family of Dipterocarpaceae. Nevertheless, the active compounds present in D. rappa have never been investigated. Objective: The aim of this research is to isolate and characterize compounds from Dryobalanops rappa and to study its bioactivity against human MCF-7 breast cancer and A549 lung cancer cell lines and several bacterial strains. Methods: The isolation step was carried out using a combination of chromatographic techniques. The structure of the isolated compounds was elucidated mainly using NMR spectroscopy. The cytotoxic activity of isolated compounds was determined with MTT assay, and the antimicrobial was screened using a modified resazurin microtiter-plate assay. Results: Isolation and purification of methanolic extract of D. rappa stem bark yielded 14 known oligomeric resveratrol types of compounds (1-14). Results showed that isolated ampelopsin E (5) and vaticanol C (14) displayed moderate activity against human MCF-7 breast cancer and A549 lung cancer cell lines with IC50 values 14.3 and 10.7 μg/mL, respectively. Interestingly, acetate derivative of isolated laevifonol (2) and ampelopsin F (3) possess potent activities towards MCF-7 cancer cell line with IC50 values 2.8 and 3.3 μg/mL, respectively, in comparison to the parental compounds that demonstrated weak activities (IC50 > 50 μg/mL). For the antibacterial assay, compounds 10 and 12 showed moderate activities towards Gram-positive bacterial strains (MIC ≤ 50 μM). Conclusion: 14 known oligomeric resveratrol types of compounds have been isolated. The good activity of 14 against A549 cell line, 5 against MCF-7 cell line, and 10 and 12 against Gram-positive bacterial strains were the most promising results from this study. While the strong cytotoxicity of acetate derivative (2 and 3) against MCF-7 cell line has opened up the potential of resveratrol oligomers to be used as a template for designing new anticancer drugs.

Acaricidal activity of essential oils of Cinnamomum zeylanicum and Eremanthus erythropappus, major compounds and cinnamyl acetate in Rhipicephalus microplus

This study aimed to chemically characterize the essential oils (EOs) of Cinnamomum zeylanicum (cinnamon) and Eremanthus erythropappus (candeia) and evaluate their acaricidal activity, together with that of their major compounds and cinnamyl acetate derivative, against Rhipicephalus microplus. Essential oil compounds were identified through gas chromatography. The larval packet test (LPT) at concentrations ranging from 0.31 to 10.0 mg/mL and the adult immersion test (AIT) at concentrations between 2.5 and 60.0 mg/mL were performed. (E)-cinnamaldehyde and α-bisabolol were the major compounds in cinnamon (86.93%) and candeia (78.41%) EOs, respectively. In the LPT, the EOs of cinnamon and candeia and the compounds (E)-cinnamaldehyde, α-bisabolol and cinnamyl acetate resulted in 100% mortality at concentrations of 2.5, 2.5, 5.0, 10.0 and 10.0 mg/mL respectively. In the AIT, percentage control values > 95% were observed for cinnamon and candeia EOs, (E)-cinnamaldehyde and α-bisabolol at the concentrations of 5.0, 60.0, 20.0, and 20.0 mg/mL, respectively, whereas cinnamyl acetate showed low activity. We conclude that EOs and their compounds showed high acaricidal activity, whereas the acetylated derivative of (E)-cinnamaldehyde presented less acaricidal activity on R. microplus engorged females.

Unnatural Amino Acid Derivatives through Click Chemistry: Synthesis of Triazolylalanine Analogues

A novel tert-butyl 2-(1-oxoisoindolin-2-yl)acetate derivative is selectively alkylated with propargyl bromide in the presence of lithium hexamethyldisilazide. After removal of the tert-butyl protecting group, the resulting N-isoindolinyl (ethynylalanine) derivative is reacted with a series of azides under ‘click conditions’. The click reactions afford an array of N-isoindolinyl- 1,2,3-triazolylalanine derivatives as the free carboxylic acids. Following esterification, the N-isoindolinone protecting group is then transformed into the more easily removable phthaloyl group by selective oxidation at the benzylic position.

Enzyme-catalyzed kinetic resolution of N-Boc-trans-3-hydroxy-4-phenylpyrrolidine

The first enzyme-catalyzed kinetic resolution of tert-butyl-3-hydroxy-4-phenylpyrrolidine-1-carboxylate is presented. Enzyme, solvent and temperature optimization resulted in a new resolution method with E = 40 enantioselectivity. The acetate derivative of the (+)-(3S,4R) enantiomer formed while the (−)-(3R,4S) isomer remained intact. Very good enantioselectivities (E > 200) were achieved in the enzyme-catalyzed alcoholysis of the racemic acetate in i-propanol and t-butanol where the (+)-(3S,4R) enantiomer was prepared in pure form (ee > 99.7%). Absolute configuration of the (−)-(3R,4S)-enantiomer was determined by single crystal X-ray diffraction method.

Investigation on Orange Peel: Derivatization of Isolated Cellulosic Material and Analysis of the Fatty Acids Composition

Isolation of cellulosic material from the waste material, orange (Citrus sinensis) peel has been carried out. The isolated cellulosic material has been converted into its acetate ester. The acetate derivative has been characterized by titrimetric method and IR spectra. The fatty acid composition of the orange peel has also analyzed by GLC. Successful conversion of agro-waste into its acetate derivative and the fatty acid composition suggest an alternative use of this waste material.DOI: http://dx.doi.org/10.3329/dujs.v60i1.10341 Dhaka Univ. J. Sci. 60(1): 77-78 2012 (January)