Organocatalytic stereoselective cyanosilylation of small ketones

Enzymatic stereoselectivity has typically been unrivalled by most chemical catalysts, especially in the conversion of small substrates. According to the ‘lock-and-key theory’^1,2, enzymes have confined active sites to accommodate their specific reacting substrates, a feature that is typically absent from chemical catalysts. An interesting case in this context is the formation of cyanohydrins from ketones and HCN, as this reaction can be catalysed by various classes of catalysts, including biological, inorganic and organic ones^3–7. We now report the development of broadly applicable confined organocatalysts for the highly enantioselective cyanosilylation of aromatic and aliphatic ketones, including the challenging 2-butanone. The selectivity (98:2 enantiomeric ratio (e.r.)) obtained towards its pharmaceutically relevant product is unmatched by any other catalyst class, including engineered biocatalysts. Our results indicate that confined chemical catalysts can be designed that are as selective as enzymes in converting small, unbiased substrates, while still providing a broad scope.

The development of confined organocatalysts for the enantioselective cyanosilylation of small, unbiased substrates, including 2-butanone, is shown to lead to catalysts that are as selective as enzymes, with excellent levels of control.

Abietane Diterpenoids from the Roots of Clerodendrum trichotomum and Their Nitric Oxide Inhibitory Activities

Twelve new abietane diterpenoids (1-12) and 31 known analogues (13-43) were isolated from a medicinal Chinese herb, Clerodendrum trichotomum Thunberg. The absolute configurations of 1-3 were established on the basis of ECD and X-ray crystallography data, whereas that of 4 was elucidated by comparison of experimental and calculated ECD data. Eight diterpenoids, 15,16-dehydroteuvincenone G (1), trichotomin A (4), 2α-hydrocaryopincaolide F (7), villosin C (20), 15-dehydro-17-hydroxycyrtophyllone A (22), demethylcryptojaponol (38), 6β-hydroxydemethylcryptojaponol (39), and trichotomone (43), exerted inhibitory effects against NO production with IC₅₀ values of 5.6-16.1 μM. The structure-activity relationships of the isolated diterpenoids are also estimated.

Scientific validation of medicinal plants used by Yakkha community of Chanuwa VDC, Dhankuta, Nepal

Ethnobotanical knowledge is important among tribal people, but much of the information is empirical due to the lack of scientific validation. The purpose of this study was to document the medicinal plants used by an ethnic group (Yakkha) at Chanuwa VDC of Dhankuta district in Nepal and to validate scientifically in the use of plants based on results of phytochemical, antimicrobial and antioxidant property analyses and available literature reports. Data were collected through interviews of the Yakkha people with the help of a semi-structured questionnaire and the guided field walk method. A total of 30 different medicinal plants were recorded along with their vernacular names (for few plants) used by the Yakkha community’s people. Literature review reveals that most of the plant species described herein have also been used in other countries, too. Among 30 plants selected for this study methanol extract of five ethno-medicinal plants viz., Dendrocnide sinuata, Solanum anguivi, Pogostemon cablin, Boehmeria platyphylla and Clerodendrum trichotomum and ethanol extract of C. trichotomum were subjected for antibacterial and antioxidant properties. The antimicrobial activities were measured using the paper disc diffusion method. The antioxidant properties of plants were measured by DPPH and FRAP reduction assay. Among all extracts, ethanol extract of C. trichotomum and methanol extract of B. platyphylla displayed the highest antibacterial and antioxidant activities, respectively.

A new diterpenoid from the leaves of Clerodendron trichotomum

A new diterpenoid was isolated from the leaves of Clerodendron trichotomumThunb. (Verbenaceae) along with one each of a known diterpenoid, phenylethanoid glycoside, and sterol and two known flavonoids. Their chemical structures were characterized on the basis of spectroscopic data and X-ray analysis. In addition, their antioxidant activities were evaluated using four different analyses.

Trichotomoside: A New Antioxidative Phenylpropanoid Glycoside fromClerodendron trichotomum

The structure and antioxidant properties of a new natural glycoside, trichotomoside (1), isolated from Clerodendron trichotomum, were investigated. Trichotomoside was identified as 2-(3-hydroxy-4-methoxyphenyl)ethyl 3-O-(2,3-di-O-acetyl-alpha-L-rhamnopyranosyl)-4-O-[(2E)-3-(3-hydroxy-4-methoxyphenyl)prop-2-enoyl]-beta-D-glucopyranoside. The compound was active towards intracellular reactive oxygen species (ROS) and exhibited DPPH-radical-scavenging effects. The radical-scavenging activity of 1 was found to protect the viability of Chinese hamster lung fibroblasts (V79-4 cells) exposed to H2O2 and gamma-irradiation.

Antioxidant activity of isoacteoside from Clerodendron trichotomum

The antioxidant properties of isoacteoside, isolated from Clerodendron trichotomum (Verbenaceae), were investigated. This compound scavenged intracellular reactive oxygen species (ROS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, and prevented lipid peroxidation. This radical scavenging activity of isoacteoside protected cell viability of Chinese hamster lung fibroblast (V79-4) cells exposed to hydrogen peroxide (H2O2). Furthermore, isoacteoside reduced the apoptotic cells formation induced by H2O2, as demonstrated by the decreased number of sub-G1 hypo-diploid cells and apoptotic cell body formation. However, isoacteoside increased the activities of cellular antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT). Taken together, these findings suggest that isoacteoside, isolated from C. trichotomum, possesses antioxidant properties.

Angiotensin converting enzyme inhibitory phenylpropanoid glycosides from Clerodendron trichotomum

The stems of Clerodendron trichotomum have been traditionally used for treatment of hypertension in far East Asia including China, Korea, and Japan. Bioassay-guided fractionation and purification of the EtOAc-soluble extract of Clerodendron trichotomum afforded acteoside (1), leucosceptoside A (2), martynoside (3), acteoside isomer (4), and isomartynoside (5). The angiotensin converting enzyme (ACE) activities were significantly inhibited by the addition of these phenylpropanoid glycosides (1-5) in a dose-dependent manner of which IC(50) values were 373+/-9.3 microg/ml, 423+/-18.8 microg/ml, 524+/-28.1 microg/ml, 376+/-15.6 microg/ml, 505+/-26.7 microg/ml, respectively. These results suggest that the antihypertensive effect of Clerodendron trichotomum may be, at least in part, due to ACE inhibitory effect of phenylpropanoid glycosides.

HIV-1 integrase inhibitory phenylpropanoid glycosides from Clerodendron trichotomum

Seven phenylpropanoid glycosides named acteoside (1), acteoside isomer (2), leucosceptoside A (3), plantainoside C (4), jionoside D (5), martynoside (6), and isomartynoside (7) were isolated from Clerodendron trichotomum. Compounds 1 and 2 showed potent inhibitory activities against HIV-1 integrase with IC50 values of 7.8 +/- 3.6 and 13.7 +/- 6.0 microM, respectively.