35 research outputs found
Elucidating the Sugar Tailoring Steps in the Cytorhodin Biosynthetic Pathway
Anthracycline antitumor
cytorhodins X and Y feature a rare 9α-glycoside
and 7-dexoy-aglycone. Characterization of the cytorhodin gene cluster
from <i>Streptomyces</i> sp. SCSIO 1666 through gene inactivations
and metabolite analyses reveals three glycosyltransferases (GTs) involved
in the sugar tailoring steps. The duo of CytG1 and CytL effects C-7
glycosylation with l-rhodosamine whereas the iterative GT
CytG3 and CytW similarly modifies both C-9 and C-10 positions. CytG2
also acts iteratively by incorporating the second and third sugar
moiety into the trisaccharide chains at the C-7 or C-10 position
A Trifluoromethylcarbene Source
The trifluoromethylcarbene (:CHCF<sub>3</sub>) was found to be
conveniently generated from (2,2,2-trifluoroÂethyl)Âdiphenyl-sulfonium
triflate (Ph<sub>2</sub>S<sup>+</sup>CH<sub>2</sub>CF<sub>3</sub> <sup>–</sup>OTf), which was successfully applied in Fe-catalyzed
cyclopropanation of olefins, giving the corresponding trifluoromethylated
cyclopropanes in high yields
Cytotoxic and Anti-inflammatory Triterpenoids from <i>Toona ciliata</i>
Toonaciliatavarins A–H (<b>1</b>–<b>8</b>), including three new protolimonoids (<b>1</b>–<b>3</b>), two new tirucallane-type triterpenoids (<b>4</b> and <b>5</b>), and three new tetranortriterpenoids (<b>6</b>–<b>8</b>), and 10 known compounds were isolated
from the stem barks of <i>Toona ciliata Roem.</i> var. <i>henryi</i>. Their structures were identified on the basis of
spectroscopic analysis. The absolute configurations of <b>2</b> and <b>8</b> were determined by ECD calculation. The new isolates
were evaluated for their cytotoxicities using six human cancer cell
lines and also for their inhibitory effects on lipopolysaccharide-induced
nitric oxide production in RAW264.7 cells. Compounds <b>4</b> and <b>5</b> showed moderate cytotoxicities, and the protolimonoids
(<b>1</b>–<b>3</b>) exhibited marked inhibitory
effects on LPS-stimulated NO production
Penimethavone A, a flavone from a gorgonian-derived fungus <i>Penicillium chrysogenum</i>
<p>A novel flavone, penimethavone A (<b>1</b>), possessing a rare unique methyl group at ring-B, was isolated from the fungus <i>Penicillium chrysogenum</i> cultured from a gorgonian <i>Carijoa</i> sp. collected from the South China Sea. The structure was elucidated by extensive spectroscopic analysis and by comparison with related known compound. Compound <b>1</b> showed selective and moderate cytotoxicity against cervical cancer (HeLa) and rhabdomyosarcoma cell lines with IC<sub>50</sub> values of 8.41 and 8.18 μM, respectively.</p
Organocatalyzed Michael–Michael Cascade Reaction: Asymmetric Synthesis of Polysubstituted Chromans
An
enantioselective cascade Michael–Michael reaction between
chalcones enolates and nitromethane catalyzed by a bifunctional thiourea
is developed. This reaction provides a mild but efficient approach
to chiral benzopyrans bearing three consecutive stereocenters in high
yields with excellent stereoselectivities, and the benzopyrans can
be easily transformed to the corresponding tricyclic product
Organocatalyzed Michael–Michael Cascade Reaction: Asymmetric Synthesis of Polysubstituted Chromans
An
enantioselective cascade Michael–Michael reaction between
chalcones enolates and nitromethane catalyzed by a bifunctional thiourea
is developed. This reaction provides a mild but efficient approach
to chiral benzopyrans bearing three consecutive stereocenters in high
yields with excellent stereoselectivities, and the benzopyrans can
be easily transformed to the corresponding tricyclic product
Organocatalytic, Enantioselective Friedel–Crafts Reaction of Indoles in the Carbocyclic Ring and Electron-Rich Phenols
An
efficient method has been successfully developed to achieve
the asymmetric C–H functionalization of indoles in the carbocyclic
ring via organocatalysis, and a variety of tetrahydropyranoindoles
were synthesized in good yields with excellent stereoselectivities.
Further study on thermodynamic calculations indicated that the process
was promoted by generating more thermodynamically stable products.
This strategy, together with traditional C-3 functionalization of
hydroxyindoles, could realize the switchable, regiodivergent asymmetric
modification of indoles
Cu-Catalyzed C–H Trifluoromethylation of 3‑Arylprop-1-ynes for the Selective Construction of Allenic Csp<sup>2</sup>–CF<sub>3</sub> and Propargyl Csp<sup>3</sup>–CF<sub>3</sub> Bonds
A new
method has been developed for the Cu-catalyzed C–H
trifluoromethylation of 3-arylprop-1-ynes for the selective construction
of allenic Csp<sup>2</sup>–CF<sub>3</sub> and propargyl Csp<sup>3</sup>–CF<sub>3</sub> bonds. The selective formation of allenic
Csp<sup>2</sup>–CF<sub>3</sub> and propargyl Csp<sup>3</sup>–CF<sub>3</sub> bonds can be controlled by modifying the reaction
conditions
Bioactive Terpenoids from the Fruits of <i>Aphanamixis grandifolia</i>
From the fruits of the tropical tree <i>Aphanamixis grandifolia</i>, five new evodulone-type limonoids,
aphanalides I–M (<b>1</b>–<b>5</b>), one
new <i>apo</i>-tirucallane-type
triterpenoid, polystanin E (<b>6</b>), and three new chain-like
diterpenoids, nemoralisins A–C (<b>7</b>–<b>9</b>), along with 12 known compounds were identified. The absolute
configurations were determined by a combination of single-crystal
X-ray diffraction studies, Mo<sub>2</sub>(OAc)<sub>4</sub>-induced
electronic circular dichroism (ECD) data, the Mosher ester method,
and calculated ECD data.
The cytotoxicities of all the isolates and the insecticidal activities
of the limonoids were evaluated
Bioactive Terpenoids from the Fruits of <i>Aphanamixis grandifolia</i>
From the fruits of the tropical tree <i>Aphanamixis grandifolia</i>, five new evodulone-type limonoids,
aphanalides I–M (<b>1</b>–<b>5</b>), one
new <i>apo</i>-tirucallane-type
triterpenoid, polystanin E (<b>6</b>), and three new chain-like
diterpenoids, nemoralisins A–C (<b>7</b>–<b>9</b>), along with 12 known compounds were identified. The absolute
configurations were determined by a combination of single-crystal
X-ray diffraction studies, Mo<sub>2</sub>(OAc)<sub>4</sub>-induced
electronic circular dichroism (ECD) data, the Mosher ester method,
and calculated ECD data.
The cytotoxicities of all the isolates and the insecticidal activities
of the limonoids were evaluated