Samran Prabpai

Fluoride-Catalyzed Addition of PhSCF2SiMe3 to N-Substituted Cyclic Imides Followed by Radical Cyclization: General Synthetic Strategy of gem-Difluoromethylenated 1-Azabicyclic Compounds

PhSCF(2)SiMe(3) (1) was found, for the first time, to undergo fluoride-catalyzed nucleophilic difluoro(phenylsulfanyl)methylation reaction to cyclic imides 2, affording the corresponding adducts 3 in moderate to good yields. Reductive cleavage of the phenylsulfanyl group of N-alkylated adducts 3 with Bu(3)SnH/AIBN yielded gem-difluoromethylated products 4. Under the same reduction conditions, N-alkenylated and N-alkynylated adducts 3 afforded the corresponding gem-difluoromethylenated 1-azabicyclic compounds 5 and 6 with trans stereoselectivity. These compounds were employed as precursors for preparing substituted gem-difluoromethylenated pyrrolizidinones and indolizidinones 7 and 8 by treatment with Et(3)SiH/BF(3) x OEt(2), and compounds 9 and 10 by nucleophilic displacement of the hydroxyl group, using organosilanes in the presence of BF(3) x OEt(2). The synthesis of highly substituted gem-difluoromethylenated pyrrolizidines 13 and 14 was also demonstrated.

Cytotoxic pentacyclic and tetracyclic aromatic sesquiterpenes from Phomopsis archeri.

Three new sesquiterpenes, named phomoarcherins A-C (1-3), and four known compounds, kampanol A (4), R-mevalonolactone, ergosterol, and ergosterol peroxide, were isolated from the endophytic fungus Phomopsis archeri. These structures were established on the basis of spectroscopic evidence. The structure and absolute configuration of 1 were confirmed by X-ray crystallographic analysis of its p-bromobenzoate derivative (1a). Compounds 1-4 showed cytotoxicity against five cholangiocarcinoma cell lines (0.1-19.6 μg/mL), while 1 and 2 exhibited weak cytotoxicity against the KB cell line with IC(50) values of 42.1 and 9.4 μg/mL, respectively. In addition, compound 2 showed antimalarial activity against Plasmodium falciparum with an IC(50) value of 0.79 μg/mL.

Dichapetalin-type triterpenoids and lignans from the aerial parts of Phyllanthus acutissima

Chemical investigation of the aerial parts of Phyllanthus acutissima resulted in the isolation of five new dichapetalin-type triterpenoids, acutissimatriterpenes A-E ( 1- 5), and two new lignans, acutissimalignans A ( 6) and B ( 7), along with two known lignans and three known ellagic acid derivatives. The structures of 1- 7 were determined mainly on the basis of spectroscopic methods. The compounds obtained were evaluated for cytotoxic and anti-HIV-1 activities.

Diterpenes, Sesquiterpenes, and a Sesquiterpene−Coumarin Conjugate from Jatropha integerrima

Five new compounds, 2alpha-hydroxyjatropholone (1), 2beta-hydroxyjatropholone (2), 1,5-dioxo-2,3-dihydroxyrhamnofola-4(10),6,11(18),15-tetraene (3), 2-keto-5-hydroxyguai-3,11-diene (4), and a sesquiterpene-coumarin conjugate, jatrophadioxan (5), and nine known compounds have been isolated from the roots of Jatropha integerrima. The structures were established from spectroscopic data, and the relative configuration of 1 was confirmed by X-ray crystallography. Six diterpenes were evaluated for their antiplasmodial, antituberculosis, and cytotoxic activities.

A novel 8,9-seco-rhamnofolane and a new rhamnofolane endoperoxide from Jatropha integerrima roots

Abstract Integerrimene, a possible biogenetic precusor of the rhamnofolane diterpenes and a new rhamnofolane endoperoxide 2-epicaniojane together with caniojane and 1,11-bisepicaniojane were isolated from J. integerrima roots. Their structures were elucidated by spectroscopic methods. The X-ray structure of 2-epicaniojane is also presented.

Synthesis of gem-Difluoromethylenated Bicyclo[m.n.0]alkan-1-ols and Their Ring-Expansion to gem-Difluoromethylenated Macrocyclic Lactones

Fluoride-catalyzed stereoselective nucleophilic addition of PhSCF(2)SiMe(3) (1) to α-carboethoxycycloalkanones 2 followed by intramolecular radical cyclization of the resulting cis-3 adduct afforded the corresponding gem-difluoromethylenated bicyclic compounds 4, which underwent ring-expansion followed by the Baeyer-Villiger-type oxidation of the resulting macrocyclic ketone intermediates to give gem-difluoromethylenated macrocyclic lactones 5.

Asymmetric Synthesis of gem-Difluoromethylenated Dihydroxypyrrolizidines and Indolizidines

An asymmetric synthesis of gem-difluoromethylenated dihydroxypyrrolizidines and indolizidines is described. The fluoride-catalyzed nucleophilic addition of PhSCF(2)SiMe(3) (1) to chiral imides was achieved in satisfactory yields to provide mixtures of syn- and anti-isomers 6-9 with moderate to good diastereoselectivities. Reductive cleavage of the phenylsulfanyl group followed by intramolecular radical cyclization of the syn-isomers 6-9 occurred under refluxing conditions to afford the corresponding gem-difluoromethylenated 1-azabicyclic compounds 10-13 in moderate yields as a separable mixture of cis- and trans-isomers. The cis-isomers of compounds 10 and 12 and trans-13 were readily transformed to gem-difluoromethylenated dihydroxypyrrolizidines 20 and 27 and indolizidine 28, respectively, by reductive cleavage of the hydroxyl group and organometallic addition followed by hydrogenolysis.

Anti-HIV-1 and Anti-Inflammatory Lupanes from the Leaves, Twigs, and Resin of Garcinia hanburyi

Two new lupanes, 2 alpha-acetoxy-3 beta-hydroxy-19 beta-hydrogen-lup-20(29)-en-28-oic acid (2-acetoxyalphitolic acid) ( 1) and 2 alpha-hydroxy-3 beta-acetoxy-19 beta-hydrogen-lup-20(29)-en-28-oic acid (3-acetoxyalphitolic acid) ( 2), together with the known betulinic acid ( 3), betulin ( 4), and stimasterol-3- O- beta- D-glucopyranoside ( 5), were isolated from the leaves and twigs of GARCINIA HANBURYI. Compounds 1- 3 were also isolated from the resin of this plant. The structure of 2 was confirmed by single-crystal X-ray diffraction analysis. All of the lupanes ( 1- 4) displayed anti-HIV-1 activities in the anti-HIV-1 reverse transcriptase (IC (50) values 16.3-116.9 microg/mL) and syncytium assays (EC (50) 5.6-73.6 microg/mL, SI 1.7-3.3). Moreover compounds 1- 4 exhibited anti-inflammatory activity in an ethyl phenylpropiolate (EPP)-induced ear edema model.

Trishomocubane Amino Acid as a β‐turn scaffold

The synthesis and X‐ray structure of two diasteriomeric heptapeptides [Ac‐Ala‐Ala‐Ala‐(R/S)‐Cage‐Ala‐Ala‐Ala‐NH2] with a trishomocubane amino acid as a β‐turn scaffold are reported. The amino acid was synthesized as a racemate and two diastereomeric peptides were obtained. The two peptides were separated by preparative high‐pressure liquid chromatography and crystals suitable for X‐ray analysis were grown for both diasteriomeric peptides. In general, both the peptides satisfy the criteria for β‐turn conformations. Five of the six Ala residues of both cage peptide crystals satisfy the criteria for 310‐helix characteristics and the cage amino acid residue satisfied the α‐helix classification. These experimental results confirm previous theoretical studies in our laboratory which predicted that the cage moiety would be a strong/active β‐turn inducer.

Antiplasmodial sesquiterpene alkaloids from the roots of Maytenus mekongensis.

Eight new sesquiterpene alkaloids (1-8) and four known sesquiterpene alkaloids (9-12) have been isolated from the roots of Maytenus mekongensis. Structures were determined using extensive spectroscopic methods. The relative configuration of 7-epi-mekongensine (2) was established by single-crystal X-ray crystallographic analysis. The alkaloids were evaluated for antiplasmodial activity against Plasmodium falciparum, K1 strain, and for cytotoxicity using a panel of cell lines.