New umbelliferone sesquiterpene ethers from roots ofLigularia persica

An extract of roots of Ligularia persica yielded thirteen umbelliferone sesquiterpene ethers, among them the new ones ligupersin A (11) and ligupersin B (13).

Ein neues Butenolid ausConyza bonariensis

A New Butenolide from Conyza bonariensis Extraction of aerial parts of Conyza bonariensis and chromatographic separation yielded the new butenolide 1, together with the acetylenic compounds trans-lachnophyllum lactone (2) and cis-lachnophyllum methyl ester (3), and the germacrane alcohol 4.

Recent Advances in the Field of Naturally Occurring 5,6-Dihydropyran-2-ones

ChemInform Abstract: Diastereoselectivity in Organometallic Additions to the Carbonyl Group of Protected Erythrulose Derivatives.

We have investigated a number of nucleophillic additions to l-erythrulose derivatives (4−12) bearing protective O-silyl, O-benzyl, and O-trityl groups in various relative positions. The results are discussed in the frame of chelated vs nonchelated transition states with additional support of previously published theoretical calculations. Sound evidence appears to exist for the formation of α-chelates as the key intermediates in nucleophillic additions to these α,β-dioxygenated ketones. Since such evidence is still lacking in the case of β-chelates, proposals of their intermediacy have been relegated in favor of the more solid Felkin−Anh model, which predicts the same stereochemical result. …

Comparative Analysis of the Vascular Actions of Diterpenes Isolated from Euphorbia canariensis

Abstract We have analysed the effects of 2,3-diepiingol 7,12-diacetate-8-isobutyrate (compound 1), ingenol-3-angelate-17-benzoate (compound 2), ingenol-3-angelate-17-benzoate-20-acetate (compound 3) and 3,5,7,8,9,15-hexahydroxyjatropha-6(17),11-dien-14-one-5,8-bis(2-methylbutyrate)-7-(2-methylpropionate) (compound 4), four diterpenes isolated from E. canariensis, on the isometric tension developed by isolated rabbit basilar and carotid arteries. Concentration-response curves to these compounds were obtained cumulatively in both arteries at resting tension and active tone (KCl, 50 mM). At resting tension a concentration-dependent contraction was induced by the four compounds. In the basilar …

Aldol Reactions with Erythrulose Derivatives: Stereoselective Synthesis of Differentially Protected syn -α,β-Dihydroxy Esters

Boron enolates of 1-O-silylated erythrulose 3,4-acetonides prepared with Brown's chloro-dicyclohexylborane/tertiary amine system have been shown to react with achiral aldehydes in a highly stereoselective way to yield a 1,2-syn/1,3-syn stereoisomer. Through oxidative cleavage of the aldol adducts with periodic acid hydrate, enantiopure syn-α,β-dihydroxy esters with either hydroxyl group differently protected have been prepared. These erythrulose derivatives therefore behave as a chiral hydroxy acetate (glycolate) enolate equivalent.

ChemInform Abstract: New Umbelliferone Sesquiterpene Ethers from Roots of Ligularia persica.

An extract of roots of Ligularia persica yielded thirteen umbelliferone sesquiterpene ethers, among them the new ones ligupersin A (11) and ligupersin B (13).

2.14 Selected Diastereoselective Reactions: Enolate Alkylation

This chapter discusses processes in which enolates are subjected to reaction with alkylating reagents. In all the processes examined here, at least one of the two reaction components is chiral and the reaction gives rise to one or more diastereomeric compounds. In most cases, the enolate is generated through deprotonation of the corresponding carbonyl precursor with a suitable base, but in several cases, the enolate is generated differently, for example, through Michael addition of a nucleophile to a conjugated carbonyl compound. The various factors that have been found to influence the stereochemical outcome of the alkylation reaction in a measurable way are also discussed. The material ha…

New acetylenes fromChrysanthemum coronarium L.

The investigation of the aerial parts of Chrysanthemum coronarium yielded, in addition to several known compounds, two new acetylenic sulfoxides 9 and 10, and a new thiophene spiroacetal enol ether 11. Their structures were deduced by spectroscopic and chemical methods.

ChemInform Abstract: Aldol Reactions with Erythrulose Derivatives: Stereoselective Synthesis of Differentially Protected syn-α,β-Dihydroxy Esters.

Boron enolates of 1-O-silylated erythrulose 3,4-acetonides prepared with Brown's chloro-dicyclohexylborane/tertiary amine system have been shown to react with achiral aldehydes in a highly stereoselective way to yield a 1,2-syn/1,3-syn stereoisomer. Through oxidative cleavage of the aldol adducts with periodic acid hydrate, enantiopure syn-α,β-dihydroxy esters with either hydroxyl group differently protected have been prepared. These erythrulose derivatives therefore behave as a chiral hydroxy acetate (glycolate) enolate equivalent.

An ab initio study of the enolboration of 3-pentanone mediated by boron monochlorides L2BCl

Abstract Using ab initio methods at the HF/6-31G∗∗ level, we have studied the mechanism of the enolboration of 3-pentanone mediated by boron monochlorides L2BCl (L=H, methyl and isopropyl) and trimethyl amine. The size of the L group has been found to have a decisive influence on the configuration (E or Z) of the formed boron enolate. Thus, whereas our calculations predict that dimethylboron chloride yields the Z enolate with high stereoselectivity, diisopropylboron chloride is found to yield predominantly the E enolate. The difference in behavior is due mainly to steric features related to the conformational bias of the respective ketone–boron chloride complexes formed reversibly in the fi…

ChemInform Abstract: New Eudesmane Derivatives from Artemisia tournefortiana

Extraction of the aerial parts of Artemisia tournefortiana Reichb. yields a new cis-eudesmanolide 4 and three new eudesmane acids 7, 8, and 10, together with several known compounds. Their structures were deduced by spectroscopic and chemical methods.

ChemInform Abstract: New Acetylenes from Chrysanthemum coronarium L.

The investigation of the aerial parts of Chrysanthemum coronarium yielded, in addition to several known compounds, two new acetylenic sulfoxides 9 and 10, and a new thiophene spiroacetal enol ether 11. Their structures were deduced by spectroscopic and chemical methods.

Enantioselective synthesis and absolute configurations of aculeatins A, B, D, and 6-epi-aculeatin D

The three naturally occurring, bioactive spiroacetals aculeatins A, B, and D, as well as the non-natural 6-epi-aculeatin D have been synthesized for the first time in enantiopure form using an asymmetric allylation as the only chirality source. A further key step was a stereoselective aldol reaction with remote induction. The absolute configurations of the natural products have been established and an erroneous structural assignment has been corrected.

Diastereoselectivity in Organometallic Additions to the Carbonyl Group of Protected Erythrulose Derivatives

We have investigated a number of nucleophillic additions to L-erythrulose derivatives (4-12) bearing protective O-silyl, O-benzyl, and O-trityl groups in various relative positions. The results are discussed in the frame of chelated vs nonchelated transition states with additional support of previously published theoretical calculations. Sound evidence appears to exist for the formation of alpha-chelates as the key intermediates in nucleophillic additions to these alpha,beta-dioxygenated ketones. Since such evidence is still lacking in the case of beta-chelates, proposals of their intermediacy have been relegated in favor of the more solid Felkin-Anh model, which predicts the same stereoche…

Synthesis of honokiol analogues and evaluation of their modulating action on VEGF protein secretion and telomerase-related gene expressions

A group of 36 biphenyl derivatives structurally related to honokiol were synthesized by means of Suzuki coupling reactions. Their cytotoxicities were evaluated and compared to that of honokiol. Some of the compounds were then evaluated for their ability to downregulate the secretion of the VEGF protein and the expression of the VEGF, hTERT, and c-Myc genes; the two latter involved in the activation of telomerase in tumoral cells. Some of the synthetized derivatives showed promising pharmacological features as they exhibited IC50 values in low micromolar range, good therapeutic margins, and a multiple mode of action on tumor cells based on the inhibition of VEGF and, at the same time, of the…

New eudesmane derivatives fromArtemisia tournefortiana

Extraction of the aerial parts of Artemisia tournefortiana Reichb. yields a new cis-eudesmanolide 4 and three new eudesmane acids 7, 8, and 10, together with several known compounds. Their structures were deduced by spectroscopic and chemical methods.