Guillermo M. Massanet

Potential allelopathic activity of several sesquiterpene lactone models

Abstract A collection of 12 natural and synthetic sesquiterpene lactones with eudesmanolide, melampolide, cis,cis -germacranolide, and guaianolide skeletons have been prepared and tested as allelochemicals. The effect of a series of aqueous solutions at 10 −4 -10 −9 M ofthis collection is evaluated. The specific structural requirements related to their activity is discussed. The natural sesquiterpene lactones soulangianolide A, melampomagnolide A and B, zaluzanin C and isozaluzanin C have been synthesized from costunolide, parthenolide and dehydrocostuslactone using SeO 2 and tert -butylhydroperoxide. The structures of the synthetic compounds were established by NMR spectroscopy.

Two sesquiterpene lactones from Centaurea canariensis

Abstract From the aerial part of Centaurea canariensis three sesquiterpene lactones were isolated: cynaropicrin, deacylcynaropicrin and aguerin A . The same species, grown from seed, yielded cynaropicrin, deacylcynaropicrin and aguerin B . The guaianolides aguerin A and B are reported for the first time. Aguerin B was subsequently found to be present in Centaureana linifolia, C. canariensis (var subspinnata ) and C. sventenii .

An efficient synthesis of furanocoumarins

Abstract An efficient synthesis of linear and angular furanocoumarins has been carried out starting from iodoumbelliferone derivatives. First synthesis of 6-iodoumbelliferone is described. The average yields are higher than those reported before.

Allylic Oxidation of Alkenes Catalyzed by a Copper–Aluminum Mixed Oxide

A strategy for the allylic oxidation of cyclic alkenes with a copper-aluminum mixed oxide as catalyst is presented. The reaction involves the treatment of an alkene with a carboxylic acid employing tert-butyl hydroperoxide as the oxidant. In all cases, the corresponding allylic esters are obtained. When L-proline is employed, the allylic alcohol or ketone is obtained. The oxidation of cyclohexene and valencene has been optimized by design of experiments (DoE) statistical methodology.

Enantioselective synthesis of α-hydroxyacids through oxidation of terminal alkenes with AD-mix/TEMPO

Abstract α-Hydroxyacids can be enantioselectively prepared by means of a two-step oxidation process, involving first the asymmetric dihydroxylation of a terminal alkene and subsequent oxidation with TEMPO/NaOCl/NaClO 2 in good to excellent yields. No fragmentation of the glycol intermediate was detected.

Enantioselective synthesis of arylmethoxyacetic acid derivatives

Abstract The preparation of several arylmethoxyacetic acids by a sequence of asymmetric dihydroxylation and further oxidation of the resulting glycol with TEMPO/NaClO/NaClO2 is described. The scope and limitations of the reaction are discussed.

Allelochemicals fromPilocarpus goudotianus leaves.

The effect on germination, shoot, and root growth by bergapten, xanthotoxin, imperatorin, xanthyletin, xanthoxyletin, luvangetin, donatin and alloxanthoxyletol fromPilocarpus goudotianus leaves, onLactuca sativa var. nigra seedlings has been evaluated. A structure-activity correlation is discussed based on the bioassay results. Furanocoumarins appear to be the most active compounds in comparison with pyrano- and simple coumarins. The presence of an oxygenated function at C-8 decreases the germination effect in furano- and pyranocoumarins, while C-5 substituents do not cause significant changes on the activity.

CeCl3/NaClO: a safe and efficient reagent for the allylic chlorination of terminal olefins

The preparation of allylic chlorides by reaction of terminal olefins with sodium hypochlorite in the presence of cerium trichloride heptahydrate is described. The scope, limitations and synthetic perspectives of the reaction are discussed.

An improved synthesis of 3-(1,1-dimethylallyl)coumarins

Abstract The syntheses of several 3-(1,1-dimethylallyl)coumarins, simple or bearing additional furan or pyran rings is achieved starting from the corresponding C-3 unsubstituted derivatives. The key step involves Ireland-Claisen rearrangements of allyl esters.

First synthesis of two naturally occurring oxetane lactones : clementein and clementein B

Abstract Clementein (1) and clementein B (2), sesquiterpene lactones with an 11,13-oxetane ring isolated from Centaurea clementei Boiss, have been synthesized from the α, β-unsaturated γ-lactone cynaropicrin (6). Conjugated photoaddition, stereoselective α-hydroxylation and mild cyclization to form the oxetane ring using THP as leaving group have been employed in this transformation.