Matías L. Rodríguez

Regular and irregular sesquiterpenes containing a halogenated hydropyran from Laurencia caespitosa

Abstract The red seaweed Laurencia caespitosa is an unusually rich source of secondary metabolites. Five novel regular and irregular halogenated sesquiterpenes were isolated and characterized from this alga. The laucapyranoids A, B and C form a new class of rearranged terpenoids. The structures of laucapyranoids A and B were established by 1D and 2D NMR experiments, the latter being confirmed by X-ray crystallography. The identity of the unstable laucapyranoid C was established by reconstruction of its hydrodebrominated derivatives, whose structures were determined by spectroscopic data and X-ray analysis. The structures of the regular sesquiterpenoids 6-hydroxycaespitol and caespitane were elucidated from spectroscopic data and confirmed by X-ray analysis in the case of caespitane. Finally, the exciton chirality method was applied to the determination of the absolute configuration of caespitol and isocaespitol. The circular dichroism allylic benzoate approach circumvented the problems associated with the Bijvoet X-ray diffraction method in a previous study of these sesquiterpenes.

A unified stereochemical model for the polyepoxide cyclization route to marine polyether toxins

Abstract A stepwise intermediacy of oxocarbenium ions of type 2 provide strong support for the feasibility of the polyepoxide approach to ortho - and spiro -condensed polyether toxins of marine origin.

Intramolecular Nicholas Reaction: Stereoselective Synthesis of 5-Alkynylproline Derivatives

The intramolecular Nicholas reaction of propargylic alcohols derived from N, N-acyl-diprotected omega-semialdehydes obtained from glutamic acid provided stereoselectively 5-alkynylproline derivatives. The suitable choice of the N-protecting group (tosyl or benzoyl derivative) permitted control of the stereochemistry during the ring formation. Semiempirical calculations of the species involved in the cyclization support the observed stereochemistry.

Supramolecular assembly of diethyl 1H-pyrazole- 3,5-dicarboxylate 0.33-hydrate

In the title structure, C9H12N2O4·0.33H2O, the molxadecules are present as two conformers, one of which is disordered. Another type of disorder involves N—N—H/H—N—N tautomerism. Two crystallographically independent water molxadecules reside on a threefold axis and some water H atoms are also disordered. Six diethyl 1H-pyrazole-3,5-dicarboxylxadate molxadecules (three pairs of conformers) and two water molxadecules are assembled into a supraxadmolecular aggregate via N—H⋯N, Ow—H⋯N, Ow—H⋯Ow and N—H⋯Ow hydrogen bonds.

A new diterpene with two polymorphic modifications from a marine alga

A new diterpene, β-dictalediol monoacetate ( ), has been isolated from a brown alga X-ray crystal structure studies of have revealed the existence of two polymorphic modifications: dimorph in a chair/boat/chair conformation, and dimorph in a chair/chair/chair conformation

Hydrogen bonding in 3-methyl­enecyclo­hexane-1,1-dicarboxylic acid

As an extension of studies on hydrogen-bonding patterns in 7,7-R1/R2-5-hydroxymethyl-6-oxabicyclo-[3.2.1]octane-1carboxylic acid derivatives (Carrasco et al., 2001) compound (I) was isolated during the synthesis of dialkenyl/alkenyl = R1/ R2 derivatives as a product of the hydrolysis performed upon different esters (Pérez-Hernández et al., 2006). Inspection of the Cambridge Structural Database (Allen 2002, version 5.27) for 1,1-cyclohexanedicarboxylic acid derivatives reveals that only one compound, the spiro-(5.5)-undecane-3,3-dicarboxylic acid (CSD refcode DUTVET), has been reported (Duke et al., 1986), although no atomic coordinates are available.