Aurelio San Martin

Diterpenoids from Azorella compacta

In addition to mulinolic acid, a new diterpenoid, mulin-11,13-dien-20-oic acid, has been isolated from the aerial parts of Azorella compacta. Its structure was based on a spectroscopic comparison with mulinolic acid and on chemical grounds.

Tropane alkaloids from Schizanthus hookeri

Abstract Tropine, a pair of diastereoisomeric hygrolines and two new tropane alkaloids; 3α-senecioyloxytropan-6β-ol and 6β-angeloyloxytropan-3α-ol, were isolated from roots of Schizanthus hookeri .

Mulinol, A diterpenoid from Azorella compacta

Abstract In addition to mulinic acid, a new diterpenoid, mulinol has been isolated from the aerial parts of Azorella compacta . Its structure was based on spectroscopic comparison with mulinolic acid and chemical grounds.

Mulinolic acid, a diterpenoid from Mulinum crassifolium

Abstract Mulinolic acid, a new diterpenoid, has been isolated from the aerial parts of Mulinum crassifolium . Its structure was established by spectroscopic means. Mulinolic acid has a rearranged mulinane carbon skeleton of the type which has been found in four other diterpenoids from the same plant.

The isolation and structure determination of chilenone A, a putative dimer of 2-methyl-3(2H)-furanone from the marine alga

Abstract The isolation of chilenone A from Laurencia chilensis and the determination of its structure by spectral and x-ray crystallographic techniques is described.

The compound 14-keto-stypodiol diacetate from the algae Stypopodium flabelliforme inhibits microtubules and cell proliferation in DU-145 human prostatic cells.

We investigated the effects of the drug 14-keto-stypodiol diacetate (SDA) extracted from the seaweed product Stypopodium flabelliforme, in inhibiting the cell growth and tumor invasive behavior of DU-145 human prostate cells. In addition, the molecular action of the drug on microtubule assembly was analyzed. The effects of this diterpenoid drug in cell proliferation of DU-145 tumor cells in culture revealed that SDA at concentrations of 5 μM decreased cell growth by 14%, while at 45 μM a 61% decrease was found, as compared with control cells incubated with the solvent but in the absence of the drug. To study their effects on the cell cycle, DU-145 cells were incubated with increasing concentrations of SDA and the distribution of cell-cycle stages was analyzed by flow cytometry. Interestingly, the data showed that 14-keto-stypodiol diacetate dramatically increased the proportion of cells in the G2/M phases, and decreased the number of cells at the S phase of mitosis, as compared with appropriate controls. Studies on their action on the in vitro assembly of microtubules using purified brain tubulin, showed that SDA delayed the lag period associated to nucleation events during assembly, and decreased significantly the extent of polymerization. The studies suggest that this novel derivative from a marine natural product induces mitotic arrest of tumor cells, an effect that could be associated to alterations in the normal microtubule assembly process. On the other hand, a salient feature of this compound is that it affected protease secretion and the in vitro invasive capacity, both properties of cells from metastases. The secretion of plasminogen activator (u-PA) and the capacity of DU-145 cells to migrate through a Matrigel-coated membrane were significantly inhibited in the presence of micromolar concentrations of SDA. These results provide new keys to analyze the functional relationships between protease secretion, invasive behavior of tumor cells and the microtubule network.

Diastereoisomeric assignment in a pacifenol derivative using vibrational circular dichroism

The configuration of a chiral center in semisynthetic (-)-(2R,5R,5aR,8zeta,9aS)- 2,8-dibromo-2,5,9,9a-tetrahydro-5-hydroxy-5,8,10,10-tetramethyl-6H-2,5a-methano-1-benzoxepin-7(8H)-one (3 or 4), prepared in two steps from (-)-(2R,5R,5aR,7S,8S,9aS)-2, 7-dibromo-8-chloro-2,5,7,8,9,9a-hexahydro-5,8,10,10-tetramethyl-6H-2,5a-methano-1-benzoxepin-5-ol, known as pacifenol 1, has been determined using vibrational circular dichroism (VCD) measurements. The vibrational spectra (IR and VCD) of diastereoisomers 3 and 4 were calculated using density functional theory (DFT) at the B3LYP/DGDZVP level of theory for the two conformers that in each case account for the total energetic distribution found in the first 10 kcal/mol range. The DFT conformational optimization of the 8R diastereoisomer 3 indicates the cyclohexanone exists almost exclusively in a boat conformation with a beta-equatorial bromine atom and an alpha-axial methyl group at the chiral center alpha to the carbonyl group, while for the 8S diastereoisomer 4 a 5:1 conformational distribution in favor of a chair conformation with an alpha-axial bromine atom and a beta-equatorial methyl group is calculated, suggesting due to well-known chair versus boat relative stabilities that the plausible diastereoisomer would be the 8S molecule. A comparison of the IR spectrum of the reaction product with the calculated spectra of 3 and 4 provided no means for the diastereoisomeric assignment, while from comparison of the VCD spectra it became immediately evident that the rearranged molecule possesses the 8R absolute configuration as shown in 3, in concordance with a single crystal X-ray diffraction study that could be refined to an R-factor of 2.9%.

SECONDARY METABOLITES FROM MARINE PENICILLIUM BREVICOMPACTUM

In a screening of Basidiomycete cultures isolated from marine invertebrates collected along the Chilean coastline for the production of antibiotics we identified a Penicillium brevicompactum strain as a producer of metabolites inhibiting the growth of bacteria and fungi. Bioactivity guided purification resulted in the isolation of four known metabolites. Their structures were elucidated by spectroscopic methods

Santiagoside, the first asterosaponin from an antarctic starfish (Neosmilaster georgianus).

Abstract A new asterosaponin, named santiagoside ( 1 ), has been isolated from the Antarctic starfish Neosmilaster georgianus and, its structure elucidated on the basis of extensive spectroscopic experiments and chemical correlations. Santiagoside is the first asterosaponin possessing a tetrasaccharide sugar chain and a 1,4-disubstituted glucose unit.

Sterols from the gorgonianLephogorgia subcompressa

The free sterols of the gorgonianLephogorgia subcompressa were isolated and characterized by means of gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) techniques. The mixture contains C27 derivatives as the major sterols besides minor quantities of C26, C28, C29 compounds and also a C30 compound, gorgosterol.