Rosa L. Dorta

Intramolecular hydrogen abstraction. The use of organoselenium reagents for the generation of alkoxy radicals

Abstract The alkoxy radical intermediates, produced by photolysis of several hydroxy compounds in the presence of diphenylselenuranes (1) and iodine, undergo intramolecular hydrogen abstraction to afford cyclic ethers in good yield.

Hypervalent organoiodine reagents in the transannular functionalisation of medium-sized lactams: synthesis of 1-azabicyclo compounds

The amidyl radical intermediates, produced by photolysis of medium-sized lactams 7-heptanelactam (1), 8-octanelactam (3), and 9-nonanelactam (6) in the presence of (diacetoxyiodo)benzene (DIB) and iodine, undergo transannular hydrogen abstraction to afford intermolecularly functionalised compounds such as oxoindolizidines (4) and (5) and the 1-azabicyclo[5.3.0]decan-2-one (7) that are obtained in high yield from lactams (3) and (6), respectively.

1,3-TRANSPOSITION OF PRIMARY ALLYLIC ALCOHOLS : SYNTHESIS OF OPTICALLY ACTIVE SECONDARY AND TERTIARY ALLYLIC ALCOHOLS

Abstract The reduction of optically active 2,3-epoxy alcohols, suitably prepared by the Sharpless asymmetric epoxidation of primary allylic alcohols, with the system triphenylphosphine/iodine/imidazole/2,6-lutidine/water, leads in a single step to optically active secondary and tertiary allylic alcohols.

Stereochemical Properties of Glucosyl Sulfoxides in Solution

A series of alkyl β-glucosyl sulfoxides were synthesized and characterized in order to study their stereochemical properties. The dependence of the aglycon, solvent and absolute configuration of the sulfinyl group on the conformational properties around the glucosidic and C5-C6 (hydroxymethyl group) bonds were studied. The results for R(S) sulfoxides show linear correlations between the rotamer populations of the hydroxymethyl group and the corresponding Tafts steric parameter (E(S)) of the alkyl group attached to the sulfinyl group in polar and apolar solvents, an increase in the absolute value of E(S) leading to an increase in the gt population. In addition, NOE experiments reveal that as the bulkiness of the alkyl group increases the population of the g- rotamer increases, the latter stabilized by the exo-anomeric effect. These results are in complete agreement with the participation of the exo-anomeric effect in both conformational properties of R(S) sulfoxides. Sulfoxides with the S(S) configuration show different behavior to their R(S) epimers; thus, an increase in the E(S) value of the alkyl group leads to similar or lower gt populations in apolar solvents and to increases in gt in polar solvents. Their NOE studies reveal a conformational equilibrium (in polar and apolar solvents) between g- and g+, dependent on the size of the alkyl group R attached to the sulfinyl group. All these results for both epimers support the general hypothesis that the exo-anomeric effect modifies the conformation of the hydroxymethyl group, fulfills the stereoelectronic requirements, and shows dependence on the solvent.

Comparison of the conformational properties of carbasugars and glycosides: the role of the endocyclic oxygen

A series of carbasugars were prepared and their conformational properties studied by means of NMR spectroscopy. The results were compared to those previously found for O-, S-, and C-β-glycoside analogs. While the rotational populations of the hydroxymethyl group in O-, S-, and C-glycosides are known to depend on the structural nature of their aglycon, in carbasugars it proved to be independent of the pseudo-aglycon. This result confirms that endocyclic oxygen is necessary for the observed relationship between the structure of the aglycon and the rotational populations of the hydroxymethyl group, and indicates that the stereoelectronic exo-anomeric effect is mainly responsible for such conformational dependence.

Synthetic menthyl α/β-(1→6)-diglucopyranosides-induced cell death in human leukemia cells is dependent on caspases

A series of alkyl α/β-(1→6)-diglucopyranosides 1-12 were synthesized and assessed for cytotoxicity against HL-60, U937, Molt-3 and MCF-7 cancer cell lines. The menthyl derivatives displayed strong cytotoxic properties showing IC(50) values between 6 and 16 μM. Furthermore, we demonstrated that the selected synthetic (+)-menthyl β-(1→6)-diglucopyranoside 5 induces apoptotic cell death in human leukemia cells through a mechanism that involves activation of multiple caspases. Cell death was completely prevented by the non-specific caspase inhibitor z-VAD-fmk and found to be associated with the release of cytochrome c, an increase in the expression of Bax levels and a decrease in the generation of reactive oxygen species.