Sunil K. Ghosh

Resveratrol Metabolites Do Not Elicit Early Pro-apoptotic Mechanisms in Neuroblastoma Cells

Resveratrol, a nontoxic polyphenol, has been shown to inhibit tumor growth in a xenograft mouse model of neuroblasoma. However, resveratrol is rapidly metabolized, mainly to its glucuronidated and sulfated derivatives. This study demonstrates that resveratrol alone, and not the glucuronidated or sulfated metabolites, is taken up into tumor cells, induces a rise in [Ca(2+)](i), and ultimately leads to a decrease in tumor cell viability. A new water-soluble resveratrol formulation was delivered directly at the site of the tumor in a neuroblastoma mouse model. The amount of unmodified resveratrol associated with the tumor increased more than 1000-fold. The increase of unmodified resveratrol associated with the tumor resulted in tumor regression. The number of residual tumor cells that remained viable also decreased as the ratio of the metabolites relative to unmodified resveratrol declined.

Highly Regio- and Enantioselective Organocatalytic Conjugate Addition of Alkyl Methyl Ketones to a β-Silylmethylene Malonate

(S)-N-(2-pyrrolidinylmethyl)pyrrolidine/trifluoroacetic acid (3:1) combination catalyzed the direct addition of alkyl methyl ketones to beta-dimethyl(phenyl)silylmethylene malonate at the methyl terminal with high yield and excellent regio- and enantioselectivity. The silyl group played crucial roles in regioselection and substrate reactivity.

Gassman’s Intramolecular [2 + 2] Cationic Cycloaddition. Formal Total Syntheses of Raikovenal and epi-Raikovenal

The first intramolecular version of Gassmans cationic [2 + 2] cycloaddition employing vinyl acetals tethered to an unactivated olefin and its application in the formal syntheses of raikovenal and epi-raikovenal are described.

Developing a diastereoselective intramolecular [4+3] cycloaddition of nitrogen-stabilized oxyallyl cations derived from N-sulfonyl-substituted allenamides.

Efforts toward achieving a practical and diastereoselective intramolecular [4+3] cycloaddition of nitrogen-stabilized oxyallyl cations with tethered dienes are described. Epoxidation of N-sulfonyl substituted allenamides with dimethyldioxirane (DMDO) generates nitrogen-stabilized oxyallyl cations that readily undergo stereoselective [4+3] cycloaddition with dienes. Selectivity is found to depend on the tethering length as well as the stability of the oxyallyl cation intermediate, whether generated from N-carbamoyl- or N-sulfonyl-substituted allenamides. The use of chiral N-sulfonyl-substituted allenamides provided minimal diastereoselectivity in the cycloaddition, while high diastereoselectivity can be achieved with a stereocenter present on the tether. These studies provide further support for the synthetic utility of allenamides.

Tuning the Stability and the Reactivity of Substituted [3]Dendralenes for Quick Access to Diverse Copiously Functionalized Fused Polycycles with Step and Atom Economy

This is the first comprehensive study that details the synthesis of stable acyclic trisubstituted [3]dendralenes and deciphers their structural requisite for a successful diene transmissive Diels-Alder (DTDA) reaction by employing two different dienophiles and eventually generating a small repository of complex molecules, thus exemplifying how substituted [3]dendralenes could be deployed in diversity-oriented synthesis with high selectivities. A balance of reactivity and stability was struck by prudent selection of the position and nature of functional groups on these [3]dendralenes. Upon tandem Diels-Alder reactions with several symmetrical as well as unsymmetrical dienophiles, these dendralenes afforded diversity-oriented quick access to many polycyclic complex motifs possessing several functional groups and multiple stereogenic centers. Thus, the full potential of the dendralenes could be harnessed. The reactions proceeded under mild conditions with step and atom economy and were highly regio- and stereoselective besides being excellent yielding. The DTDA sequence resulted in the generation of four new carbon-carbon bonds, two new rings, and 3-7 stereogenic centers. The key feature of the method is that we could rapidly generate complexity along with functional and structural diversity from a trivial acyclic substrate with no stereogenic centers.