C. V. Ramana

Small molecule inhibition of phosphatidylinositol-3,4,5-triphosphate (PIP3) binding to pleckstrin homology domains

The PI3-kinase (PI3K) pathway regulates many cellular processes, especially cell metabolism, cell survival, and apoptosis. Phosphatidylinositol-3,4,5-trisphosphate (PIP3), the product of PI3K activity and a key signaling molecule, acts by recruiting pleckstrin-homology (PH) domain-containing proteins to cell membranes. Here, we describe a new structural class of nonphosphoinositide small molecule antagonists (PITenins, PITs) of PIP3–PH domain interactions (IC50 ranges from 13.4 to 31 μM in PIP3/Akt PH domain binding assay). PITs inhibit interactions of a number of PIP3-binding PH domains, including those of Akt and PDK1, without affecting several PIP2-selective PH domains. As a result, PITs suppress the PI3K-PDK1-Akt pathway and trigger metabolic stress and apoptosis. A PIT-1 analog displayed significant antitumor activity in vivo, including inhibition of tumor growth and induction of apoptosis. Overall, our studies demonstrate the feasibility of developing specific small molecule antagonists of PIP3 signaling.

Pd(II)-mediated alkynediol spiroketalization: first total synthesis of (-)-cephalosporolide E and (+)-cephalosporolide F.

Herein we describe a concise assembly of the central 1,6-dioxaspiro[4.4]nonane core of cephalosporolides E/F by employing a Pd-mediated alkynediol cycloisomerization and their total synthesis. On the basis of spectroscopic data and optical rotation values, the absolute configurations of cephalosporolides E/F were proposed.

Total synthesis and determination of relative and absolute configuration of multiplolide A

A flexible approach for total syntheses of possible multiplolide A diastereomers establishing the relative and absolute configuration is documented. The adopted strategy features ring-closing metathesis (RCM) as the key reaction and screening of a set of substrates for the feasibility of RCM in general and for the requisite E-configuration of ring olefin in particular. Selective protecting groups manipulation prior to the assembly of the central macrocyclic core was instrumental in installing the epoxide functionality on a fully deprotected nonenolide at the end of the synthesis.

A novel and simple asymmetric synthesis of CMI-977 (LDP-977): a potent anti-asthmatic drug lead

Abstract A practical gram scale asymmetric synthesis of CMI-977 is described. A tandem double elimination of an α-chlorooxirane and concomitant intramolecular nucleophilic substitution was used as the key step. Jacobsen hydrolytic kinetic resolution and Sharpless asymmetric epoxidation protocols were applied for the execution of the synthesis of the key chiral building block.

First synthesis of methyl α-C-D-arabinofuranosyl-(1→5)-α-D-arabinofuranoside: the C-disaccharide segment of motif C of Mycobacterium tuberculosis

Abstract The synthesis of C -analogue of the disaccharide 2 α-ara f -(1→5)-ara f , present in motif C of the arabino-galactan portion of Mycobacterium tuberculosis , has been described. The critical Cue5f8C bond formation reaction to couple both the furanosyl residues has been accomplished through nitro-aldol condensation.

Total synthesis of (-)-sacidumlignans B and D.

The first total synthesis of naturally occurring sacidumlignans A (1), B (2), and D (4) was executed and the absolute configuration of 2 and 4 was determined. A diastereoselective α- methylation of a lactone was used as the key step for the control of the chiral centers of the central lignan core. An acid mediated dehydrative cyclization of an aldehyde to construct the dihydronaphthalene unit of 2 and the aromatization of the intermediate dihydronaphthalene derivative to synthesize 1 are the key reactions employed in this regard.

“Click” synthesis of isomeric compounds for assessing the efficiency of the bifurcated Br⋯NO2 synthon

We report herein the extention of the azide–alkyne “click reaction” to crystal engineering and synthesize a collection of isomeric compounds with modular positioning of Br and NO2 on a tricyclic template and crystal structural analyses of the derived isomers. It is quite remarkable to notice that none of the isomers displayed the bifurcated three-center NO2⋯Br supramolecular synthon in their crystal structures

A Carbohydrate-Based Approach for the Total Synthesis of Aculeatin D and 6-epi-Aculeatin D

A concise approach for the total synthesis of aculeatin D and 6-epi-aculeatin D employing differentially protected anti, anti-1,3,5-triol alkyne prepared from alpha-D-glucoheptonic-gamma-lactone derivative is documented. Phenol protecting group manipulation for selective O-debenzylation during the hydrogenation of the diyne intermediate and one-pot phenolic oxidation with concomitant spiroketalization highlight the accomplished total synthesis.

Evaluation of viability of halogen⋯O2N interactions: Insight from crystal packing in a series of isomeric halo and nitro substituted triaryl compounds with modular positioning of halogen and NO2 groups

A series of isomeric triaryl compounds with a modular positioning of the halogen and NO2 groups have been synthesized by the azide–alkyne “click reaction” and have been characterized by single crystal X-ray structure analysis. This isomeric series has provided an opportunity for understanding the efficiency of the bifurcated halogen⋯NO2 synthon in the organization of the molecules in the crystalline lattice. The changes in molecular conformation, crystal packing and supramolecular aggregation due to the change in the relative positioning of the complementary groups, halogen atom and the NO2 group on ring A and ring C respectively, have been discussed. All the isomers synthesized are crystalline and establish the triazole as a reliable linker for crystal engineering oriented molecular synthesis. The 2-NO2 derivatives display in general, a helical architecture and 3-NO2 derivatives exhibit a centrosymmetric dimeric assembly via the complementary C–H⋯O interactions leading to either a helical or a 2-dimensional sheet pattern. The molecular organization in 4-NO2 derivatives revealed in general a 2D sheet pattern.

An expedient synthesis of tetrakis (cyclopropylmethyl) methane

Synthesis of tetrakis(cyclopropylmethyl)methane, a new symmetric product has been described using the radical mediated gem-diallylation of cyclopropylmethyl xanthate as a key step and its single crystal X-ray analysis established its C2-symmetry.