Surajit Sinha

Small-molecule inhibitors reveal multiple strategies for Hedgehog pathway blockade

Inappropriate activation of the Hedgehog (Hh) signaling pathway has been implicated in a diverse spectrum of cancers, and its pharmacological blockade has emerged as an anti-tumor strategy. While nearly all known Hh pathway antagonists target the transmembrane protein Smoothened (Smo), small molecules that suppress downstream effectors could more comprehensively remediate Hh pathway-dependent tumors. We report here four Hh pathway antagonists that are epistatic to the nucleocytoplasmic regulator Suppressor of Fused [Su(fu)], including two that can inhibit Hh target gene expression induced by overexpression of the Gli transcription factors. Each inhibitor has a unique mechanism of action, and their phenotypes reveal that Gli processing, Gli activation, and primary cilia formation are pharmacologically targetable. We further establish the ability of certain compounds to block the proliferation of cerebellar granule neuron precursors expressing an oncogenic form of Smo, and we demonstrate that Hh pathway inhibitors can have tissue-specific activities. These antagonists therefore constitute a valuable set of chemical tools for interrogating downstream Hh signaling mechanisms and for developing chemotherapies against Hh pathway-related cancers.

Versatile Synthesis and Rational Design of Caged Morpholinos

Embryogenesis is regulated by genetic programs that are dynamically executed in a stereotypic manner, and deciphering these molecular mechanisms requires the ability to control embryonic gene function with similar spatial and temporal precision. Chemical technologies can enable such genetic manipulations, as exemplified by the use of caged morpholino (cMO) oligonucleotides to inactivate genes in zebrafish and other optically transparent organisms with spatiotemporal control. Here we report optimized methods for the design and synthesis of hairpin cMOs incorporating a dimethoxynitrobenzyl (DMNB)-based bifunctional linker that permits cMO assembly in only three steps from commercially available reagents. Using this simplified procedure, we have systematically prepared cMOs with differing structural configurations and investigated how the in vitro thermodynamic properties of these reagents correlate with their in vivo activities. Through these studies, we have established general principles for cMO design and successfully applied them to several developmental genes. Our optimized synthetic and design methodologies have also enabled us to prepare a next-generation cMO that contains a bromohydroxyquinoline (BHQ)-based linker for two-photon uncaging. Collectively, these advances establish the generality of cMO technologies and will facilitate the application of these chemical probes in vivo for functional genomic studies.

The Imidazopyridine Derivative JK184 Reveals Dual Roles for Microtubules in Hedgehog Signaling

Eradicating hedgehogs: The title molecule has been previously identified as a potent inhibitor of the Hedgehog signaling pathway, which gives embryonic cells information needed to develop properly. This molecule is shown to modulate Hedgehog target gene expression by depolymerizing microtubules, thus revealing dual roles of the cytoskeleton in pathway regulation (see figure).

Progress in the Synthesis of Iboga-alkaloids and their Congeners

I. Structure and Pharmacological Properties of Iboga-alkaloids ....... 542 1. Structure of Iboga-alkaloids..................................................................542 2. Newly Isolated Iboga-alkaloids..............................................................544 3. Newly Isolated Iboga-lignan Conjugated Natural Products.....................545 4. Pharmacological Properties of Iboga-alkaloids ......................................546 II. Syntheses of Ibogaine, Ibogamine (Ibogamine-19-ol) and their Analogues ..................................................................................... 547 1. Brief Outline of the Retrosynthetic Strategies.........................................547 2. Electrophilic C2–C16 Cyclization Approach...........................................548 3. Fischer Indolization Approach ..............................................................551 4. Mixed Metal-Mediated Cyclization Approach.........................................553 5. Formation by Hydroazepine Ring ..........................................................556 6. Decarboxylation of Coronaridine ..........................................................557 III. Syntheses of Coronaridine, Catharanthine and their Analogs........ 557 1. Brief Outline of the Retrosynthetic Strategies.........................................557 2. Synthesis from Ibogamine and Cleavamine............................................558 a) From Ibogamine............................................................................558 b) From Cleavamines ........................................................................558 c) Cleavamines .................................................................................559 3. Diels-Alder Reaction Mediated Synthesis ...............................................562 IV. Concluding Remarks .................................................................... 569 Acknowledgements ....................................................................... 569 References .................................................................................... 569

The prop-2-ynyloxy carbonyl function (POC): A new amino-protecting group removable from sulfur-containing peptides by ultrasonic irradiation with tetrathiomolybdate under mild and neutral conditions

Abstract The prop-2-ynyloxy carbonyl function (POC) which can be cleaved under mild and neutral conditions in the presence of benzyltriethylammonium tetrathiomolybdate has been developed as a new protecting group for amines.

One pot conversion of alcohols to disulfides mediated by benzyltriethylammonium tetrathiomolybdate

Abstract A one pot conversion of alcohols to disulfides in good yields via the activation of a hydroxyl group with DCC or P(NMe 2 ) 3 / CCl 4 followed by treatment with benzyltriethylammonium tetrathiomolybdate is reported.

Synthesis of optically active 2- and 3- indolylglycine derivatives and their oxygen analogues.

2-Indolylglycine derivative and its oxygen analogue have been synthesized by Sonogashira coupling followed by cyclization in one pot between 2-iodoheteroarenes and ethynyloxazolidinone where 3-indolylglycine derivative and its oxygen analogue have been synthesized from silylated internal alkyne using Larocks heteroannulation as the key reaction.

Improved Protocol for the Synthesis of Flexibly Protected Morpholino Monomers from Unprotected Ribonucleosides

An inexpensive and much improved protocol has been developed for the synthesis of protected morpholino monomers from unprotected ribonucleosides in high overall yield, using oxidative glycol cleavage and reductive amination strategy. Unlike the previous methods, the present strategy allows installing the exocyclic amine protections at a later stage, and thus avoids the use of expensive, or commercially unavailable, exocyclic amine-protected ribonucleosides as starting materials. To demonstrate the flexibility of the present method in choosing protecting groups, the monomers have been protected with several such groups of different deblocking properties at the exocyclic amine position.

Tunability of monodispersed intermetallic AuCu nanoparticles through understanding of reaction pathways

Synthesis of size selective monodispersed nanoparticles particularly intermetallic with well-defined compositions represents a challenge. This paper presents a way for the synthesis of intermetallic AuCu nanoparticles as a model system. We show that reduction of Au and Cu precursors is sensitive to the ratio of total molar concentrations of surfactant to metal precursors. A careful design of experiments to understand the kinetics of the reduction process reveals initial formation of seed nanoparticles of pure Au. Reduction of Cu occurs on the surface of the seed followed by diffusion to yield AuCu. This understanding allows us to develop a two step synthesis where the precise size controlled seed of Au nanoparticles produced in the first step is used in the second step reaction mixture as an Au precursor to allow deposition and interdiffusion of Cu that yields size selected AuCu intermetallics of sub 10 nm sizes.

5-Propynyluracil·diaminopurine: an efficient base-pair for non-enzymatic transcription of DNA

The Up.D base-pair (5-propynyl uracil.diaminopurine) is found to be more effective at non-enzymatic transcription than the corresponding natural T.A pair; under non-enzymatic reaction conditions where the natural T.A base-pair fails, a DNA template bearing Up efficiently directs the incorporation of D into a product RNA strand.