Bhubaneswar Mandal

Ethyl 2-cyano-2-(4-nitrophenylsulfonyloxyimino)acetate-mediated Lossen rearrangement: single-pot racemization-free synthesis of hydroxamic acids and ureas from carboxylic acids.

Ethyl 2-cyano-2-(4-nitrophenylsulfonyloxyimino)acetate (4-NBsOXY) mediated Lossen rearrangement and its application for the synthesis of ureas is demonstrated. Required hydroxamic acids for the Lossen rearrangements were synthesized from carboxylic acids using the same reagent. Finally, reaction of an amine with the produced isocyanate resulted in urea. Good yields without racemization were achieved under milder and simpler reaction conditions. Reactions are compatible with common N-protecting groups, such as Boc, Fmoc, Cbz, and benzyl, as well as various OH protecting groups, such as (t)Bu and Bzl. Conversion from carboxylic acid to urea is achieved in one pot. Most importantly, byproducts Oxyma [ethyl 2-cyano-2-(hydroxyimino)acetate] and 4-nitrobenzenesulfonic acid can be recovered easily and can be recycled to prepare the reagent. Thus, the method is environmentally friendly and cost-effective.

Switch-Peptides : Design and Characterization of Controllable Super-Amyloid-Forming Host-Guest Peptides as Tools for Identifying Anti-Amyloid Agents

Several amyloid‐forming proteins are characterized by the presence of hydrophobic and highly amyloidogenic core sequences that play critical roles in the initiation and progression of amyloid fibril formation. Therefore targeting these sequences represents a viable strategy for identifying candidate molecules that could interfere with amyloid formation and toxicity of the parent proteins. However, the highly amyloidogenic and insoluble nature of these sequences has hampered efforts to develop high‐throughput fibrillization assays. Here we describe the design and characterization of host–guest switch peptides that can be used for in vitro mechanistic and screening studies that are aimed at discovering aggregation inhibitors that target highly amyloidogenic sequences. These model systems are based on a host–guest system where the amyloidogenic sequence (guest peptide) is flanked by two β‐sheet‐promoting (Leu‐Ser)n oligomers as host sequences. Two host–guest peptides were prepared by using the hydrophobic core of Aβ comprising residues 14–24 (HQKLVFFAEDV) as the guest peptide with switch elements inserted within (peptide 1) or at the N and C termini of the guest peptide (peptide 2). Both model peptides can be triggered to undergo rapid self‐assembly and amyloid formation in a highly controllable manner and their fibrillization kinetics is tuneable by manipulating solution conditions (for example, peptide concentration and pH). The fibrillization of both peptides reproduces many features of the full‐length Aβ peptides and can be inhibited by known inhibitors of Aβ fibril formation. Our results suggest that this approach can be extended to other amyloid proteins and should facilitate the discovery of small‐molecule aggregation inhibitors and the development of more efficacious anti‐amyloid agents to treat and/or reverse the pathogenesis of neurodegenerative and systemic amyloid diseases.

Functional Characterization of the Odorant Receptor 51E2 in Human Melanocytes.

Olfactory receptors, which belong to the family of G-protein-coupled receptors, are found to be ectopically expressed in non-sensory tissues mediating a variety of cellular functions. In this study we detected the olfactory receptor OR51E2 at the transcript and the protein level in human epidermal melanocytes. Stimulation of primary melanocytes with the OR51E2 ligand β-ionone significantly inhibited melanocyte proliferation. Our results further showed that β-ionone stimulates melanogenesis and dendritogenesis. Using RNA silencing and receptor antagonists, we demonstrated that OR51E2 activation elevated cytosolic Ca2+ and cAMP, which could mediate the observed increase in melanin synthesis. Co-immunocytochemical stainings using a specific OR51E2 antibody revealed subcellular localization of the receptor in early endosomes associated with EEA-1 (early endosome antigen 1). Plasma membrane preparations showed that OR51E2 protein is present at the melanocyte cell surface. Our findings thus suggest that activation of olfactory receptor signaling by external compounds can influence melanocyte homeostasis.

Ethyl 2-Cyano-2-(2-nitrobenzenesulfonyloxyimino)acetate (o-NosylOXY): A Recyclable Coupling Reagent for Racemization-Free Synthesis of Peptide, Amide, Hydroxamate, and Ester

Ubiquitousness of amide and ester functionality makes coupling reactions extremely important. Although numerous coupling reagents are available, methods of preparation of the common and efficient reagents are cumbersome. Those reagents generate a substantial amount of chemical waste and lack recyclability. Ethyl 2-cyano-2-(2-nitrobenzenesulfonyloxyimino)acetate (o-NosylOXY), the first member of a new generation of coupling reagents, produces byproducts that can be easily recovered and reused for the synthesis of the same reagent, making the method more environmentally friendly and cost-effective. The synthesis of amides, hydroxamates, peptides, and esters using this reagent is described. The synthesis of the difficult sequences, for example, the islet amyloid polypeptide (22-27) fragment (with a C-terminal Gly, H-Asn-Phe-Gly-Ala-Ile-Leu-Gly-NH2) and acyl carrier protein (65-74) fragment (H-Val-Gln-Ala-Ala-Ile-Asp-Tyr-Ile-Asn-Gly-OH), following the solid-phase peptide synthesis (SPPS) protocol and Amyloid β (39-42) peptide (Boc-Val-Val-IIe-Ala-OMe), following solution-phase strategy is demonstrated. Remarkable improvement is noticed with respect to reaction time, yield, and retention of stereochemistry. A mechanistic investigation and recyclability are also described.

Reversal of aggregation using β-breaker dipeptide containing peptides: Application to Aβ(1-40) self-assembly and its inhibition.

Reversion of protein or peptide aggregation is a formidable task, important in various domains of research at the interface of chemistry, medicine, and nanoscience. A novel class of dipeptides, termed as β-breaker dipeptides (BBDPs), is identified, which can be incorporated into the self-recognizing sequences to generate a novel class of conformational switch which forms β-sheet at an initial stage and then converts in a controlled manner to random coil at specific conditions. Incorporation of BBDPs in a well designed amyloidogenic peptides generates a special class of β-sheet breaker peptides those undergo a chemical change at physiological condition generating a breaker element in situ. These β-breaker peptides are shown to first incorporate into the amyloid and then disrupt it. Such conformational switches may be used to study agrregation/disaggregation process and may find many biomedical applications relevant to aggregation related disorders. Such strategy for reversion of peptide aggregation using chemical tricks may find application in material chemistry as well.

Dynamic Combinatorial Enrichment of Polyconformational D‐/L‐Peptide Dimers

D-/L-peptides such as gramicidin A (gA) adopt unique dimeric β-helical structures of different topologies. To overcome their conformational promiscuity and enrich individual components, a dynamic combinatorial approach assisted by thiol tags was developed. This method led to identification of the preferential formation of antiparallel dimers under a broad range of conditions, which was independent of peptide side-chain polarity. Exclusive formation of an antiparallel cyclic dimer was achieved in the presence of cesium ions.

Waste reduction in amide synthesis by a continuous method based on recycling of the reaction mixture

In this article, a new one pot synthesis of amides is demonstrated. Potential of the recovery and reuse strategy for waste reduction is examined. Finally, a new strategy is proposed where the whole reaction mixture containing the catalyst, the solvent (auxiliary) and the unreacted starting material is recovered by precipitating the product using ethanol and reused for the next cycle in a continuous operation protocol.

Disaggregation of Amylin Aggregate by Novel Conformationally Restricted Aminobenzoic Acid containing α/β and α/γ Hybrid Peptidomimetics

Diabetes has emerged as a threat to the current world. More than ninety five per cent of all the diabetic population has type 2 diabetes mellitus (T2DM). Aggregates of Amylin hormone, which is co-secreted with insulin from the pancreatic β-cells, inhibit the activities of insulin and glucagon and cause T2DM. Importance of the conformationally restricted peptides for drug design against T2DM has been invigorated by recent FDA approval of Symlin, which is a large conformationally restricted peptide. However, Symlin still has some issues including solubility, oral bioavailability and cost of preparation. Herein, we introduced a novel strategy for conformationally restricted peptide design adopting a minimalistic approach for cost reduction. We have demonstrated efficient inhibition of amyloid formation of Amylin and its disruption by a novel class of conformationally restricted β-sheet breaker hybrid peptidomimetics (BSBHps). We have inserted β, γ and δ -aminobenzoic acid separately into an amyloidogenic peptide sequence, synthesized α/β, α/γ and α/δ hybrid peptidomimetics, respectively. Interestingly, we observed the aggregation inhibitory efficacy of α/β and α/γ BSBHps, but not of α/δ analogues. They also disrupt existing amyloids into non-toxic forms. Results may be useful for newer drug design against T2DM as well as other amyloidoses and understanding amyloidogenesis.

Amyloid β derived switch-peptides as a tool for investigation of early events of aggregation: a combined experimental and theoretical approach

Alzheimers disease, a severe neurodegenerative disorder, is believed to be caused by the interneuronal aggregation of the amyloid β peptide. It has no cure yet. Despite rigorous research, the mechanism of aggregation is not yet fully delineated. Especially probing the early events of the aggregation is difficult as we have no control on the kinetics of the process of aggregation. We have used amyloid β derived switch-peptides that behave as the functional mimic of the amyloid β peptide, and demonstrated that side chain aromatic interactions precede the β-sheet formation resulting in fibrillization. Detailed investigation into the early events of aggregation has become possible as the kinetics of aggregation of the switch-peptides can be controlled. We have used ultraviolet (UV) spectroscopy, circular dichroism (CD), Raman spectroscopy and Molecular Dynamics (MD) simulation as a combined experimental and theoretical approach.

Synthesis of O-benzyl hydroxamates employing the sulfonate esters of N-hydroxybenzotriazole

The direct conversion of various carboxylic acids, that include sterically hindered amino acids and di-peptides, to O-benzyl hydroxamates is demonstrated using sulfonate esters of benzotriazoles under ambient and milder conditions without significant racemization. This simple and efficient protocol is extended to the synthesis of O-benzyl hydroxamates, using in situ generated solid supported TsOBt to facilitate the recovery and re-usability of HOBt and to render the isolation of the products easier. Such in situ generation and further application of a coupling reagent is novel and industrially important.