Dharmender Singh

In(OTf)3 catalysed an expeditious synthesis of β-carboline–imidazo[1,2-a]pyridine and imidazo[1,2-a]pyrazine conjugates

β-Carboline containing alkaloids are ubiquitously present in Nature, while imidazo[1,2-a]pyridine nucleus is incorporated in various synthetic commercial drugs and biologically previliged moieties. On this basis, new β-carboline–imidazoazine conjugates were designed and a small library of compounds integrating both the pharmacophores was constructed with 4-points of diversity by using the In(OTf)3 assisted Groebke–Blackburn–Bienayme multicomponent strategy. The methodology was found to be simple and convenient for the efficient syntheses of β-carboline–imidazo[1,2-a]azine conjugates. The present synthetic protocol provides several advantages like operational simplicity, appreciable atom economy, short reaction time and easy purification procedure.

In(OTf)3 assisted synthesis of β-carboline C-3 tethered imidazo[1,2-a]azine derivatives

Synthesis of β-carboline based natural products and synthetic derivatives is one of the frontier areas of research owing to their medicinal properties. It is envisaged that 3-formyl-9H-β-carboline is a potential precursor and offers new vistas for the construction of a variety of heterocyclic architectures at the C-3 position of the β-carboline skeleton. In this context, an efficient protocol has been developed for the synthesis of β-carboline C-3 tethered imidazo[1,2-a]pyridine, imidazo[1,2-a]pyrimidine, and imidazo[1,2-a]pyrazine derivatives via exploration of the Groebke–Blackburn–Bienayme (GBB) reaction. The present protocol offers several advantages like operational simplicity, high atom economy, appreciable structural diversity and easy purification procedure.

Medicinal Attributes of Imidazo[1,2-a]pyridine Derivatives: An Update

The imidazo[1,2-a]pyridine scaffold is recognized as a privileged structure as it represents a promising area for identification of lead structures towards the discovery of new synthetic drug molecules. Several commercial drugs such as Zolpidem, Olprinone, Soraprazan and many other compounds in biological testing and preclinical evaluation, illustrate the wide therapeutic spectrum in this class of drug scaffolds. The present manuscript represents the assimilation of literature pertaining to medicinal aspects of this pharmacophore including the structure-activity relationships.

Metal-free 1,3-dipolar cycloaddition approach towards the regioselective synthesis of β-carboline and isoxazole based molecular hybrids

Nature has nourished β-carboline and isoxazole derivatives as privileged scaffolds and consequently they are ubiquitously found in alkaloids isolated from various sources. Moreover, several drug molecules based on them have been released in the market. Considering their immense impact, novel β-carboline–isoxazole-based molecular hybrids have been designed and a 1,3-dipolar cycloaddition strategy was devised to prepare the desired prototypes. A library of compounds with a wide range of diversity have been developed by employing β-carboline-containing dipolarophiles as well as dipoles. The current method represents a simple, efficient and easy-to-execute protocol towards the regioselective synthesis of β-carboline–isoxazole conjugates.

Considerations in the Choice of Mask Pattern Generation Technique

Pattern generation to generate masks after designing of a circuit is an important step in the manufacturing of integrated circuits. The input to pattern generator is a magnetic tape called PG tape and output is a reticle or full field IX mask.Pattern generation involves several issues such as economic viability of pattern generation systems as capital costs involved are very high, throughput considerations, the type of product or product mix to be manufactured eg, IX, 5X or 10X reticle, IX full field mask etc, complexity of device patterns, minimum feature size on masks, capability of pattern generation system to meet critical dimension, registration/overlay, permissible defect density- specification and process related issues. In this paper, an analysis of various pattern generation techniques has been done with respect to these issues.Criticality of the various issues with respect to a particular application has been studied. The study would help users of pattern generators to identify a pattern generat...

Printability of mask defects in negative resist projection photolithography

Abstract Yield loss and reliability problems due to mask defects in LSI/VLSI manufacture is one of the major concerns of today. The printability of mask defects on wafers depends mainly on type and size of mask defects, exposure technique and the resist system used, the various underlayers to be patterned and the etching technique adopted. The present paper investigates the printability of mask defects in negative resist projection photolithography for various underlayers, such as metal, polysilicon, nitride and oxide. A programmed defect mask has been used to study the ways in which various types and sizes of defects are transferred onto the wafer in projection aligner technology. The observations and results have been employed to predict the repair needs of masks and to understand the mask defect limited yield and reliability issues in LSI/VLSI.