الفهرس 
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Abstract
This thesis consists of four chapters:
Chapter 1:
Benzazoles, in particular, 1H-benzotriazole play a unique role in heterocyclic chemistry. 1H-Benzotriazole is an intriguing molecule that possesses interesting chemical and biological activities. Benzotriazole displays the characteristics of an ideal synthetic auxiliary and possesses both electron-donor and electron-acceptor properties.
Chapter 2:
This chapter describes the importance of halohydrin esters as intermediates in the synthesis of a wide range of biologically active natural and synthetic products including drugs, β-aminoalcohols, pyrrolidines and functionalized cyclopropanes.
This work describes an improved protocol for the regiospecific synthesis of pseudohalohydrin esters, with palladium catalysis under microwave-assisted, solvent-free conditions.
Microwave heating is a powerful tool in promoting a variety of applications in organic synthesis and functional group transformations without solvents.
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The use of a single-mode cavity microwave synthesizer helps achieve reproducibility, safety, reduced pollution, and simplicity in processing and handling.
Chapter 3:
This Chapter discusses the efficient preparation of chiral O-acyl isodipeptides from serine, which used in peptide ligations via different transition states.
The development of chemical ligation has facilitated the synthesis of large peptides by linking the C-terminus of one unprotected peptide with the N-terminus of another. Native chemical ligation (NCL), is a chemoselective and regioselective reaction of the thiolate of an N-terminal Cys-peptide with the carbon of a C-terminal thioester in another peptide that results in a native amide bond at the ligation site through a rapid NCL S- to N- acyl transfer via a cyclic transition state. The bifunctional nature of the N-terminal cysteine 1,2-mercaptoamine moiety is responsible for the observed chemoselectivity in NCL.
While of great importance, NCL has limitations that include the requirement of N-terminal cysteine residue at the ligation site to afford a peptide containing an internal cysteine. The low abundance of cysteine in human proteins (1.7% of the residues) also presents another limitation.
This work focused on serine which possesses the 1,2-hydroxylamine bifunctionality (mimicking the SH/NH2 bifunctionality of cysteine) and thus
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offers the possibility of chemoselective ligations by O- to N- acyl transfer without the need of cysteine residues.
Initially, two problems existed for the acylation of the hydroxyl group of serine: (i) difficulty in achieving O-acylation without epimerization (especially in solid-phase synthesis) and (ii) the facile hydrolysis of O-acyl serine ester linkages under the aqueous conditions of classical NCL. These problems were successfully overcome by the mild methodology for the preparation of chirally pure O-acyl isopeptides under anhydrous conditions.
Also this work demonstrates the classic O- to N-acyl shift via an eight-membered and eleven-membered transition states. Thus, “traceless”chemical ligation involving O- to N-acyl shift (at a Ser site) involving neither cysteine nor an auxiliary group at the ligation site has been achieved.
Chapter 4:
In addition this chapter describes the importance of peptides which display a wide variety of biological functions and many have marked physiological properties. For example, they function as structural molecules in tissues, as enzymes, antibodies, neurotransmitters, and hormones that control many physiological processes ranging from gastric acid segregation and carbohydrate metabolism to growth.