Synthesis of Amino Acid Analogues: Structure and Functions

Sasmal, Supriya (2019) Synthesis of Amino Acid Analogues: Structure and Functions. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Supriya Sasmal (12IP003)) 12IP003.pdf - Submitted Version Restricted to Repository staff only Download (7MB)

Abstract

This thesis entitled “SYNTHESIS OF AMINO ACID ANALOGUES: STRUCTURE AND FUNCTIONS” discussed the design, synthesis, characterization, conformational analyses, selfassociation and application of small peptides using proteinus and / or noncoded amino acids. This thesis is divided into seven chapters. Chapter 1 reviews a general introduction of amino acids chemistry followed by the synthesis, characteristic and classification of diverse synthetic amino acids by different research groups across the world. Subsequently, it elaborates up to date works on the higher order assemblies of different amino acids to mimic common structural elements like supramolecular helices and β-sheets. The last portion of this chapter highlights the applications of synthetic amino acids in medicinal, biotechnological and material sciences. Chapter 2 describes the detail of synthetic strategy, experimental strategies and reagents that are employed to perform the whole thesis work. Chapter 3 represents the eco-friendly and facile synthetic protocol for the fabrication of welldecorated hydantoin derivatives on the surface of graphene oxide by sonication assisted exfoliation and assembly. The hydantoin derivatives were synthesized from urea and L-phenylalanine/Ltryptophan/ L-leucine by one-pot microwave-assisted solvent free synthesis. The X-ray crystallography shed some light on the structure and assembly pattern of the hydantoin derivatives. The formation of the hybrid materials were successfully characterized by AFM, FE-SEM, FT-IR, Raman, UV-vis and fluorescence spectroscopy. The resulted hybrid material acts as highly sensitive turn off guanine sensor. The approach and findings presented here could also be extended to the fabrication of sensors for other biologically active compounds. Chapter 4 represents design and synthesis of urea-modified tryptophan as in situ reducing and stabilizing agent for fabrication of gold nanoparticles in water. The tryptophan side chain NH has been used for reduction of gold ions in HAuCl4 to metallic gold and carboxylic acid functionality helps to stabilize the gold nanoparticles. This was confirmed by controlled reaction with urea-modified leucine which failed to form any gold nanoparticle. The resultant gold nanoparticles have been characterized by various spectroscopic techniques such as UV-visible spectroscopy, FT-IR spectroscopy and microscopic techniques such as FESEM and TEM. Moreover, the urea-modified tryptophan stabilized gold nanoparticles are catalyzing Suzuki- Miyaura cross-coupling reaction between the 4-bromobenzoic acid and phenylboronic acid in water provides 92% yield in 40 minutes. Chapter 5 described an efficient urea-modified -amino acids from amino acid by room-temperature treatment with KNCO. The single crystal X-ray study shows that the Leu containing urea-modified amino acid 1 forms a hydrogen-bonded honeycomb-like structure. But Arg containing urea-modified amino acid 2 forms a cage-like structure through water mediated intermolecular hydrogen bonding interactions. Out of 20 urea-modified amino acids, Arg, Pro, His and Gln containing compounds promote yeast growth significantly after 12 hours at pH 6.8 and 38°C. The compounds are not toxic. The Arg containing compound 2 shows two fold increase of yeast growth. However, the ureamodified m-aminobenzoic acid and p-aminobenzoic acid inhibits the yeast growth. NMR experiments confirmed the enhanced production of biofuel (EtOH) by glucose fermentation in presence of 2.5 mol compound 2. Not only glucose but also commercially available sugars exhibit significant production of biofuel under the same condition. Chapter 6 represents the correlation between molecular self-assembly pattern and optical behaviours. 4-biphenylcarboxy protected serine and tyrosine methyl esters were synthesized and their optical properties in solid state were investigated. The L-serine containing compound 1 exhibits green-gold birefringence under polarized light but the L-tyrosine containing compound 2 has no birefringence. Only compound 1 shows solid state emission at 525 nm. Irrespective of biphenyl chromophore, the compounds exhibit different packing-induced solid state optical properties. Chapter 7 discussed the synthesis of three diphenylalanine analogues by varying N-terminal protecting groups with Boc, acetyl, and 4-biphenylcarboxy groups. The solid-state structures show that the acetyl protected diphenylalanine adopts extended conformation and forms supramolecular helix like structure through multiple intermolecular hydrogen bonds. But, the 4-biphenylcarboxy protected diphenylalanine shows supramolecular sheet-like structure through intermolecular hydrogen bonds. From FESEM, depending on the N-terminal protecting groups, the compounds show nanotubes, nano rods and flakes like morphology. Moreover, only the 4-biphenylcarboxy protected diphenylalanine forms metalogel in presence of FeCl₃. A summary of the whole work is given after chapter 8. Chapters 3 to 7 begin with a short Introduction followed by Experimental Section, Results and Discussion, and Conclusion.

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