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Access Type

WSU Access

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

David Crich

Abstract

AGAs are clinically important antibacterials for human therapy and have long been used as highly potent antibiotics for treating several bacterial infections. The fidelity of protein synthesis is affected by AGAs in the course of binding to specific sites of the bacterial rRNA. The clinical use of AGAs and their applications as therapeutics is restricted by toxicity (irreversible ototoxicity and reversible nephrotoxicity) and by the resistance of pathogens. The objective of this research was the development of proficient AGAs that are less toxic (i.e., more selective) and that evade resistance. The first three chapters of this thesis are aimed towards developing new aminoglycoside antibiotics with the emphasis on their chemical synthesis, and the biological evaluation of newly synthesized analogues, as well as the exploration of structure-activity relationships to understand the mechanism of their antimicrobial activity. In particular, studies have focused on the modification of the aminoglycosides apramycin and paromomycin so as to develop the next generation of potent AGAs.

Chapter two reveals the importance of the 6' and N7' positions of the apramycin by investigation of the antibacterial activity and antiribosomal activity of the ten apramycin derivatives which were synthesized by modifying these locations. The effect of such modifications on antiribosomal activity is discussed in terms of their influence on drug binding to specific residues in the decoding A site. This information is useful in the development of a structure activity relationship for the antibacterial activity of the apramycin class of aminoglycosides and will also assist in the future design and development of more active and less toxic aminoglycoside antibiotics.

Chapter three describes the structure-based design of an improved paromomycin derivative which carries an apramycin-like bicyclic ring I and a conformationally restricted hydroxyl or amine functionality. The influence of the bicyclic paromomycin 6'-hydroxy or amine groups on the binding pattern between AGA and bacterial RNA was investigated by using cell free translational assays. It was found that the bicyclic paromomycin derivative 155 with the equatorial 6’-hydroxy group has a better activity profile than parent paromomycin.

In chapter four, an efficient sialyl donor was developed for the challenging α-sialylation by means of a highly electron withdrawing isothiocyanato group incorporated at C-5 position sialic acid. The isothiocyanato sialyl donor 218 proved to be an excellent α-directing group in sialylation for a wide range of acceptors, and provided high yields. Further, the sialylation of corresponding sialyl phosphate donor 231 was also demonstrated to give excellent selectivity, but yields are lower due to competing elimination. In addition, the rich chemistry of isothiocyanate functionality is explored to introduce a variety of novel functionalities at the 5-position of the sialosides including deamination, an alkyl chain, various amides, and guanidine derivatives.

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