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I. Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Erythromycin Derivatives. II. Algebraic Chemistry

Citation

Nourse, James Gregory (1974) I. Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Erythromycin Derivatives. II. Algebraic Chemistry. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/0vg4-h136. https://resolver.caltech.edu/CaltechTHESIS:06152021-231651716

Abstract

I. Carbon-13 Nuclear-Magnetic Resonance Spectroscopy of Erythromycin Derivatives

CMR spectra were taken and assigned for a series of erythromycin derivatives. Interpretation was based on known effects on cmr spectra and conformational changes among the derivatives. While the results were consistent with a gross conformational homogeneity, some subtle differences were observed. Proposals were made concerning the conformational differences between erythromycin A and Band among the series of aglycones. A conformation was proposed for 5,6-dideoxy-5-oxoerythronolide B consistent with cmr and pmr results. It was also proposed that in the natural antibiotics the desosamine side-chain sugar is free to swing around to the side of the aglycone ring, while the cladinose side-chain sugar is relatively fixed. The results suggested and were consistent with this situation. In this series it appeared that cmr was most useful in ascertaining intramolecular hydrogen bonding and orientation of and around carbonyls. Diagnostic usefulness for the various ketal structures was also suggested. The results of an enriched propionate feeding experiment confirmed the propionate biosynthesis hypothesis and gave direct evidence for the origin of the individual aglycone carbons.

II. Algebraic Chemistry

Several mathematical-chemical problems were treated and general considerations discussed.

It was shown that the Polya method could be used to count stereoisomers in systems with chiral ligands. An iterative procedure was given to determine the distribution and symmetry of all isomers possible in any given system. An extension of the method was made to count possible one-step substitution reactions in benzene systems.

The algebraic nature of the synthetic design problem was discussed, based on some simple concepts from algebraic topology. It was shown that the symmetry group of a chemical structure relevant to the synthetic design problem can be considerably larger than the usual point group. Examples of this group were constructed along with some methods for taking advantage of this symmetry in hypothetical cases.

A complete algebraic description of pseudochirality was given. It was shown that pseudochirality results when a structure lacks a particular kind of symmetry based on the point group and operations which invert configurations of chiral ligands. Other related forms of stereoisomerism were similarly described. A derivation of the possible pseudochirality groups based on the usual point groups was given.

The treatment of through-space orbital interactions given by Goldstein and Hoffmann was described abstractly and extended to reaction problems. A ribbon topology was assigned a homomorphism from a group of mode change operations to a group of interaction change operations. The concept of topologically equivalent transition state geometries was shown to correspond to group isomorphisms. The action of the mode. change group on a dynamic symmetry group for 1,5-hexadiene was given which interchanged allowed and forbidden reactions. It was suggested that the existence of allowed and forbidden reactions could be considered as a symmetry of a chemical structure.

The applicability of concepts of categorical algebra to biological, physical and chemical problems was discussed. Basic categorical concepts were discussed and it was shown that the center. and inner automorphism groups are functorial constructions on the subcategory of Grp including only epi arrows. General features of application of categorical concepts outside pure mathematics were compared. The functorial nature of the problems treated in earlier sections was discussed. The similarity between isomerization of triaryl methanes and tris-metal chelates observed by Gust and Mislow was expressed as an isomorphism of the dynamic symmetry groups. The use of groupoids in problems of isomerizations between different geometric forms was demonstrated. It was shown that groupoids can be considered as representations of wreath products. A dynamic symmetry group for cyclobutene-butadiene interconversions was derived.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Roberts, John D. (advisor)
  • Ireland, Robert E. (co-advisor)
Thesis Committee:
  • Roberts, John D. (chair)
  • Ireland, Robert E. (co-chair)
Defense Date:12 September 1973
Funders:
Funding AgencyGrant Number
CaltechUNSPECIFIED
NIHUNSPECIFIED
Record Number:CaltechTHESIS:06152021-231651716
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:06152021-231651716
DOI:10.7907/0vg4-h136
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14278
Collection:CaltechTHESIS
Deposited By: Benjamin Perez
Deposited On:22 Jun 2021 22:02
Last Modified:08 May 2024 17:04

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