University of Illinois Urbana-Champaign

Structure and Biosynthesis of the Diterpene Hydrocarbon, Casbene

Guilford, William Joseph

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https://hdl.handle.net/2142/70182

Description

Title
Structure and Biosynthesis of the Diterpene Hydrocarbon, Casbene
Author(s)
Guilford, William Joseph
Issue Date
1982
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Abstract
  • The stereochemical course of the enzyme catalyzed cyclization of geranylgeranyl pyrophosphate (GGOPP) to casbene, (1S,14R)-(E,E,E)-3,7,11,15,15-pentamethylbicyclo{14.1.0}pentadeca-2,6,10-triene, was defined in the castor bean plant (Ricinus communis L.,) by resolving the four stereochemical ambiguities in the cyclization. The stereochemical course of the cyclization is defined as follows: (1) the re face of the C-14 carbon of GGOPP is attacked by the C-1 carbon, (2) the E geometry of the double bonds of GGOPP is retained in casbene, (3) the pro-S hydrogen is removed from the C-1 carbon of GGOPP, and (4) the configuration of the 14,15-double bond of GGOPP is retained in the cyclopropane ring of casbene.
  • The stereospecific loss of the pro-S hydrogen of GGOPP was assigned by determining the deuterium content of casbene biosynthesized in microgram quantities from (R,S)-GGOPP-1-d-1-t and (S)-GGOPP-1-d-1-t in the cell-free enzyme extract obtained from 3-day old castor bean seedlings. The analysis was carried out by GC-MS using selective ion monitoring.
  • The retention of the geometry of the four double bonds of GGOPP in the three double bonds and on the cyclopropane ring of casbene was assigned by analyzing the carbon-13 NMR spectrum of casbene labeled specifically with four carbon-13 atoms. The carbon-13 labeled casbenes were biosynthesized in submilligram amounts from three specifically labeled mevalonolactones which label the allylic carbons of GGOPP regiospecifically.
  • The re attack on the C-14 carbon center was determined by assigning the absolute configuration of casbene. The configuration was determined by oxidatively degrading casbene on a submilligram scale and identifying the degradation product as methyl (1S,3R)-2,2-dimethyl-3-(3-oxobutyl)cyclopropanecarboxylate by comparing the proton NMR spectra of the degradation product and authentic samples taken in the chiral solution: (R)-(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol in benzene-d(,6).
  • Interestingly, the stereochemical results of this study are identical with those observed in the formation of presqualene pyrophosphate from two farnesyl pyrophosphates and neither cyclization shows a primary deuterium isotope effect.
Graduation Semester
1982
Type of Resource
text
Permalink
http://hdl.handle.net/2142/70182

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