Graduate Thesis Or Dissertation
 

Synthesis of metabolites from the ascomycetes : I. The synthesis and absolute configuration of leptosphaerin : II. Approaches to the synthesis of byssochlamic acid

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bv73c3320

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  • Part I. The total synthesis of (+)-leptosphaerin (2), a metabolite of the marine Ascomycete Leptosphaeria Oraemaris (Linder) was achieved, unambiguously establishing both the relative and absolute stereochemistry of this natural product. This synthesis also resolved the long-standing question of which of the isomeric structures 1 or 2 correctly represents the structure of leptosphaerin. The target material was prepared in 12 steps, beginning from mannitol and ethyl pyruvate. In the key step a protected form of R-(+)-glyceraldehyde (3) underwent a stereospecific condensation with a 3- lithioacrylate derivative (48) to give a product (55) which was elaborated into leptosphaerin. The stereochemical outcome of this condensation was determined by means of a single crystal X-ray analysis. Part II. Two synthetic approaches to byssochlamic acid (3), a metabolite of Byssochlamys fulva, were studied. The first of these was based on a route in which a suitably functionalized 1,5-hexadiene (23) was intended to provide the substrate for an intramolecular [2+2] photocycloaddition. The impracticability of obtaining a suitable photolysis substrate caused revision of this strategy, for which the macrolide 88 became the focal intermediate. The bis phenol 89 was prepared by a sequence of reactions, the key step of which was the samarium diiodide mediated alkylation of 2',5'-dimethoxybutyrophenone (79) with 2,5-dimethoxybenzyl bromide (77). Reduction of the resulting tertiary alcohol (80) was followed by the selective protection of 80 as bisphenol 89, which underwent esterification with ethylmalonyl dichloride to give macrolide 88.
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