The ethyl acetate extract of the culture filtrate of the marine Ascomycete,
Leptosphaeria oraemaris (Linder) yielded a novel metabolite
designated by the common name leptosphaerin. An x-ray crystallographic
structure analysis was disproved by the synthesis of 3-acetoxy-S-(1,2-dihydroxyethyl)-
3-pyrrolin-2-one 1, starting with N,N-dibenzylhydroxylamine
47 and D-mannitol 44. Oxidation of 47 followed...
A total synthesis of the fungal hormones, trisporic acids A and B, is described, starting from a -methyltetronic acid 34. A Robinson annelation of 34 with ethyl vinyl ketone affords the lactone 33. Treatment of 33 with N-bromosuccinimide gave 97, which was hydrolyzed to the lactol 103. The reaction of...
Several approaches to the synthesis of penicillin from 2-iminothioazolidine
50, from 2-thiothiazolidine 66 and by photocyclization of
77 and 78 were investigated. 2-Iminothiazolidine 50 was prepared
from dibromoester 45 by the action of benzylamine followed by treatment
of aziridine 46 with potassium or ammonium thiocyanate. Attempted
introduction of a two-carbon...
Bromoalkoxylation of dihydropyran with bromine and 1-borneol, followed by dehydrobromination and epoxidation, afforded trans-2-1- bornyloxy-3,4-epoxytetrahydropyran as a major product. This was treated with sodium phenylselenide to give a 1:1 mixture of (2R,3R,4R)- 2-1-bornyloxy-3-hydroxy-4-phenylselenotetrahydropyran and its (2S,3S, 4S) diastereomer. Elimination of the selenoxide, derived from oxidation of the former with hydrogen...
The mycosporins, formerly called P310's are secondary metabolites
of fungi closely associated with fungal reproductive processes that
require light. The structurally related iminomycosporins are found in
marine plants and animals and may also have functions related to
light. In this study, approaches toward the asymmetric synthesis of
the mycosporins are...
The rearrangement of a homoallyl cation to a cyclopropylcarbinyl cation is thought to play a role in the biogenesis of a variety of cyclopropane-containing natural products,¹ a hypothesis which has previously led to the design of successful biomimetic syntheses of several natural products.² The strategy underlying this approach to cyclopropane...
Rapamycin (5) was isolated in 1975 from the soil bacteria Streptomyces hygroscopicus and its structure was determined from spectroscopic techniques and an x-ray crystallographic analysis. Although it was initially found to exhibit antibiotic activity, it was subsequently shown to possess potent immunosuppressive activity as well.
Three approaches to the synthesis...
This thesis describes the development of a new enantioselective synthetic method employing chiral cis-2,5-diaminobicyclo[2.2.2]octane-based organometallic catalysts. The significance of this new method to organic synthesis is illustrated with preparation of enantioenriched products that are transformed to important pharmaceutical agents. Chapter 1 provides a brief historical overview of asymmetric catalysis, especially...