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...
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 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...
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...
PART I. The preparation of (-)-ibogamine (1) in fourteen steps from benzoquinone and in 10% overall yield is a powerful illustration of the value of the asymmetric Diels-Alder reaction as a starting point in a multistep synthesis. All four cycloadducts, 70, 77, 84 and 96, obtained with the (S)-BINOL-TiCl₂ complex...
Various hypervalent iodine compounds were evaluated as reagents
for intramolecular phenolic oxidative coupling. It was found that
phenyliodine(III) bis(trifluoroacetate) was effective for the coupling
of the monophenolic substrate 13a to 14a under neutral conditions.
Vanadium oxytrifluoride and hypervalent iodine compounds were compared
as oxidants for the conversion of 32 to...
A convergent synthesis of epothilone B that generates all seven of its
asymmetric centers in a completely stereoselective fashion has been
completed. Key reactions include an anti-Felkin aldol condensation to
set the C6 and C7 stereochemistry, a directed α-hydroxylation to install
the C15 (S)-hydroxyl substituent, and a Wittig condensation to...
An asymmetric approach to the synthesis of byssochlamic acid (1) is
described. Regioisomeric enzymatic differentiation is described in the selective
hydrolysis of dimethyl ester 30 by porcine liver esterase. Chiral dimethyl ester 42
was prepared by desymmetrization of cyclopentene 34 using porcine liver
esterase. A key intramolecular [2+2]cycloaddition-cycloreversion
photometathesis of...
Irradiation of a tryptamine linked through its side-chain nitrogen to an alkylidene malonate residue results in an intramolecular [2 + 2] cycloaddition to the indole 2,3-double bond. The resultant cyclobutane undergoes spontaneous retro-Mannich fission to produce a spiro[indoline-3,3-pyrrolenine] with relative configuration defined by the orientation of substituents in the transient...
An approach to the generation of polyketides was investigated,
which involved ozonolysis of 6, 7 cyclopenteno -1> 4, 5, 8 -tetrahydromethoxy-
3-methylnaphthalene (26), to produce what is believed to be
polyketide 27. Compound 26 was formed by the following sequence:
Die ls -Alder addition of 1, 2 -dim.ethylenecyclopentane and 2...
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...