The details of the
total synthesis of viridicatumtoxin B (1) are described.
Initial synthetic strategies toward this
intriguing tetracycline antibiotic resulted in the development of
key alkylation and Lewis acid-mediated spirocyclization reactions
to form the hindered EF spirojunction, as well as Michael–Dieckmann
reactions to set the A and C rings. The use of an aromatic A-ring
substrate, however, was found to be unsuitable for the introduction
of the requisite hydroxyl groups at carbons 4a and 12a. Applying these
previous tactics, we developed stepwise approaches to oxidize carbons
12a and 4a based on enol- and enolate-based oxidations, respectively,
the latter of which was accomplished after systematic investigations
that revealed critical reactivity patterns. The herein described synthetic
strategy resulted in the total synthesis of viridicatumtoxin B (1), which, in turn, formed the basis for the revision of its
originally assigned structure. The developed chemistry facilitated
the synthesis of a series of viridicatumtoxin analogues, which were
evaluated against Gram-positive and Gram-negative bacterial strains,
including drug-resistant pathogens, revealing the first structure–activity
relationships within this structural type.
Will the real viridicatumtoxin B please stand up
Total synthesis of viridicatumtoxin B resulted in its structural revision and opens the way for analogue construction and biological evaluation of this complex tetracycline antibiotic. The highly convergent strategy employed allows for swift construction of the entire carbocyclic framework of the molecule.
A catalytic asymmetric total synthesis of the potent and selective antileukemic Δ12-prostaglandin J3 (Δ12-PGJ3) is described. The convergent synthesis proceeded through intermediates 2 and 3, constructed enantioselectively from readily available starting materials and coupled through an aldol reaction followed by dehydration to afford stereoselectively the cyclopentenone alkylidene structural motif of the molecule.
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