9 research outputs found
Studies toward the Unique Pederin Family Member Psymberin: Full Structure Elucidation, Two Alternative Total Syntheses, and Analogs
Two synthetic approaches to psymberin have been accomplished.
A
highly convergent first generation synthesis led to the complete stereochemical
assignment and demonstrated that psymberin and irciniastatin A are
identical compounds. This synthesis featured a diastereoselective
aldol coupling between the aryl fragment and a central tetrahydropyran
core and a novel one-pot procedure to convert an amide, via intermediacy
of a sensitive methyl imidate, to the <i>N</i>-acyl aminal
reminiscent of psymberin. The highlights of the second generation
synthesis include an efficient iridium-catalyzed enantioselective
bisallylation of neopentyl glycol and a stepwise Sonogashira coupling/cycloisomerization/reduction
sequence to construct the dihydroisocoumarin unit. The two synthetic
avenues were achieved in 17â18 steps (longest linear sequence,
âŒ14â15 isolations) from 3 fragments prepared in 7â8
(first generation) and 3â8 (second generation) steps each.
This convergent approach allowed for the preparation of sufficient
amounts of psymberin (⌠0.5 g) for follow-up biological studies.
Meanwhile, our highly flexible strategy enabled the design and synthesis
of multiple analogs, including a psymberinâpederin hybrid,
termed psympederin, that proved crucial to a comprehensive understanding
of the chemical biology of psymberin and related compounds that will
be described in a subsequent manuscript
Rifamycin Biosynthetic Congeners: Isolation and Total Synthesis of Rifsaliniketal and Total Synthesis of Salinisporamycin and Saliniketals A and B
We describe the isolation,
structure elucidation, and total synthesis
of the novel marine natural product rifsaliniketal and the total synthesis
of the structurally related variants salinisporamycin and saliniketals
A and B. Rifsaliniketal was previously proposed, but not observed,
as a diverted metabolite from a biosynthetic precursor to rifamycin
S. Decarboxylation of rifamycin provides salinisporamycin, which upon
truncation with loss of the naphthoquinone ring leads to saliniketals.
Our synthetic strategy hinged upon a PtÂ(II)-catalyzed cycloisomerization
of an alkynediol to set the dioxabicyclo[3.2.1]Âoctane ring system
and a fragmentation of an intermediate dihydropyranone to forge a
stereochemically defined (<i>E</i>,<i>Z</i>)-dienamide
unit. Multiple routes were explored to assemble fragments with high
stereocontrol, an exercise that provided additional insights into
acyclic stereocontrol during stereochemically complex fragment-assembly
processes. The resulting 11â14 step synthesis of saliniketals
then enabled us to explore strategies for the synthesis and coupling
of highly substituted naphthoquinones or the corresponding naphthalene
fragments. Whereas direct coupling with naphthoquinone fragments proved
unsuccessful, both amidation and CâN bond formation tactics
with the more electron-rich naphthalene congeners provided an efficient
means to complete the first total synthesis of rifsaliniketal and
salinisporamycin
Studies toward the Unique Pederin Family Member Psymberin: StructureâActivity Relationships, Biochemical Studies, and Genetics Identify the Mode-of-Action of Psymberin
Psymberin is the only member of the pederin natural product
family
that contains a dihydroisocoumarin side chain. Structural modifications
of psymberin uncoupled inhibition of protein translation from cytotoxicity,
suggesting that psymberin has more than one bioactivity. A forward
genetic screen in Caenorhabditis elegans was conducted to identify the molecular target(s) of psymberin.
Multiple independent psymberin-resistant mutants were isolated, each
containing the same point mutation in a gene encoding a ribosomal
protein. However, a psymberin-resistant mutant strain bearing this
mutation was not cross-resistant to the pederin family member mycalamide
A, which binds to the archaeal form of the same protein. Thus, two
pederin family members likely differ in how they bind the same molecular
target. The accumulation of psymberin in cells was sensitive to the
stereochemistry of the amide side chain at C4 or C8 and the presence
of the dihydroisocoumarin side chain. The observation that psymberin
diastereomers or dihydroisocoumarin-truncated analogs lose all cytotoxic
activity while retaining the ability to inhibit protein translation
in a cell-free in vitro assay can be explained in the context of these
differential cell uptake issues. Finally, we also demonstrate that
the blistering activity associated with pederin and other members
of the family is not due to their protein synthesis inhibiting activity.
Unlike pederin and mycalamide, psymberin does not display irritant
or blistering activity
SAR-Based Optimization of a 4âQuinoline Carboxylic Acid Analogue with Potent Antiviral Activity
It is established that drugs targeting
viral proteins are at risk
of generating resistant strains. However, drugs targeting host factors
can potentially avoid this problem. Herein, we report structureâactivity
relationship studies leading to the discovery of a very potent lead
compound 6-fluoro-2-(5-isopropyl-2-methyl-4-phenoxyphenyl)Âquinoline-4-carboxylic
acid (<b>C44</b>) that inhibits human dihydroorotate dehydrogenase
(DHODH) with an IC<sub>50</sub> of 1 nM and viral replication of VSV
and WSN-Influenza with an EC<sub>50</sub> of 2 nM and 41 nM. We also
solved the X-ray structure of human DHODH bound to <b>C44</b>, providing structural insight into the potent inhibition of biaryl
ether analogues of brequinar
Species-Selective Pyrimidineamine Inhibitors of <i>Trypanosoma brucei S</i>-Adenosylmethionine Decarboxylase
New therapeutic options are needed
for treatment of human African
trypanosomiasis (HAT) caused by protozoan parasite <i>Trypanosoma
brucei</i>. <i>S</i>-Adenosylmethionine decarboxylase
(AdoMetDC) is an essential enzyme in the polyamine pathway of <i>T. brucei</i>. Previous attempts to target this enzyme were
thwarted by the lack of brain penetration of the most advanced series.
Herein, we describe a <i>T. brucei</i> AdoMetDC inhibitor
series based on a pyrimidineamine pharmacophore that we identified
by target-based high-throughput screening. The pyrimidineamines showed
selectivity for <i>T. brucei</i> AdoMetDC over the human
enzyme, inhibited parasite growth in whole-cell assay, and had good
predicted bloodâbrain barrier penetration. The medicinal chemistry
program elucidated structureâactivity relationships within
the series. Features of the series that were required for binding
were revealed by determining the X-ray crystal structure of <i>Tb</i>AdoMetDC bound to one analog. The pyrimidineamine series
provides a novel starting point for an anti-HAT lead optimization
Species-Selective Pyrimidineamine Inhibitors of <i>Trypanosoma brucei S</i>-Adenosylmethionine Decarboxylase
New therapeutic options are needed
for treatment of human African
trypanosomiasis (HAT) caused by protozoan parasite <i>Trypanosoma
brucei</i>. <i>S</i>-Adenosylmethionine decarboxylase
(AdoMetDC) is an essential enzyme in the polyamine pathway of <i>T. brucei</i>. Previous attempts to target this enzyme were
thwarted by the lack of brain penetration of the most advanced series.
Herein, we describe a <i>T. brucei</i> AdoMetDC inhibitor
series based on a pyrimidineamine pharmacophore that we identified
by target-based high-throughput screening. The pyrimidineamines showed
selectivity for <i>T. brucei</i> AdoMetDC over the human
enzyme, inhibited parasite growth in whole-cell assay, and had good
predicted bloodâbrain barrier penetration. The medicinal chemistry
program elucidated structureâactivity relationships within
the series. Features of the series that were required for binding
were revealed by determining the X-ray crystal structure of <i>Tb</i>AdoMetDC bound to one analog. The pyrimidineamine series
provides a novel starting point for an anti-HAT lead optimization
Species-Selective Pyrimidineamine Inhibitors of <i>Trypanosoma brucei S</i>-Adenosylmethionine Decarboxylase
New therapeutic options are needed
for treatment of human African
trypanosomiasis (HAT) caused by protozoan parasite <i>Trypanosoma
brucei</i>. <i>S</i>-Adenosylmethionine decarboxylase
(AdoMetDC) is an essential enzyme in the polyamine pathway of <i>T. brucei</i>. Previous attempts to target this enzyme were
thwarted by the lack of brain penetration of the most advanced series.
Herein, we describe a <i>T. brucei</i> AdoMetDC inhibitor
series based on a pyrimidineamine pharmacophore that we identified
by target-based high-throughput screening. The pyrimidineamines showed
selectivity for <i>T. brucei</i> AdoMetDC over the human
enzyme, inhibited parasite growth in whole-cell assay, and had good
predicted bloodâbrain barrier penetration. The medicinal chemistry
program elucidated structureâactivity relationships within
the series. Features of the series that were required for binding
were revealed by determining the X-ray crystal structure of <i>Tb</i>AdoMetDC bound to one analog. The pyrimidineamine series
provides a novel starting point for an anti-HAT lead optimization
Inhibition of Influenza A Virus Infection <i>in Vitro</i> by Saliphenylhalamide-Loaded Porous Silicon Nanoparticles
Influenza A viruses (IAVs) cause recurrent epidemics in humans, with serious threat of lethal worldwide pandemics. The occurrence of antiviral-resistant virus strains and the emergence of highly pathogenic influenza viruses have triggered an urgent need to develop new anti-IAV treatments. One compound found to inhibit IAV, and other virus infections, is saliphenylhalamide (SaliPhe). SaliPhe targets host vacuolar-ATPase and inhibits acidification of endosomes, a process needed for productive virus infection. The major obstacle for the further development of SaliPhe as antiviral drug has been its poor solubility. Here, we investigated the possibility to increase SaliPhe solubility by loading the compound in thermally hydrocarbonized porous silicon (THCPSi) nanoparticles. SaliPhe-loaded nanoparticles were further investigated for the ability to inhibit influenza A infection in human retinal pigment epithelium and Madin-Darby canine kidney cells, and we show that upon release from THCPSi, SaliPhe inhibited IAV infection <i>in vitro</i> and reduced the amount of progeny virus in IAV-infected cells. Overall, the PSi-based nanosystem exhibited increased dissolution of the investigated anti-IAV drug SaliPhe and displayed excellent <i>in vitro</i> stability, low cytotoxicity, and remarkable reduction of viral load in the absence of organic solvents. This proof-of-principle study indicates that PSi nanoparticles could be used for efficient delivery of antivirals to infected cells
Identification of Trypanosoma brucei AdoMetDC Inhibitors Using a High-Throughput Mass Spectrometry-Based Assay
Human
African trypanosomiasis (HAT) is a fatal infectious disease caused
by the eukaryotic pathogen Trypanosoma brucei (<i>Tb</i>). Available treatments are difficult to administer
and have significant safety issues. <i>S</i>-Adenosylmethionine
decarboxylase (AdoMetDC) is an essential enzyme in the parasite polyamine
biosynthetic pathway. Previous attempts to develop <i>Tb</i>AdoMetDC inhibitors into anti-HAT therapies failed due to poor brain
exposure. Here, we describe a large screening campaign of two small-molecule
libraries (âŒ400,000 compounds) employing a new high-throughput
(âŒ7 s per sample) mass spectrometry-based assay for AdoMetDC
activity. As a result of primary screening, followed by hit confirmation
and validation, we identified 13 new classes of reversible <i>Tb</i>AdoMetDC inhibitors with low-micromolar potency (IC<sub>50</sub>) against both <i>Tb</i>AdoMetDC and <i>T. brucei</i> parasite cells. The majority of these compounds were >10-fold
selective against the human enzyme. Importantly, compounds from four
classes demonstrated high propensity to cross the bloodâbrain
barrier in a cell monolayer assay. Biochemical analysis demonstrated
that compounds from eight classes inhibited intracellular <i>Tb</i>AdoMetDC in the parasite, although evidence for a secondary
off-target component was also present. The discovery of several new <i>Tb</i>AdoMetDC inhibitor chemotypes provides new hits for lead
optimization programs aimed to deliver a novel treatment for HAT