Among the opioid receptors, the κ-opioid receptor (κOR) has been gaining considerable attention as a potential therapeutic target for the treatment of complex CNS disorders including depression, visceral pain, and cocaine addiction. With an interest in discovering novel ligands targeting κOR, we searched natural products for unusual scaffolds and identified collybolide (Colly), a nonnitrogenous sesquiterpene from the mushroom Collybia maculata. This compound has a furyl-δ-lactone core similar to that of Salvinorin A (Sal A), another natural product from the plant Salvia divinorum. Characterization of the molecular pharmacological properties reveals that Colly, like Sal A, is a highly potent and selective κOR agonist. However, the two compounds differ in certain signaling and behavioral properties. Colly exhibits 10-to 50-fold higher potency in activating the mitogen-activated protein kinase pathway compared with Sal A. Taken with the fact that the two compounds are equipotent for inhibiting adenylyl cyclase activity, these results suggest that Colly behaves as a biased agonist of κOR. Behavioral studies also support the biased agonistic activity of Colly in that it exhibits ∼10-fold higher potency in blocking non-histamine-mediated itch compared with Sal A, and this difference is not seen in pain attenuation by these two compounds. These results represent a rare example of functional selectivity by two natural products that act on the same receptor. The biased agonistic activity, along with an easily modifiable structure compared with Sal A, makes Colly an ideal candidate for the development of novel therapeutics targeting κOR with reduced side effects.G-protein-coupled receptors | natural compounds | salvinorin A | dynorphin | antinociception
MenE, the o-succinylbenzoate (OSB)-CoA synthetase from bacterial menaquinone biosynthesis, is a promising new antibacterial target. Sulfonyladenosine analogues of the cognate reaction intermediate, OSB-AMP, have been developed as inhibitors of the MenE enzymes from Mycobacterium tuberculosis (mtMenE), Staphylococcus aureus (saMenE) and Escherichia coli (ecMenE). Both a free carboxylate and ketone moiety on the OSB side chain are required for potent inhibitory activity. OSB-AMS (4) is a competitive inhibitor of mtMenE with respect to ATP (Ki = 5.4 ± 0.1 nM) and a non-competitive inhibitor with respect to OSB (Ki = 11.2 ± 0.9 nM). These data are consistent with a bi uni uni bi ping-pong kinetic mechanism for these enzymes. In addition, OSB-AMS inhibits saMenE with
Kiapp of 22 ± 8 nM and ecMenE with
KiOSB=128±5nM. Putative active site residues, Arg-222, which may interact with the OSB aromatic carboxylate, and Ser-302, which may bind the OSB ketone oxygen, have been identified through computational docking of OSB-AMP with the unliganded crystal structure of saMenE. A pH-dependent interconversion of the free keto acid and lactol forms of the inhibitors is also described, along with implications for inhibitor design.
The genesis and development of the 4,6-O-benzylidene acetal method for the preparation of β-mannopyranosides are reviewed. Particular emphasis is placed on the influence of the various protecting groups on stereoselectivity and these effects are interpreted in the framework of a general mechanistic scheme invoking a series of solvent-separated and contact ion pairs in dynamic equilibrium with a covalent α-glycosyl trifluoromethanesulfonate.
Natural
products and their derivatives continue to be wellsprings
of nascent therapeutic potential. However, many laboratories have
limited resources for biological evaluation, leaving their previously
isolated or synthesized compounds largely or completely untested.
To address this issue, the Canvass library of natural products was
assembled, in collaboration with academic and industry researchers,
for quantitative high-throughput screening (qHTS) across a diverse
set of cell-based and biochemical assays. Characterization of the
library in terms of physicochemical properties, structural diversity,
and similarity to compounds in publicly available libraries indicates
that the Canvass library contains many structural elements in common
with approved drugs. The assay data generated were analyzed using
a variety of quality control metrics, and the resultant assay profiles
were explored using statistical methods, such as clustering and compound
promiscuity analyses. Individual compounds were then sorted by structural
class and activity profiles. Differential behavior based on these
classifications, as well as noteworthy activities, are outlined herein.
One such highlight is the activity of (−)-2(S)-cathafoline, which was found to stabilize calcium levels in the
endoplasmic reticulum. The workflow described here illustrates a pilot
effort to broadly survey the biological potential of natural products
by utilizing the power of automation and high-throughput screening.
2,3-Di-O-benzyl-4,6-O-benzylidene-thiohexopyranosides, on activation with 1-benzenesulfinyl piperidine and triflic anhydride, react with allyl silanes and stannanes, and with silyl enolethers to give C-glycosides. In mannose the β-isomers are formed selectively whereas the glucose series provides the α-anomers. This selectivity pattern parallels that of O-glycoside formation and eliminates the need to consider donor-acceptor hydrogen bonding in the formation of the O-glycosides.
MenE is an o-succinylbenzoyl-CoA (OSB-CoA) synthetase in the bacterial menaquinone biosynthesis pathway and is a promising target for the development of novel antibacterial agents. The enzyme catalyzes CoA ligation via an acyl-adenylate intermediate, and we have previously reported tight-binding inhibitors of MenE based on stable acyl-sulfonyladenosine analogues of this intermediate, including OSB-AMS (1) which has an IC50 value of ≤ 25 nM for the Escherichia coli MenE. Herein, we show that OSB-AMS reduces menaquinone levels in S. aureus, consistent with its proposed mechanism of action, despite the observation that the antibacterial activity of OSB-AMS is ~1000-fold lower than the IC50 for enzyme inhibition. To inform the synthesis of MenE inhibitors with improved antibacterial activity, we have undertaken a structure–activity relationship (SAR) study stimulated by the knowledge that OSB-AMS can adopt two isomeric forms in which the OSB side chain exists either as an open-chain keto acid or a cyclic lactol. These studies revealed that negatively charged analogues of the keto-acid form bind, while neutral analogues do not, consistent with the hypothesis that the negatively-charged keto-acid form of OSB-AMS is the active isomer. X-ray crystallography and site-directed mutagenesis confirm the importance of a conserved arginine for binding the OSB carboxylate. Although most lactol isomers tested were inactive, a novel difluoroindanediol inhibitor (11) with improved antibacterial activity was discovered, providing a pathway toward the development of optimized MenE inhibitors in the future.
The Gram-negative bacterial pathogen Pseudomonas aeruginosa uses three interconnected intercellular
signaling systems regulated
by the transcription factors LasR, RhlR, and MvfR (PqsR), which mediate
bacterial cell–cell communication via small-molecule natural
products and control the production of a variety of virulence factors.
The MvfR system is activated by and controls the biosynthesis of the
quinolone quorum sensing factors HHQ and PQS. A key step in the biosynthesis
of these quinolones is catalyzed by the anthranilyl-CoA synthetase
PqsA. To develop inhibitors of PqsA as novel potential antivirulence
antibiotics, we report herein the design and synthesis of sulfonyladeonsine-based
mimics of the anthranilyl-AMP reaction intermediate that is bound
tightly by PqsA. Biochemical, microbiological, and pharmacological
studies identified two potent PqsA inhibitors, anthranilyl-AMS (1) and anthranilyl-AMSN (2), that decreased HHQ
and PQS production in P. aeruginosa strain
PA14. However, these compounds did not inhibit
production of the virulence factor pyocyanin. Moreover, they exhibited
limited bacterial penetration in compound accumulation studies. This
work provides the most potent PqsA inhibitors reported to date and
sets the stage for future efforts to develop analogues with improved
cellular activity to investigate further the complex relationships
between quinolone biosynthesis and virulence factor production in P. aeruginosa and the therapeutic potential of targeting
PqsA.
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