Stereochemistry and innate immune recognition: (+)-norbinaltorphimine targets myeloid differentiation protein 2 and inhibits toll-like receptor 4 signaling.

Deregulation of innate immune TLR4 signaling contributes to various diseases including neuropathic pain and drug addiction. Naltrexone is one of the rare TLR4 antagonists with good blood-brain barrier permeability and showing no stereoselectivity for TLR4. By linking 2 naltrexone units through a rigid pyrrole spacer, the bivalent ligand norbinaltorphimine was formed. Interestingly, (+)-norbinaltorphimine [(+)-1] showed ∼25 times better TLR4 antagonist activity than naltrexone in microglial BV-2 cell line, whereas (-)-norbinaltorphimine [(-)-1] lost TLR4 activity. The enantioselectivity of norbinaltorphimine was further confirmed in primary microglia, astrocytes, and macrophages. The activities of meso isomer of norbinaltorphimine and the molecular dynamic simulation results demonstrate that the stereochemistry of (+)-1 is derived from the (+)-naltrexone pharmacophore. Moreover, (+)-1 significantly increased and prolonged morphine analgesia in vivo. The efficacy of (+)-1 is long lasting. This is the first report showing enantioselective modulation of the innate immune TLR signaling.-Zhang, X., Peng, Y., Grace, P. M., Metcalf, M. D., Kwilasz, A. J., Wang, Y., Zhang, T., Wu, S., Selfridge, B. R., Portoghese, P. S., Rice, K. C., Watkins, L. R., Hutchinson, M. R., Wang, X. Stereochemistry and innate immune recognition: (+)-norbinaltorphimine targets myeloid differentiation protein 2 and inhibits toll-like receptor 4 signaling.

Mathematical and Structural Characterization of Strong Nonadditive Structure-Activity Relationship Caused by Protein Conformational Changes.

In medicinal chemistry, accurate prediction of additivity-based structure-activity relationship (SAR) analysis rests on three assumptions: (1) a consistent binding pose of the central scaffold, (2) no interaction between the R group substituents, and (3) a relatively rigid binding pocket in which the R group substituents act independently. Previously, examples of nonadditive SAR have been documented in systems that deviate from the first two assumptions. Local protein structural change upon ligand binding, through induced fit or conformational selection, although a well-known phenomenon that invalidates the third assumption, has not been linked to nonadditive SAR conclusively. Here, for the first time, we present clear structural evidence that the formation of a hydrophobic pocket upon ligand binding in PDE2 catalytic site reduces the size of another distinct subpocket and contributes to strong nonadditive SAR between two otherwise distant R groups.

Structure-Activity Relationships of (+)-Naltrexone-Inspired Toll-like Receptor 4 (TLR4) Antagonists.

Activation of Toll-like receptors has been linked to neuropathic pain and opioid dependence. (+)-Naltrexone acts as a Toll-like receptor 4 (TLR4) antagonist and has been shown to reverse neuropathic pain in rat studies. We designed and synthesized compounds based on (+)-naltrexone and (+)-noroxymorphone and evaluated their TLR4 antagonist activities by their effects on inhibiting lipopolysaccharide (LPS) induced TLR4 downstream nitric oxide (NO) production in microglia BV-2 cells. Alteration of the N-substituent in (+)-noroxymorphone gave us a potent TLR4 antagonist. The most promising analog, (+)-N-phenethylnoroxymorphone ((4S,4aR,7aS,12bR)-4a,9-dihydroxy-3-phenethyl-2,3,4,4a,5,6-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinolin-7(7aH)-one, 1j) showed ∼75 times better TLR-4 antagonist activity than (+)-naltrexone, and the ratio of its cell viability IC50, a measure of its toxicity, to TLR-4 antagonist activity (140 µM/1.4 µM) was among the best of the new analogs. This compound (1j) was active in vivo; it significantly increased and prolonged morphine analgesia.

Synthesis of enantiopure 10-nornaltrexones in the search for Toll-like receptor 4 antagonists and opioid ligands.

10-Nornaltrexones (3-(cyclopropylmethyl)-4a,9-dihydroxy-2,3,4,4a,5,6-hexahydro-1H-benzofuro[3,2-e]isoquinolin-7(7aH)-one, 1) have been underexploited in the search for better opioid ligands, and their enantiomers have been unexplored. The synthesis of trans-isoquinolinone 2 (4-aH, 9-O-trans-9-methoxy-3-methyl-2,3,4,4a,5,6-hexahydro-1H-benzofuro[3,2-e]isoquinolin-7(7aH)-one) was achieved through a nonchromatographic optimized synthesis of the intermediate pyridinyl compound 12. Optical resolution was carried out on 2, and each of the enantiomers were used in efficient syntheses of the "unnatural" 4aR,7aS,12bR-(+)-1) and its "natural" enantiomer (-)-1. Addition of a 14-hydroxy (the 4a-hydroxy) group in the enantiomeric isoquinolinones, (+)- and (-)-2), gave (+)- and (-)-10-nornaltrexones. A structurally unique tetracyclic enamine, (12bR)-7,9-dimethoxy-3-methyl-1,2,3,7-tetrahydro-7,12b-methanobenzo[2,3]oxocino[5,4-c]pyridine, was found as a byproduct in the syntheses and offers a different opioid-like skeleton for future study.

Synthesis studies on the lomaiviticin A aglycone core: development of a divergent, two-directional strategy.

The enantiomer of the bicyclic lomaiviticin aglycone A core was prepared via a two-directional, divergent approach featuring (1) a double Ireland Claisen rearrangement to establish key core bonds with correct relative stereochemistry and (2) a double olefin metathesis reaction to deliver both cyclohexene rings of the target.

Enantioselective synthesis of the ent-lomaiviticin A bicyclic core.

The bicyclic core of ent-lomaiviticin A was prepared in 11 operations from (S)-1-phenyl-2-propyn-1-ol in a two-directional route that features (1) a double Ireland Claisen rearrangement and (2) a double olefin metathesis reaction to form the key C-C bonds of the target.

EXPLORATION OF BRAVERMAN REACTION CHEMISTRY. SYNTHESIS OF TRICYCLIC DIHYDROTHIOPHENE DIOXIDE DERIVATIVES FROM BISPROPARGYL SULFONES.

The base-mediated bicyclization of unsymmetrical bispropargyl sulfones furnishes varying yields of dihydroisobenzothiophene dioxides through a presumed diradical intermediate. Attempts to trap a putative thiophene dioxide intermediate via Diels-Alder reaction with a pendant alkyne were not successful.