A novel nortriterpene, termed correolide, purified from the tree Spachea correae, inhibits Kv1.3, a Shaker-type delayed rectifier potassium channel present in human T lymphocytes. Correolide inhibits 86Rb+ efflux through Kv1.3 channels expressed in CHO cells (IC50 86 nM; Hill coefficient 1) and displays a defined structure-activity relationship. Potency in this assay increases with preincubation time and with time after channel opening. Correolide displays marked selectivity against numerous receptors and voltage- and ligand-gated ion channels. Although correolide is most potent as a Kv1.3 inhibitor, it blocks all other members of the Kv1 family with 4-14-fold lower potency. C20-29-[3H]dihydrocorreolide (diTC) was prepared and shown to bind in a specific, saturable, and reversible fashion (Kd = 11 nM) to a single class of sites in membranes prepared from CHO/Kv1.3 cells. The molecular pharmacology and stoichiometry of this binding reaction suggest that one diTC site is present per Kv1.3 channel tetramer. This site is allosterically coupled to peptide and potassium binding sites in the pore of the channel. DiTC binding to human brain synaptic membranes identifies channels composed of other Kv1 family members. Correolide depolarizes human T cells to the same extent as peptidyl inhibitors of Kv1.3, suggesting that it is a candidate for development as an immunosuppressant. Correolide is the first potent, small molecule inhibitor of Kv1 series channels to be identified from a natural product source and will be useful as a probe for studying potassium channel structure and the physiological role of such channels in target tissues of interest.

Two methods for the synthesis of vaulted biaryls were developed involving the reactions of carbene complexes with alkynes and the [2 + 2] cycloaddition of ketenes. The final step in the synthesis of 3,3‘-diphenyl-[2,2‘-binaphthalene]-1,1‘-diol (39) and 2,2‘-diphenyl-[3,3‘-biphenanthrene]-4,4‘-diol (47) (VAPOL) was phenol coupling of the 3-phenyl-1-naphthol (14) and the 2-phenyl-4-phenanthrol (28), respectively. The naphthol 14 could be prepared from the thermolysis of phenylacetyl chloride in the presence of phenylacetylene or from the benzannulation of the pentacarbonyl(phenylmethoxymethylene)chromium(0) (15) with phenylacetylene which upon an acetylative workup gives O-acetyl-4-methoxy-2-phenyl-1-naphthol (16). The reductive cleavage of the acetoxy group in 16 was unexpectedly affected by aluminum chloride and ethanethiol which were used to cleave the methyl ether. In a similar manner, the phenanthrol 28 could either be prepared from the 1-naphthylacetyl chloride (30) or pentacarbonyl(1-naphthylmethoxymethylene)chromium(0) (21). A new procedure for the preparation of carbene complexes was developed utilizing dimethyl sulfate as methylating agent. Unlike the benzannulation of the phenyl complex 15, the benzannulation of the naphthylcarbene complex 21 with phenylacetylene gave a side product which resulted from the incorporation of 2 equiv of the alkyne. This side product could be minimized by the proper control of the concentration of the alkyne. The phenol coupling of the 3-phenyl-1-naphthol with ferric chloride gave 2,2‘-diphenyl-[2,2‘-binaphthalene]-4,4‘-diol (38) and with air as oxidant gave the of 3,3‘-diphenyl-[2,2‘-binaphthalene]-1,1‘-diol (39). Oxidative coupling of the 2-phenyl-4-phenanthrol (28) with air gave 2,2‘-diphenyl-[3,3‘-biphenanthrene]-4,4‘-diol (47) (VAPOL), but the same coupling with 2-tert-butyl-4-phenanthrol (34) failed. The 2,2‘-binaphthol 39 was resolved via its cyclic diester with phosphoric acid by salt formation with (−)-brucine, and the 3,3‘-biphenanthrol 47 was resolved via its cyclic deiester with phosphoric acid (49) by salt formation with (−)-cinchonidine. The configuration of (−)-39 was shown to be S from an X-ray analysis of the brucine salt, and the configuration of (+)-47 was shown to be S from an X-ray analysis the amide (S,S)-54 derived from 49 and (S)-α-methylbenzylamine.

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The voltage-gated potassium channel, K(v)1.3, is a novel target for development of immunosuppressants. Using a functional (86)Rb(+) efflux assay, a new class of high-affinity K(v)1.3 inhibitors has been identified. The initial active in this series, 4-phenyl-4-[3-(2-methoxyphenyl)-3-oxo-2-azaprop-1-yl]cyclohexanone (PAC), which is representative of a disubstituted cyclohexyl (DSC) template, displays a K(i) of ca. 300 nM and a Hill coefficient near 2 in the flux assay and in voltage clamp recordings of K(v)1.3 channels in human T-lymphocytes. PAC displays excellent specificity as it only blocks members of the K(v)1 family of potassium channels but does not affect many other types of ion channels, receptors, or enzyme systems. Block of K(v)1.3 by DSC analogues occurs with a well-defined structure-activity relationship. Substitution at the C-1 ketone of PAC generates trans (down) and cis (up) isomer pairs. Whereas many DSC derivatives do not display selectivity in their interaction with different K(v)1.x channels, trans DSC derivatives distinguish between K(v)1.x channels based on their rates of C-type inactivation. DSC analogues reversibly inhibit the Ca(2+)-dependent pathway of T cell activation in in vitro assays. Together, these data suggest that DSC derivatives represent a new class of immunosuppressant agents and that specific interactions of trans DSC analogues with channel conformations related to C-type inactivation may permit development of selective K(v)1.3 channel inhibitors useful for the safe treatment of autoimmune diseases.

Antimicrobial resistance is a public health emergency and warrants coordinated global efforts. Challenge is that no alternative molecular platform has been identified for discovery of abundant antimicrobial hit compounds. Xanthene libraries have been screened for bioactive compounds. However, the potentially accessible chemistry space of xanthene dyes is limited by the existing xanthene synthesis. Herein we report a mild one-step synthesis, which permits late-stage introduction of a xanthene moiety onto i.e. natural products, pharmaceuticals, and bioactive compounds and construction of a focused library of rhodamine dyes exhibiting facile functional, topographical and stereochemical diversity. In vitro screening yields 37 analogs with mid-to-high bactericidal activity against WHO priority drug-resistant pathogens. These findings suggest that synthetic dye libraries exhibiting high structural diversity is a feasible chemical space combating antibacterial resistance, to complement the natural sources.

The first examples of the reactions of Fischer carbene complexes with 1,3-butadiynes are reported. These reactions are of interest since they provide new methods for the synthesis of acetylenic substituted arenes and also for the synthesis of biaryls. The reactions of the complexes (CO)5CrC(OR1)R2 [R1 = Me, n-Bu; R2 = phenyl, 1-naphthyl, 1-cyclohexenyl] were investigated with the conjugated diynes R3C⋮CC⋮CR3 [R3 = t-Bu, i-Pr, Ph]. All of the carbene complexes will react with 1 equiv of the diyne to give good yields of acetylenic arenes 5, 19, and 23, each with high selectivity for the regioisomer in which the substituent R3 on the diyne is incorporated adjacent to the phenol function. The reactions of the alkynylarenes 5, 19, and 23 with a second equivalent of carbene complexes, 4, 16, and 22, respectively, generate the bis-phenols 26, 31, and 33, with varying amounts of five-membered-ring annulated compounds as side products. These side products are not seen with the cyclohexenyl complex 22 and can be minimized to some extent for the phenyl complex 4a by proper control of the concentration and the temperature. Attempts to carry out benzannulations of both of the acetylenic functions in the 1,3-diyne concurrently by employing 2 equiv of the carbene complex were not successful, and this is suspected to be due to the presence of a chromium tricarbonyl group on the newly formed arene ring after the first benzannulation, such as in complex 34. The concurrent double benzannulation of a diyne can be achieved in an intramolecular fashion with the bis-carbene complex 39. The intramolecular process leads to a reversal in the regiochemistry of the second benzannulation producing the C 2-symmetrical 2,2‘-binaphthol 40 from the reaction of complex 39 with the diyne 8 along with the indenylnaphthalene 41. The reaction of the optically pure bis-carbene complex 44 derived from (2R,3R)-butane-2,3-diol with diyne 8 gives a single diastereomer of the 2,2‘-binaphthol 46. Chemical correlation with the known 2,2‘-binaphthol 51 reveals that the biaryl axis in 46 has an S-configuration, which was predicted from an examination of models.

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