dysiherbaine and Seizures

A rapid and efficient total synthesis of dysiherbaine (1), a potent and subtype-selective agonist for ionotropic glutamate receptors, has been accomplished. A key intermediate 15 was synthesized by two approaches. The first synthetic route utilized compound 9, an advanced intermediate in our previous total synthesis of neodysiherbaine A, as the starting point, and the cis-oriented amino alcohol functionality on the tetrahydropyran ring was installed by using an intramolecular S(N)2 cyclization of N-Boc-protected amino alcohol 20. An alternative and even more efficient synthetic approach to 15 featured stereoselective introduction of an amino group at C8 by iodoaminocyclization prior to constructing the bicyclic ether skeleton. The amino acid appendage was efficiently constructed by a catalytic asymmetric hydrogenation of enamide ester 36. The synthetic route developed here provided access to several dysiherbaine analogues, including 9-epi-dysiherbaine (38), 9-deoxydysiherbaine (39), 9-methoxydysiherbaine (40), and N-ethyldysiherbaine (41). The preliminary structure-activity relationship studies revealed that the presence and stereochemistry of the C9 hydroxy group in dysiherbaine is important for high-affinity and selective binding to glutamate subtype receptors.

Topics: Alanine; Animals; Bridged Bicyclo Compounds, Heterocyclic; Convulsants; Drug Evaluation, Preclinical; Injections, Intraventricular; Mice; Models, Molecular; Molecular Structure; Receptors, AMPA; Receptors, Kainic Acid; Seizures; Stereoisomerism; Structure-Activity Relationship

Dysiherbaine (1) and its congener neodysiherbaine A (2) are naturally occurring excitatory amino acids with selective and potent agonistic activity for ionotropic glutamate receptors. We describe herein the total synthesis of 2 and its structural analogues 3-8. Advanced key intermediate 16 was employed as a branching point to assemble a series of these analogues 3-8 with respect to the C8 and C9 functionalities, which would not have been accessible through manipulations of the natural product itself. The synthesis of key intermediate 16 features (i) stereocontrolled C-glycosylation to set the C6 stereocenter, (ii) concise synthesis of the bicyclic ether skeleton through chemo- and stereoselective dihydroxylation of the exo-olefin and stereoselective epoxidation of the endo-olefin, followed by epoxide ring opening/5-exo ring closure, and (iii) catalytic asymmetric hydrogenation of enamide ester to construct the amino acid appendage. A preliminary biological evaluation of analogues for their in vivo toxicity against mice and binding affinity for glutamate receptors showed that both the type and stereochemistry of the C8 and C9 functional groups affected the subtype selectivity of dysiherbaine analogues for members of the kainic acid receptor family.

Topics: Alanine; Animals; Binding, Competitive; Biological Assay; Bridged Bicyclo Compounds, Heterocyclic; Cell Line; Dose-Response Relationship, Drug; Humans; Injections, Intraventricular; Mice; Molecular Structure; Receptors, Kainic Acid; Seizures; Stereoisomerism; Structure-Activity Relationship

Dysiherbaine (DH) is a marine sponge-derived amino acid that causes seizures upon injection into mice. In this report we investigate the behavioral effects and characterize the pharmacological activity of DH. DH induced convulsive behaviors in mice with ED(50) values of 13 pmol/mouse, i.c.v. and 0.97 mg/kg, i.p. In rat brain synaptic membranes DH displaced binding of [3H]kainic acid (KA) and [3H]alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) with K(i) values of 26 and 153 nM, respectively; in contrast, DH did not displace the N-methyl-D-aspartic acid (NMDA) receptor ligand [3H]CGS-19755. DH displaced [3H]KA from recombinant GluR5 and GluR6 kainate receptor subunits expressed in HEK293 cells with K(i) values of 0.74 and 1.2 nM, respectively. In whole-cell voltage-clamp recordings from cultured rat hippocampal neurons, DH evoked inward currents from both AMPA and KA receptors with EC(50) values of 9.7 microM and 210 nM, respectively. AMPA receptor currents were blocked by GYKI 53655, whereas KA receptor currents were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Surprisingly, in calcium imaging experiments we found that DH also activated recombinant mGluR5 receptors but did not activate mGluR1 receptors. DH did not activate glutamate transporters or gamma-aminobutyric acid A (GABA(A)) receptors. These results indicate that DH is a potent non-NMDA-type agonist with very high affinity for KA receptors, as well as a subtype-selective mGluR agonist. DH possesses the most potent epileptogenic activity among the amino acids yet identified. This novel excitatory amino acid may prove useful for evaluating the physiological and pathological roles of non-NMDA receptors, especially KA receptors, in the central nervous system.

Topics: Alanine; Amino Acid Transport System X-AG; Animals; ATP-Binding Cassette Transporters; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Cells, Cultured; Convulsants; Diagnostic Imaging; Excitatory Amino Acid Agonists; In Vitro Techniques; Injections, Intraventricular; Male; Mice; Neurons; Porifera; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Seizures; Synaptic Membranes