Enantioselective Total Synthesis of Blennolide†H and Phomopsis-H76†A and Determination of Their Structure.

This work reports on the enantioselective total synthesis of the two dimeric natural chromanone lactones phomopsis-H76 A (5) and blennolide H (6). Both syntheses could be achieved from chromane 11, which was obtained by an enantioselective Wacker-type cyclization with >99 % ee. The dimerization of the corresponding monomers was performed using a palladium-catalyzed Suzuki reaction. Moreover, within this work it was possible to revise the absolute configuration of phomopsis-H76 A and determine the relative as well as absolute configuration of blennolide H.

Enantioselective Total Synthesis and Structure Confirmation of the Natural Dimeric Tetrahydroxanthenone Dicerandrol†C.

The first enantioselective total synthesis of natural dicerandrol C (1 c) as its enantiomer containing a dimeric tetrahydroxanthenone skeleton is described starting from the enantiopure chromane 6 which was obtained through a Wacker-type cyclization with >99 % ee. For the formation of the dimeric skeleton a palladium-catalyzed Suzuki reaction was used. The synthesis allowed the confirmation of the absolute configuration of the dicerandrols.

Evaluation of a novel calcium channel agonist for therapeutic potential in Lambert-Eaton myasthenic syndrome.

We developed a novel calcium (Ca(2+)) channel agonist that is selective for N- and P/Q-type Ca(2+) channels, which are the Ca(2+) channels that regulate transmitter release at most synapses. We have shown that this new molecule (GV-58) slows the deactivation of channels, resulting in a large increase in presynaptic Ca(2+) entry during activity. GV-58 was developed as a modification of (R)-roscovitine, which was previously shown to be a Ca(2+) channel agonist, in addition to its known cyclin-dependent kinase activity. In comparison with the parent molecule, (R)-roscovitine, GV-58 has a ∼20-fold less potent cyclin-dependent kinase antagonist effect, a ∼3- to 4-fold more potent Ca(2+) channel agonist effect, and ∼4-fold higher efficacy as a Ca(2+) channel agonist. We have further evaluated GV-58 in a passive transfer mouse model of Lambert-Eaton myasthenic syndrome and have shown that weakened Lambert-Eaton myasthenic syndrome-model neuromuscular synapses are significantly strengthened following exposure to GV-58. This new Ca(2+) channel agonist has potential as a lead compound in the development of new therapeutic approaches to a variety of disorders that result in neuromuscular weakness.

Complete reversal of Lambert-Eaton myasthenic syndrome synaptic impairment by the combined use of a K+ channel blocker and a Ca2+ channel agonist.

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder in which a significant fraction of the presynaptic P/Q-type Ca(2+) channels critical to the triggering of neurotransmitter release at the neuromuscular junction (NMJ) are thought to be removed. There is no cure for LEMS, and the current most commonly used symptomatic treatment option is a potassium channel blocker [3,4-diaminopyridine (3,4-DAP)] that does not completely reverse symptoms and can have dose-limiting side-effects. We previously reported the development of a novel Ca(2+) channel agonist, GV-58, as a possible alternative treatment strategy for LEMS. In this study, we tested the hypothesis that the combination of GV-58 and 3,4-DAP will elicit a supra-additive increase in neurotransmitter release at LEMS model NMJs. First, we tested GV-58 in a cell survival assay to assess potential effects on cyclin-dependent kinases (Cdks) and showed that GV-58 did not affect cell survival at the relevant concentrations for Ca(2+) channel effects. Then, we examined the voltage dependence of GV-58 effects on Ca(2+) channels using patch clamp techniques; this showed the effects of GV-58 to be dependent upon Ca(2+) channel opening. Based on this mechanism, we predicted an interaction between 3,4-DAP and GV-58. We tested this hypothesis using a mouse passive transfer model of LEMS. Using intracellular electrophysiological ex vivo recordings, we demonstrated that a combined application of 3,4-DAP plus GV-58 had a supra-additive effect that completely reversed the deficit in neurotransmitter release magnitude at LEMS model NMJs. This reversal contrasts with the less significant improvement observed with either compound alone. Our data indicate that a combination of 3,4-DAP and GV-58 represents a promising treatment option for LEMS and potentially for other disorders of the NMJ.

Enantioselective Total Synthesis of Chromanone Lactone Homo- and Heterodimers.

A one pot borylation/Suzuki-Miyaura reaction of the 4-bromochromanone lactones 21 and 23, respectively, followed by cleavage of the methyl ether moieties gave the homodimeric chromanone lactones 10 and 11. Reaction of a 1:1 mixture of 21 and 23 under otherwise identical conditions gave a 1:1:2-mixture of the two homodimers 10 and 11 and the heterodimer 12. This is the first example of the preparation of a heterodimeric chromanone lactone. For the enantioselective synthesis of the starting material, phenol 17 was transformed into the chromane 18 using a Wacker-type cyclisation with 99 % ee and 80 % yield.

Enantioselective Total Synthesis of the Fungal Metabolite Blennolide D and the Enantiomers of Blennolide E and F.

An enantioselective total synthesis of blennolide D and the enantiomers of blennolide E and F is described using an enantioselective Wacker-type oxidation followed by the formation of the lactone moiety. For the introduction of the hydroxyl group in the γ-lactone, a TEMPO-mediated α-oxygenation was used which was followed by a benzylic oxidation and deprotection to give the desired compounds. In addition, an unknown diastereomer was synthesized.

Lambert-Eaton myasthenic syndrome: mouse passive-transfer model illuminates disease pathology and facilitates testing therapeutic leads.

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder caused by antibodies directed against the voltage-gated calcium channels that provide the calcium ion flux that triggers acetylcholine release at the neuromuscular junction. To study the pathophysiology of LEMS and test candidate therapeutic strategies, a passive-transfer animal model has been developed in mice, which can be created by daily intraperitoneal injections of LEMS patient serum or IgG into mice for 2-4 weeks. Results from studies of the mouse neuromuscular junction have revealed that each synapse has hundreds of transmitter release sites but that the probability for release at each one is likely to be low. LEMS further reduces this low probability such that transmission is no longer effective at triggering a muscle contraction. The LEMS-mediated attack reduces the number of presynaptic calcium channels, disorganizes transmitter release sites, and results in the homeostatic upregulation of other calcium channel types. Symptomatic treatment is focused on increasing the probability of release from dysfunctional release sites. Current treatment uses the potassium channel blocker 3,4-diaminopyridine (DAP) to broaden the presynaptic action potential, providing more time for calcium channels to open. Current research is focused on testing new calcium channel gating modifiers that work synergistically with DAP.

New calcium channel agonists as potential therapeutics in Lambert-Eaton myasthenic syndrome and other neuromuscular diseases.

Lambert-Eaton myasthenic syndrome (LEMS) causes neuromuscular weakness as a result of an autoimmune attack on the calcium channels that normally regulate chemical transmitter release at the neuromuscular junction. Currently there are limited treatment options for patients with this and other forms of neuromuscular weakness. A novel, first-in-class calcium channel agonist that is selective for the types of voltage-gated calcium channels that regulate transmitter release at neuromuscular synapses has recently been developed. This compound (GV-58) slows deactivation (closing) of the channel, resulting in a large increase in total calcium entry during motor nerve action potential activity. This new calcium channel agonist is currently being evaluated for the treatment of neuromuscular weakness. Potential applications include development as single therapeutics, or for combination treatments.

Synthesis and biological evaluation of a selective N- and p/q-type calcium channel agonist.

The acute effect of the potent cyclin-dependent kinase (cdk) inhibitor (R)-roscovitine on Ca(2+) channels inspired the development of structural analogues as a potential treatment for motor nerve terminal dysfunction. On the basis of a versatile chlorinated purine scaffold, we have synthesized ca. 20 derivatives and characterized their N-type Ca(2+) channel agonist action. Agents that showed strong agonist effects were also characterized in a kinase panel for their off-target effects. Among several novel compounds with diminished cdk activity, we identified a new lead structure with a 4-fold improved N-type Ca(2+) channel agonist effect and a 22-fold decreased cdk2 activity as compared to (R)-roscovitine. This compound was selective for agonist activity on N- and P/Q-type over L-type calcium channels.