1
|
Hager A, Vrielink N, Hager D, Lefranc J, Trauner D. Synthetic approaches towards alkaloids bearing α-tertiary amines. Nat Prod Rep 2015; 33:491-522. [PMID: 26621771 DOI: 10.1039/c5np00096c] [Citation(s) in RCA: 134] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Alkaloids account for some of the most beautiful and biologically active natural products. Although they are usually classified along biosynthetic criteria, they can also be categorized according to certain structural motifs. Amongst these, the α-tertiary amine (ATA), i.e. a tetrasubstituted carbon atom surrounded by three carbons and one nitrogen, is particularly interesting. A limited number of methods have been described to access this functional group and fewer still are commonly used in synthesis. Herein, we review some approaches to asymmetrically access ATAs and provide an overview of alkaloid total syntheses where those have been employed.
Collapse
Affiliation(s)
- Anastasia Hager
- Fakultät für Chemie und Pharmazie, Ludwig-Maximilians-Universität München, and Munich Center for Integrated Protein Science, Butenandtstr. 5 - 13, 81377 München, Germany.
| | | | | | | | | |
Collapse
|
2
|
Moczydlowski EG. The molecular mystique of tetrodotoxin. Toxicon 2012; 63:165-83. [PMID: 23261990 DOI: 10.1016/j.toxicon.2012.11.026] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Accepted: 11/30/2012] [Indexed: 01/06/2023]
Abstract
In many respects tetrodotoxin (TTX) is the quintessential natural toxin. It is unequivocally toxic to mammals with LD(50) values for mice in the range of 10 μg/kg (intraperitoneal), 16 μg/kg (subcutaneous), and 332 μg/kg (oral) (Kao, 1966). Its biothreat status is recognized by its listing as a "Select Agent" by the US Department of Health and Human Services which includes regulated agents "determined to have the potential to pose a severe threat to both human and animal health" (http://www.selectagents.gov/). It has a well-defined cellular target (i.e., NaV channels) and pharmacological mode of action (i.e., block of nerve and muscle action potentials), and it is an indispensable chemical tool in neuroscience. It is widely distributed in marine and terrestrial ecosystems where it plays a role in the chemical ecology of predator-prey relationships and drives evolutionary selection of TTX-resistance (Hanifin, 2010; Williams, 2010; Zimmer and Ferrer, 2007). Lastly, TTX has acquired a certain mystique in scientific lore attributable to many fascinating aspects of its natural history and molecular interactions as presented in selected summary below. Additional information may be found in other excellent reviews (Fozzard and Lipkind, 2010; Kao, 1966; Lee and Ruben, 2008; Narahashi, 2001, 2008).
Collapse
Affiliation(s)
- Edward G Moczydlowski
- Nanobiology, Sandia National Laboratories, P.O. Box 5800, MS1413, Albuquerque, NM 87185-1413, USA
| |
Collapse
|
3
|
Zhang MM, McArthur JR, Azam L, Bulaj G, Olivera BM, French RJ, Yoshikami D. Synergistic and antagonistic interactions between tetrodotoxin and mu-conotoxin in blocking voltage-gated sodium channels. Channels (Austin) 2009; 3:32-8. [PMID: 19221510 DOI: 10.4161/chan.3.1.7500] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Tetrodotoxin (TTX) is the quintessential ligand of voltage-gated sodium channels (NaVs). Like TTX, mu-conotoxin peptides are pore blockers, and both toxins have helped to define the properties of neurotoxin receptor Site 1 of NaVs. Here, we report unexpected results showing that the recently discovered mu-conotoxin KIIIA and TTX can simultaneously bind to Site 1 and act in concert. Results with saturating concentrations of peptide applied to voltage-clamped Xenopus oocytes expressing brain NaV1.2, and single-channel recordings from brain channels in lipid bilayers, show that KIIIA or its analog, KIIIA[K7A], block partially, with a residual current that can be completely blocked by TTX. In addition, the kinetics of block by TTX and peptide are each affected by the prior presence of the other toxin. For example, bound peptide slows subsequent binding of TTX (an antagonistic interaction) and slows TTX dissociation when both toxins are bound (a synergistic effect on block). The overall functional consequence resulting from the combined action of the toxins depends on the quantitative balance between these opposing actions. The results lead us to postulate that in the bi-liganded NaV complex, TTX is bound between the peptide and the selectivity filter. These observations refine our view of Site 1 and open new possibilities in NaV pharmacology.
Collapse
Affiliation(s)
- Min-Min Zhang
- Department of Biology, University of Utah, Salt Lake City, UT 84112, USA
| | | | | | | | | | | | | |
Collapse
|
4
|
Zhang MM, Green BR, Catlin P, Fiedler B, Azam L, Chadwick A, Terlau H, McArthur JR, French RJ, Gulyas J, Rivier JE, Smith BJ, Norton RS, Olivera BM, Yoshikami D, Bulaj G. Structure/Function Characterization of μ-Conotoxin KIIIA, an Analgesic, Nearly Irreversible Blocker of Mammalian Neuronal Sodium Channels. J Biol Chem 2007; 282:30699-706. [PMID: 17724025 DOI: 10.1074/jbc.m704616200] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Peptide neurotoxins from cone snails continue to supply compounds with therapeutic potential. Although several analgesic conotoxins have already reached human clinical trials, a continuing need exists for the discovery and development of novel non-opioid analgesics, such as subtype-selective sodium channel blockers. Micro-conotoxin KIIIA is representative of micro-conopeptides previously characterized as inhibitors of tetrodotoxin (TTX)-resistant sodium channels in amphibian dorsal root ganglion neurons. Here, we show that KIIIA has potent analgesic activity in the mouse pain model. Surprisingly, KIIIA was found to block most (>80%) of the TTX-sensitive, but only approximately 20% of the TTX-resistant, sodium current in mouse dorsal root ganglion neurons. KIIIA was tested on cloned mammalian channels expressed in Xenopus oocytes. Both Na(V)1.2 and Na(V)1.6 were strongly blocked; within experimental wash times of 40-60 min, block was reversed very little for Na(V)1.2 and only partially for Na(V)1.6. Other isoforms were blocked reversibly: Na(V)1.3 (IC50 8 microM), Na(V)1.5 (IC50 284 microM), and Na(V)1.4 (IC50 80 nM). "Alanine-walk" and related analogs were synthesized and tested against both Na(V)1.2 and Na(V)1.4; replacement of Trp-8 resulted in reversible block of Na(V)1.2, whereas replacement of Lys-7, Trp-8, or Asp-11 yielded a more profound effect on the block of Na(V)1.4 than of Na(V)1.2. Taken together, these data suggest that KIIIA is an effective tool to study structure and function of Na(V)1.2 and that further engineering of micro-conopeptides belonging to the KIIIA group may provide subtype-selective pharmacological compounds for mammalian neuronal sodium channels and potential therapeutics for the treatment of pain.
Collapse
Affiliation(s)
- Min-Min Zhang
- Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
5
|
French RJ, Worley JF, Wonderlin WF, Kularatna AS, Krueger BK. Ion permeation, divalent ion block, and chemical modification of single sodium channels. Description by single- and double-occupancy rate-theory models. J Gen Physiol 1994; 103:447-70. [PMID: 8037798 PMCID: PMC2216843 DOI: 10.1085/jgp.103.3.447] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Calcium ions, applied internally, externally, or symmetrically, have been used in conjunction with rate-theory modeling to explore the energy profile of the ion-conducting pore of sodium channels. The block, by extracellular and/or intracellular calcium, of sodium ion conduction through single, batrachotoxin-activated sodium channels from rat brain was studied in planar lipid bilayers. Extracellular calcium caused a reduction of inward current that was enhanced by hyperpolarization and a weaker block of outward current. Intracellular calcium reduced both outward and inward sodium current, with the block being weakly dependent on voltage and enhanced by depolarization. These results, together with the dependence of single-channel conductance on sodium concentration, and the effects of symmetrically applied calcium, were described using single- or double-occupancy, three-barrier, two-site (3B2S), or single-occupancy, 4B3S rate-theory models. There appear to be distinct outer and inner regions of the channel, easily accessed by external or internal calcium respectively, separated by a rate-limiting barrier to calcium permeation. Most of the data could be well fit by each of the models. Reducing the ion interaction energies sufficiently to allow a small but significant probability of two-ion occupancy in the 3B2S model yielded better overall fits than for either 3B2S or 4B3S models constrained to single occupancy. The outer ion-binding site of the model may represent a section of the pore in which sodium, calcium, and guanidinium toxins, such as saxitoxin or tetrodotoxin, compete. Under physiological conditions, with millimolar calcium externally, and high potassium internally, the model channels are occupied by calcium or potassium much of the time, causing a significant reduction in single-channel conductance from the value measured with sodium as the only cation species present. Sodium conductance and degree of block by external calcium are reduced by modification of single channels with the carboxyl reagent, trimethyloxonium (TMO) (Worley et al., 1986) Journal of General Physiology. 87:327-349). Elevations of only the outermost parts of the energy profiles for sodium and calcium were sufficient to account for the reductions in conductance and in efficacy of calcium block produced by TMO modification.
Collapse
Affiliation(s)
- R J French
- Department of Medical Physiology, University of Calgary, Alberta, Canada
| | | | | | | | | |
Collapse
|
6
|
Dudley SC, Baumgarten CM. Modification of cardiac sodium channels by carboxyl reagents. Trimethyloxonium and water-soluble carbodiimide. J Gen Physiol 1993; 101:651-71. [PMID: 8393064 PMCID: PMC2216784 DOI: 10.1085/jgp.101.5.651] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
In TTX-sensitive nerve and skeletal muscle Na+ channels, selective modification of external carboxyl groups with trimethyloxonium (TMO) or water-soluble carbodiimide (WSC) prevents voltage-dependent Ca2+ block, reduces unitary conductance, and decreases guanidinium toxin affinity. In the case of TMO, it has been suggested that all three effects result from modification of a single carboxyl group, which causes a positive shift in the channel's surface potential. We studied the effect of these reagents on Ca2+ block of adult rabbit ventricular Na+ channels in cell-attached patches. In unmodified channels, unitary conductance (gamma Na) was 18.6 +/- 0.9 pS with 280 mM Na+ and 2 mM Ca2+ in the pipette and was reduced to 5.2 +/- 0.8 pS by 10 mM Ca2+. In contrast to TTX-sensitive Na+ channels, Ca2+ block of cardiac Na+ channels was not prevented by TMO; after TMO pretreatment, gamma Na was 6.1 +/- 1.0 pS in 10 mM Ca2+. Nevertheless, TMO altered cardiac Na+ channel properties. In 2 mM Ca2+, TMO-treated patches exhibited up to three discrete gamma Na levels: 15.3 +/- 1.7, 11.3 +/- 1.5, and 9.8 +/- 1.8 pS. Patch-to-patch variation in which levels were present and the absence of transitions between levels suggests that at least two sites were modified by TMO. An abbreviation of mean open time (MOT) accompanied each decrease in gamma Na. The effects on channel gating of elevating external Ca2+ differed from those of TMO pretreatment. Increasing pipette Ca2+ from 2 to 10 mM prolonged the MOT at potentials positive to approximately -35 mV by decreasing the open to inactivated (O-->I) transition rate constant. On the other hand, even in 10 mM Ca2+ TMO accelerated the O-->I transition rate constant without a change in its voltage dependence. Ensemble averages after TMO showed a shortening of the time to peak current and an acceleration of the rate of current decay. Channel modification with WSC resulted in analogous effects to those of TMO in failing to show relief from block by 10 mM Ca2+. Further, WSC caused a decrease in gamma Na and an abbreviation of MOT at all potentials tested. We conclude that a change in surface potential caused by a single carboxyl modification is inadequate to explain the effects of TMO and WSC in heart. Failure of TMO and WSC to prevent Ca2+ block of the cardiac Na+ channel is a new distinction among isoforms in the Na+ channel multigene family.
Collapse
Affiliation(s)
- S C Dudley
- Department of Physiology, Medical College of Virginia, Richmond 23298-0551
| | | |
Collapse
|
7
|
Schild L, Moczydlowski E. Competitive binding interaction between Zn2+ and saxitoxin in cardiac Na+ channels. Evidence for a sulfhydryl group in the Zn2+/saxitoxin binding site. Biophys J 1991; 59:523-37. [PMID: 1646656 PMCID: PMC1281218 DOI: 10.1016/s0006-3495(91)82269-x] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Mammalian heart Na+ channels exhibit approximately 100-fold higher affinity for block by external Zn2+ than other Na+ channel subtypes. With batrachotoxin-modified Na+ channels from dog or calf heart, micromolar concentrations of external Zn2+ result in a flickering block to a substate level with a conductance of approximately 12% of the open channel at -50 mV. We examined the hypothesis that, in this blocking mode, Zn2+ binds to a subsite of the saxitoxin (STX) binding site of heart Na+ channels by single-channel analysis of the interaction between Zn2+ and STX and also by chemical modification experiments on single heart Na+ channels incorporated into planar lipid bilayers in the presence of batrachotoxin. We found that external Zn2+ relieved block by STX in a strictly competitive fashion. Kinetic analysis of this phenomenon was consistent with a scheme involving direct binding competition between Zn2+ and STX at a single site with intrinsic equilibrium dissociation constants of 30 nM for STX and 30 microM for Zn2+. Because high-affinity Zn2(+)-binding sites often include sulfhydryl groups as coordinating ligands of this metal ion, we tested the effect of a sulfhydryl-specific alkylating reagent, iodoacetamide (IAA), on Zn2+ and STX block. For six calf heart Na+ channels, we observed that exposure to 5 mM IAA completely abolished Zn2+ block and concomitantly modified STX binding with at least 20-fold reduction in affinity. These results lead us to propose a model in which Zn2+ binds to a subsite within or near the STX binding site of heart Na+ channels. This site is also presumed to contain one or more cysteine sulfhydryl groups.
Collapse
Affiliation(s)
- L Schild
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510
| | | |
Collapse
|
8
|
Ravindran A, Schild L, Moczydlowski E. Divalent cation selectivity for external block of voltage-dependent Na+ channels prolonged by batrachotoxin. Zn2+ induces discrete substates in cardiac Na+ channels. J Gen Physiol 1991; 97:89-115. [PMID: 1848885 PMCID: PMC2216464 DOI: 10.1085/jgp.97.1.89] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The mechanism of block of voltage-dependent Na+ channels by extracellular divalent cations was investigated in a quantitative comparison of two distinct Na+ channel subtypes incorporated into planar bilayers in the presence of batrachotoxin. External Ca2+ and other divalent cations induced a fast voltage-dependent block observed as a reduction in unitary current for tetrodotoxin-sensitive Na+ channels of rat skeletal muscle and tetrodotoxin-insensitive Na+ channels of canine heart ventricular muscle. Using a simple model of voltage-dependent binding to a single site, these two distinct Na+ channel subtypes exhibited virtually the same affinity and voltage dependence for fast block by Ca2+ and a number of other divalent cations. This group of divalent cations exhibited an affinity sequence of Co congruent to Ni greater than Mn greater than Ca greater than Mg greater than Sr greater than Ba, following an inverse correlation between binding affinity and ionic radius. The voltage dependence of fast Ca2+ block was essentially independent of CaCl2 concentration; however, at constant voltage the Ca2+ concentration dependence of fast block deviated from a Langmuir isotherm in the manner expected for an effect of negative surface charge. Titration curves for fast Ca2+ block were fit to a simplified model based on a single Ca2+ binding site and the Gouy-Chapman theory of surface charge. This model gave similar estimates of negative surface charge density in the vicinity of the Ca2+ blocking site for muscle and heart Na+ channels. In contrast to other divalent cations listed above, Cd2+ and Zn2+ are more potent blockers of heart Na+ channels than muscle Na+ channels. Cd2+ induced a fast, voltage-dependent block in both Na+ channel subtypes with a 46-fold higher affinity at 0 mV for heart (KB = 0.37 mM) vs. muscle (KB = 17 mM). Zn2+ induced a fast, voltage-dependent block of muscle Na+ channels with low affinity (KB = 7.5 mM at 0 mV). In contrast, micromolar Zn2+ induced brief closures of heart Na+ channels that were resolved as discrete substate events at the single-channel level with an apparent blocking affinity of KB = 0.067 mM at 0 mV, or 110-fold higher affinity for Zn2+ compared with the muscle channel. High-affinity block of the heart channel by Cd2+ and Zn2+ exhibited approximately the same voltage dependence (e-fold per 60 mV) as low affinity block of the muscle subtype (e-fold per 54 mV), suggesting that the block occurs at structurally analogous sites in the two Na+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)
Collapse
Affiliation(s)
- A Ravindran
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510
| | | | | |
Collapse
|
9
|
Lönnendonker U. Binding of tetrodotoxin and saxitoxin to Na+ channels at different holding potentials: fluctuation measurements in frog myelinated nerve. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 985:161-7. [PMID: 2553116 DOI: 10.1016/0005-2736(89)90361-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The number of available Na+ channels in nodes of frog nerve fibres was determined from nonstationary Na+ current fluctuations recorded during a train of depolarizing test pulses. Mean numbers in Ringers's solution were 90,000 at a hyperpolarizing holding potential VH = -40 mV, 50,000 at the resting potential (VH = 0 mV) and 30,000 at a depolarizing holding potential VH = 30 mV. Addition of the cationic channel blockers tetrodotoxin (TTX) or saxitoxin (STX) to Ringer reduced the channel number by a factor which was independent of the holding potential. The reduction factor was 4 for 9.3 nM TTX and 3 for 3.5 nM STX. Thus, in the state of repetitive stimulation, TTX or STX blockage of Na+ channels is hardly affected by the membrane potential. Taking into account use-dependent TTX and STX effects [1], it is concluded that binding of both toxins exhibits a weak voltage dependence with toxin affinities decreasing at more negative holding potentials. The results suggest that binding of TTX and STX occurs at an external superficial receptor near the Na+ channel and that the toxin affinity of the receptor may be modulated by fast Na+ activation and slow inactivation gating processes.
Collapse
Affiliation(s)
- U Lönnendonker
- I. Physiologisches Institut der Universität des Saarlandes, Homburg/Saar, F.R.G
| |
Collapse
|
10
|
|
11
|
Agnew WS, Tomiko SA, Rosenberg RL, Emerick MC, Cooper EC. The structure and function of the voltage-sensitive Na channel. Ann N Y Acad Sci 1986; 479:238-56. [PMID: 2433994 DOI: 10.1111/j.1749-6632.1986.tb15573.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
|