Synthetic Pinnatoxins A and G Reversibly Block Mouse Skeletal Neuromuscular Transmission In Vivo and In Vitro

Pinnatoxins (PnTXs) A-H constitute an emerging family belonging to the cyclic imine group of phycotoxins. Interest has been focused on these fast-acting and highly-potent toxins because they are widely found in contaminated shellfish. Despite their highly complex molecular structure, PnTXs have been chemically synthetized and demonstrated to act on various nicotinic acetylcholine receptor (nAChR) subtypes. In the present work, PnTX-A, PnTX-G and analogue, obtained by chemical synthesis with a high degree of purity (>98%), have been studied in vivo and in vitro on adult mouse and isolated nerve-muscle preparations expressing the mature muscle-type (α1)₂β1δε nAChR. The results show that PnTX-A and G acted on the neuromuscular system of anesthetized mice and blocked the compound muscle action potential (CMAP) in a dose- and time-dependent manner, using a minimally invasive electrophysiological method. The CMAP block produced by both toxins in vivo was reversible within 6–8 h. PnTX-A and G, applied to isolated extensor digitorum longus nerve-muscle preparations, blocked reversibly isometric twitches evoked by nerve stimulation. The action of PnTX-A was reversed by 3,4-diaminopyridine. Both toxins exerted no direct action on muscle fibers, as revealed by direct muscle stimulation. PnTX-A and G blocked synaptic transmission at mouse neuromuscular junctions and PnTX-A amino ketone analogue (containing an open form of the imine ring) had no effect on neuromuscular transmission. These results indicate the importance of the cyclic imine for interacting with the adult mammalian muscle-type nAChR. Modeling and docking studies revealed molecular determinants responsible for the interaction of PnTXs with the muscle-type nAChR.

3,16-Bisquaternary ammonium steroid derivatives as neuromuscular blocking agents: synthesis and biological evaluation

Neuromuscular blocking agents (NMBAs) are widely used in surgery to achieve skeleton muscles relaxation under light anesthesia status. In this work, we synthesized a series of 3,16-bisquaternary ammonium steroidal NMBAs. Among them, three compounds exhibited higher in vitro activities than the commenced drug rocuronium. In addition, structure-activity relationship was unveiled. We found that the intact acetylcholine-like moiety in D-ring was not necessary for maintaining activity but both the acetyl group and the quaternary nitrogen were very essential.

Synthesis of quaternary ammonium salts of 16E-[4-(2-alkylaminoethoxy)-3-methoxybenzylidene]androstene derivatives as skeletal muscle relaxants

Synthesis of eighteen new quaternary ammonium salts of 16E-arylidene androstene derivatives as skeletal muscle relaxants is reported in the present study. The effects of possibly extended interonium distances on muscle relaxant activity are discussed. All the quaternary ammonium steroids produced reduction in the twitch responses, when screened for in vitro neuromuscular blocking activity using isolated chick biventer cervicis muscle preparation. However, the variable interonium distance, which is believed to range from 11 to 17 Å in these quaternary compounds and is associated with the built in flexibility of these structures about the single bonds on the moieties linked to ring D of the steroid skeleton, resulted in varied degrees of muscle relaxant activity. Some of the compounds also inhibited acetylcholinesterase activity in low concentrations so that they would not be directly suitable for use as muscle relaxants.

Recent Advances in Neuromuscular Blocking Agents

Since the introduction of (+)-tubocurarine into anaesthetic and surgical practice (1942), a number of non-depolarizing neuromuscular blocking agents (NMBs) with improved pharmacological properties have been developed during the last sixty years. However, after withdrawal of rapacuronium from clinical use, there is still a need for an ultra-short acting non-depolarizing muscle relaxant with rapid onset as substitution for the polarizing suxamethonium, which has several undesirable side-effects. In this paper, structure-activity relationships within four different series of NMBs (tetrahydroisoquinolinium, bistropinyl diester, aminosteroid, and amino peptide analogues) published in this millennium have been reviewed. The NMB properties of the most promising drug candidates from each series were discussed and compared to those of the already existing muscle relaxants.

Neuromuscular blocking activity and therapeutic potential of mixed-tetrahydroisoquinolinium halofumarates and halosuccinates in rhesus monkeys

Structure-activity relationships in rhesus monkeys for a novel mixed-onium class of ultra-short-acting nondepolarizing tetrahydroisoquinolinium neuromuscular blockers (NMBs) are described. Bis-onium chlorofumarate 20a with (1R,2S)-benzyltetrahydroisoquinolinium groups was a potent lead compound (ED(95) = 0.079 mg/kg) with an ultra-short duration of NMB effect (7.1 min) and a selectivity index (SI: defined as a ratio of the cardiovascular threshold dose to the ED(95)) similar to that of mivacurium (3). The mean threshold dose for cardiovascular effects with 20a was ca. 20 times its ED(95) value (SI = 20). A novel mixed-onium analogue of 20a was prepared by replacing the benzyltetrahydroisoquinolinium group distal to the fumarate chlorine atom with a (1S,2R)-phenyltetrahydroisoquinolinium moiety. The resulting mixed-onium chlorofumarate 24a displayed good NMB potency (ED(95) = 0.063 mg/kg), ultra-short duration of action (5.6 min) and an improved selectivity index (SI = 57). Several other mixed-onium derivatives containing octanedioate (25a; ED(95) = 0.103 mg/kg), difluorosuccinate (27c; ED(95) = 0.056 mg/kg), and fluorofumarate (28a; ED(95) = 0.137 mg/kg) linkers were also potent, ultra-short-acting NMBs with good to excellent selectivity index values (SI = 37-96). Octanedioate 25a was longer acting at higher doses compared to difluorosuccinate 27c and chlorofumarate 24a. Durations of NMB effect following a 0.4 mg/kg bolus dose (100% block) of 25a, 27c, and 24a were 16.9, 13.0, and 10.0 min, respectively. Recovery time for mixed-onium chlorofumarate 24a following a 1 h continuous infusion at 10-20 microg/kg/min (95-100% block) was ca. 5 min which is similar to that observed following a 0.2 mg/kg bolus dose of this compound and indicates a lack of cummulative effects. Preliminary studies with chlorofumarate 24a in whole human blood revealed that mixed-onium thiazolidine 29 was the major metabolite and that plasma cholinesterases do not play the primary role in duration of NMB effect. The NMB properties of 24a in rhesus monkeys led to its clinical evaluation as a possible alternative to succinylcholine.

Synthesis and biological evaluation of 16 beta-pyrrolidinosteroidal derivatives

The synthesis of some steroidal bisquaternary ammonium substances (compounds 10 and 11), and their in vitro and in vivo neuromuscular blocking action are described in this report. The pyrrolidino functionality was incorporated at both the 3-beta and 16-beta positions of the steroid nucleus to study the importance of the interonium distance between the two quaternary ammonium heads. The 16-beta-pyrrolidino monoquaternary derivatives (compounds 14, 15, 16) were also prepared. The 17-beta-acetoxy bisquaternary derivative compound 11 was found to be more potent than d-tubocurarine (CAS 57-94-3) in in vivo studies. The 17-beta-hydroxy bisquaternary derivative, compound 10, and its 16-beta-pyrrolidino monoquaternary partner, compound 15, were found to be less active as compared to d-tubocurarine in in vitro studies. The monoquaternary compounds 14 and 16 were not tested due to their solubility problems. The intermediate substance, compound 12 was selected by the National Cancer Institute (NCI), Bethesda (USA) for investigation for antineoplastic activity but was found to be inactive.

Synthesis and neuromuscular blocking activity of 16beta-N-methylpiperazino steroidal derivatives

Steroidal quaternary ammonium compounds 12 and 13 with quaternised nitrogen at positions 3 and 16 of the steroidal nucleus in androstane series were synthesised and their neuromuscular blocking activities and ganglion blocking activities were studied using chick biventer and anaesthetised cat as the models. The bisquaternary compounds 12 and 13 have been found to be greater in potency than D-tubocurarine. Acetoxy derivative 13 has been found to be more potent than pipecuronium bromide taking D-tubocurarine as the standard compound indicating the need of acetoxy function at position 16.

Identification of four additional myoinhibitory peptides (MIPs) from the ventral nerve cord of Manduca sexta

Four new myoinhibitory peptides were isolated and identified from the ventral nerve cord of adult Manduca sexta. The new peptides are related to two previously identified myoinhibitory peptides also isolated from adult M. sexta, Mas-MIP I and Mas-MIP II. The sequences of the new peptides are APEKWAAFHGSWamide (Mas-MIP III), GWNDMSSAWamide (Mas-MIP IV), GWQDMSSAWamide (Mas-MIP V), and AWSALHGAWamide (Mas-MIP VI). Mas-MIPs III-VI were found to inhibit spontaneous peristalsis of the adult M. sexta anterior hindgut (ileum) in vitro.

Synthesis and neuromuscular blocking activity of 16beta-piperidinosteroidal derivatives

The synthesis and pharmacological profiles of some new steroidal mono- and bisquaternary ammonium derivatives have been described. The compounds featured have been conceptually derived structurally from two lead structures: pancuronium bromide 1 and chandonium iodide 2. In vitro and in vivo neuromuscular blocking studies have indicated the monoquaternary compound 15 to be less active than the bisquaternary compounds 10 and 11. The compound 11 has been found to be more active than d-tubocurarine.

Atropisomeric quinazolin-4-one derivatives are potent noncompetitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists

Piriqualone (1) was found to be an antagonist of AMPA receptors. Structure activity optimization was conducted on each of the three rings in 1 to afford a series of potent and selective antagonists. The sterically crowded environment surrounding the N-3 aryl group provided sufficient thermal stability for atropisomers to be isolated. Separation of these atropisomers resulted in the identification of (+)-38 (CP-465,022), a compound that binds to the AMPA receptor with high affinity (IC50 = 36 nM) and displays potent anticonvulsant activity.

Synthesis of ultra-short-acting neuromuscular blocker GW 0430: a remarkably stereo- and regioselective synthesis of mixed tetrahydroisoquinolinium chlorofumarates

[formula: see text] The stereo- and regioselective synthesis of ultra-short-acting nondepolarizing neuromuscular blocker GW 0430 (5a) is described. Key steps involved the enantioselective transfer hydrogenation of imine 8 employing Noyori's catalyst, the stereoselective crystallization and methanolysis of trans-bataines 11 and 12, and the stereo- and regioselective trans elimination of hydrogen chloride from 14. The latter transformation allowed complete control of the position of the chloro substituent and stereochemistry at the double bond of the linker in 15.

Study on steroidal oximinoethers: synthesis and stereostructure by NMR spectroscopy

The condensation of O-substituted hydroxylamines with conjugated 3-oxo-4-en steroids results in a mixture of syn-anti configurations. Syn-anti ratios are influenced by sterical hindrance between the oximino substituents (e.g. O-benzyl) and the steroidal skeleton. Stereostructures and isomeric ratios were proved by detailed 1H and 13C NMR studies and also by using 2D-COSY, 2D-HSC, DEPT, 2D-COLOC and DNOE measurements.

Potentiating effects of beta-eudesmol-related cyclohexylidene derivatives on succinylcholine-induced neuromuscular block in isolated phrenic nerve-diaphragm muscles of normal and alloxan-diabetic mice

beta-Eudesmol, a sesquiterpenoid alcohol contained in Atractylodes lancea, potentiates succinylcholine (SuCh)-induced neuromuscular blockade. The potentiating effect is greater in diabetic muscles than in normal ones. As a ligand for affinity chromatography to study the potentiating mechanism, we designed and synthesized newly beta-eudesmol-related cyclohexylidene derivatives (2-(3-hydroxy-3-methylbutyl)cyclohexylidene; KTE-13, 2-(3-hydroxy-3-methylbutyl)-4-cyclohexylidene carboxylic acid; KTE-32 and 4-tert-butoxycarbonyl-2-(3-hydroxy-3-methylbutyl) cyclohexylidene; KTE-33). We examined the potentiating effects of those compounds in phrenic nerve-diaphragm muscle preparations of normal and alloxan-diabetic mice. KTE-33 (100 microM) potentiated more greatly SuCh-induced neuromuscular blockade in diabetic muscles than in normal ones (the potentiating ratios in normal and diabetic muscles were 6.7 and 10.6, respectively), while KTE-13 (100 microM) and -32 (200 microM) potentiated weakly. These results suggest that the ester group in KTE-33 rather than a carboxyl group in KTE-32 is important in inducing the potentiation of SuCh-induced neuromuscular blockade in diabetic state.

The structure-activity relationship between phenylene-polymethylene bis-ammonium derivatives and their neuromuscular blocking action on mouse phrenic nerve-diaphragm muscle

The structure-activity relationship of phenylene-polymethylene bis-ammonium (PMBA) derivatives, C6H4[X(CH2)nR]2, on isolated mouse phrenic nerve-diaphragm muscle was investigated to obtain more potent and stable compounds for use as pharmacological tools to clarify the mechanism of succinylcholine (SuCh)-induced neuromuscular blockade. The neuromuscular blocking effect of all the PMBA derivatives was not reversed by neostigmine, a cholinesterase inhibitor. The potency of the neuromuscular blockade was in the order p- > o- > m- with respect to the side-chain substituents. A PMBA composed of X = CH2, n = 5 and R = N+Et3 was 5.9- and 23-fold more potent than SuCh and decamethonium, respectively. The derivatives of R = N+Et3 were observed to be more potent than those of R = N+Me3, N-Me-piperidinio and pyridinio derivatives. Replacement of X = CH2 with O, CHOH and CHOAc decreased the neuromuscular activity while replacement with S, SO and SO2 increased it. Introduction of NO2 into the phenylene ring increased the activity, while the introduction of an alcohol, aldehyde and ketone group decreased it. Removal of a carbonyl or ether group from SuCh decreased its activity, whereas the introduction of these into PMBA failed to increase it. We managed to synthesize unhydrolyzable neuromuscular blocking agents which are more potent than SuCh.

[Analysis of steroids. Part 44: Analytical investigation of the intermediates of the synthesis of pipecuronium bromide (Arduan)]

The following methods are described for the analytical investigation of the intermediates of the synthesis of pipecuronium bromide (Arduan) (for the numbering of the intermediates and their impurities see Figure 1.). 1. Gas chromatographic methods (capillary GC using fused silica capillaries Ultra-2 and Silar 10C WCOT) for the impurity profiling of intermediates I, II, IV and V including the identification and spectroscopic characterization of their impurities; 2. TLC methods for the similar characterisation of the further intermediates (III, VI, VII and VIII); 3. Gas chromatographic assay methods for IV and V using fused silica capillary technique and internal standards; 4. Potentiometric titration methods for the determination of VII and VIII using 0.1 M hydrochloric acid as the titrant.

[Synthesis of a new neuromuscular blocking agent, pipecuronium bromide (Arduan)]

A series of bisquaternary ammonio steroids having androstane skeleton have been prepared some of which possessed high neuromuscular blocking activity. One of the series 3 alpha, 17 beta-diacetoxy-2 beta, 16 beta-bis (4,4-dimethyl-1-piperazinyl)-5 alpha-androstane dibromide (19, pipecuronium bromide, ARDUAN) has proved to be a clinically useful agent of long duration of action without side effects. The preparation of pipecuronium bromide and its metabolites and the impurities are also described. The structure of 19 and related compounds was elucidated by spectrometric methods IR, NMR and MS.

Synthesis, stereochemical analysis, and neuromuscular blocking activity of oximino ether derivatives of progesterone

This study consists of the synthesis, separation, and stereochemical analysis of oximino ethers, followed by a preliminary pharmacological evaluation for neuromuscular blockade. Synthesis of the compounds began with the double oximation of progesterone, which yielded EE and ZE dioximes as major products. Both stereoisomers were separated and purified by chromatography followed by crystallization. The diether of each dioxime was prepared by O-alkylation with 2-dimethylaminoethyl chloride hydrochloride, using a mixture of potassium tert-butoxide and sodium hydride as base. The diethers were separated from the monoethers by vacuum chromatography. Configurational assignments of all compounds were based on 1HNMR and 13CNMR spectroscopy. Quaternization with methyl bromide yielded the salts which were purified via fractional crystallization. A preliminary pharmacological evaluation was conducted by using mice on a treadmill apparatus. Structure-activity relationships are discussed on the basis of similarities to succinylcholine.

Synthesis and pharmacological evaluation of imidazopyridinium derivatives as neuromuscular blocking agents

A series of new imidazo[1,2-a]pyridinium derivatives have been prepared and studied as neuromuscular blocking agents in rats. These new substances are structurally related to fazadinium whose heterocyclic moieties were retained. All the new synthetized compounds are endowed with competitive neuromuscular blocking activity both in vitro and in vivo. Some were found to be equieffective with fazadinium with similar cardiovascular effects while some others possess more favorable therapeutic indexes.

Histamine release by neuromuscular blocking agents in man

Several experimental and clinical studies have suggested that histamine is released following the administration of neuromuscular blocking agents, and that the histamine release is an important aspect in the hemodynamic response to the drug. We have measured plasma histamine following the administration of a series of neuromuscular blocking agents in man. Our data suggests that members of this class of drugs can cause a dose dependent release histamine release in man and that this release is hemodynamically significant. We have also evaluated the roles of rate of administration, of pretreatment with H1 and H2 antagonists and alterations in drug design as clinical strategies in attenuating the adverse reactions. The data obtained in humans can be shown to validate the cat model as a means of screening novel neuromuscular blocking agents.

Synthesis, stereochemical analysis, and neuromuscular blocking activity of selected E,E- and Z,Z-isomeric O-ethers of 4-androstene-3,17-dione dioximes

A number of selected geometric oxime ethers were synthesized as potential neuromuscular blocking agents. The study consisted of the synthesis, separation, and stereochemical analysis of selected compounds followed by a preliminary pharmacological evaluation for neuromuscular blockade. Synthesis of the compounds began with the double oximination of 4-androstene-3,17-dione followed by TLC, column chromatography, and fractional crystallization as the purification methods. These procedures yielded two of the possible four isomers. Configurational assignments on the isolated pair were based on experiments using IR, UV, and NMR spectroscopy. Isomerically pure diethers were prepared by two methods: (a) O-alkylation of the stereochemically pure dioximes with the appropriate aminoalkyl halide, and (b) O-alkylation of the dioxime mixture followed by quaternization and subsequent isolation of configurationally pure salts via fractional crystallization. A preliminary pharmacological evaluation was conducted by using mice on a treadmill apparatus. Some structure--activity relationships are discussed.

Structure-neuromuscular blocking activity relationships of ketophosphonium salts

Three ketophosphonium salts containing a morpholino group were prepared and evaluated for their neuromuscular blocking effect. Solution and crystal conformations were studied. An attempt was made to explain, in structural terms, different activity levels in connection with the interatomic distances.

Semisynthetic derivatives of pyrrolizidine alkaloids of pharmacodynamic importance: a review

Pyrrolizidine alkaloids occur in more than 40 genera. Among these are two important genera, Senecio and Crotalaria, which have been responsible for heavy losses of livestock and poisoning in man due to their hepatotoxicity. Pyrrolizidine alkaloids are also reported to possess a number of other biological activities. Attempts have been made to convert the pyrrolizidine alkaloids to new structures by synthetic modifications. One hundred and twenty semisynthetic compounds were developed and investigated pharmacologically. The range of activity exhibited was hypotensive, local anesthetic, ganglion blocking, neuromuscular blocking and antispasmodic. The five most promising compounds of these series were subjected to detailed pharmacological investigations.

Monoquaternary neuromuscular blocking agents based on 1-tetralone and 1-indanone

The preparation of three isomeric 1-tetralone hydrozones 4 and three isomeric 1-indanone hydrozones 5 possessing a single quaternary ammonium center is described. Several of the compounds possessed significant neuromuscular blocking activity, and two approached suxamethonium in potency. 1H NMR evidence obtained from a study of the N,N-dimethylhydrozones indicated that the hydrazones adopted an E configuration in solution.