Non-depolarising neuromuscular blockade by 3α,17α-bis(quaternary ammonium) 5α-androstanes

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.

Prelude to pancuronium and vecuronium

The discovery of the neuromuscular blocking activity of malouetine isolated from Malouetia bequaertiana Woodson by Quevauviller and Lainé in 1960 stimulated interest in aminosteroids as potential neuromuscular blockers. Alauddin (a pharmacist) and Martin-Smith (a medicinal chemist) began research in this area, which was then taken up by pharmaceutical companies. Pure pancuronium was synthesised in 1964 by Savage and his co-workers, directed by Hewett. Pharmacologists headed by Buckett discovered that pancuronium was far more potent than d-tubocurarine and had minimal side-effects. Buckett quickly recognised the value of pancuronium, and his persistence resulted in successful clinical trials, followed by the commercial launch of pancuronium in 1968. Vecuronium was synthesised, tested and the studies published by Buckett, Hewett and Savage in 1973, but this was before anaesthetists called for a 'clean muscle relaxant' and, furthermore, it was unstable in aqueous solution. Hence, it was only promoted for clinical trials six years later.

The neuromuscular and autonomic blocking activities of pancuronium, Org NC 45, and other pancuronium analogues, in the cat

Twenty-six mono- or bis-quaternary salts of 3,17-dioxy-2 beta, 16 beta-dipiperidino-5 alpha-androstanes (including pancuronium) and one 17-desoxy congener were tested for neuromuscular blocking and autonomic blocking activities in the chloralose-anaesthetized cat. The 17 beta-acetoxy series, all the members of which contain an acetylcholine-like fragment in the steroidal D-ring, was most selective for effecting neuromuscular blockade. The salient member of this series is 3 alpha, 17 beta-diacetoxy-2 beta, 16 beta-dipiperidino-5 alpha-androstane 16 beta-N-monomethobromide (Org NC 45) which is highly selective in blocking neuromuscular transmission in that a dose approximately sixty times greater than the neuromuscular blocking dose was required to block responses to vagal stimulation. In contrast, in doses sufficient to produce neuromuscular block, pancuronium simultaneously blocked responses to vagal stimulation. Moreover, pancuronium and Org NC 45 exhibited the same order of neuromuscular blocking activity and therefore the latter potentially represents a useful addition to the armamentarium of neuromuscular blocking agents currently in clinical use.

Steroidal monoquaternary ammonium salts with non-depolarizing neuromuscular blocking activity

A series of ten 2β- or 3α-steroidal monoquaternary ammonium salts, having androstane or pregnane skeletons and related in structure to acetylcholine by possession of an oxygen function on the carbon atom next but one to the quaternary nitrogen atom, were investigated for neuromuscular blocking activity in vivo in the cat, hen and mouse and in vitro on the frog rectus muscle and on the rat phrenic nerve diaphragm preparation. All compounds displayed typical non-depolarizing activity, the duration of block being significantly less than that for (+)-tubocurarine in the cat and the hen. The potency of the salts was low with the most active compound, 3α-acetoxy-2β-piperidino-5α-androstan-17-one methobromide, being 1/16th as active on a molar basis in the cat as (+)-tubocurarine.