WO2003070243A1

WO2003070243A1 - Di-ester derivatives as short acting neuromuscular blockers

Info

Publication number: WO2003070243A1
Application number: PCT/GB2003/000713
Authority: WO
Inventors: Gary Tilbrook
Original assignee: Therasci Limited
Priority date: 2002-02-21
Filing date: 2003-02-19
Publication date: 2003-08-28
Also published as: GB2385590A; GB0303850D0; GB0204087D0; AU2003207328A1

Abstract

The invention relates to substituted di-ester compounds joined by an alkylene linker group, in which each ester group independently is substituted by a nitrogen containing group in which the nitrogen is quaternised or is part of a guanidine group and derivatives, to pharmaceutical compositions, and to their use as medicaments as neuromuscular blocking agents. Preferred pharmaceutical compositions are those which are suitable for parenteral administration by intravenous or intramuscular or subcutaneous injection.

Description

Di-ester derivatives as short acting neuromuscular blockers.

The present invention relates to substituted di-ester compounds and derivatives, to pharmaceutical compositions comprising them and to methods and their use as medicaments as neuromuscular blocking agents.

In anaesthesia, neuromuscular blocking agents are utilised to relax skeletal muscle during surgery and to facilitate intubation of the trachea. Succinylcholine (suxamethonium) because of its rapid onset and fast recovery profile, is the historical standard among neuromuscular blockers and is the only ultra short acting neuromuscular blocker in clinical use. Succinylcholine acts as an agonist at the muscle nicotinic acetylcholine receptor causing membrane depolarisation and can produce a number of mechanism-related side-effects including fasciculations, myalgia, potassium release, cardiovascular effects (through ganglionic receptors), immunological reactions and malignant hyperthermia. Despite its undesirable side effect profile, no other ultrashort acting agent is available and therefore it is currently the preferred agent for emergency use.

Non-depolarising neuromuscular blockers are nicotinic acetylcholine receptor competitive antagonists and are devoid of the side-effects typically associated with depolarising relaxants. Non-depolarising agents are generally believed to be safer and more clinically desirable than depolarising agents and, anaesthesiologists have long recognised the need for a non-depolarising equivalent of succinylcholine [see Kopman, A., Journal of Clinical Anaesthesiology 5: 39S-45S (1993); Belmont, M.R., Current Opinion in Anaesthesiology, 8: 362-366 (1995)]. However, non-depolarising agents can elicit side-effects not related to their mechanism or duration of action. For example gallamine and pancuronium (long acting agents) can give rise to tachycardia. Shorter acting agents such as atracurium and mivacurium can also exhibit histamine release that may be associated with fatal anaphylactic reactions. It is therefore clearly evident that there exists an unsatisfied clinical need for new ultra short acting neuromuscular blocking agents possessing an improved safety profile.

Various compounds having muscle relaxant properties are detailed in US patent numbers: 4,190,674; 4,508,715; 4,761,418; 4,701,460; 4,179,507; 4,923,898; 5,015, 741 and 5,260,337. It has now been discovered that certain novel di-ester compounds are potent non- depolarising neuromuscular agents of short duration of action. These compounds offer significant advantages over currently used clinical agents by virtue of their rapid onset, and short duration of action. According to the present invention there are provided compounds comprising two ester groups joined by an alkylene linker group, in which each ester group independently is substituted by a nitrogen containing group in which the nitrogen is quatemised or is part of a guanidine group except for the following compounds: 4-{[(l-methylpyrrolidin- 2-yl)carbonyl]oxy}butyl l-methylpyrrolidine-2-carboxylate (and corresponding dimethylbenzene sulphonate and dimethiodide salt forms), 4-{[(l-methylpyrrolidin-2- yl)carbonyl]oxy} butyl l-ethylpyrrolidine-2-carboxylate (and corresponding diethiodide and dimethiodide salt forms), 4-{[(l-methylpyrrolidin-2-yl)carbonyl]oxy}butyl l-[(4- methylpiperazin-l-yl)methyl]pyrrolidine-2-carboxylate (and corresponding dimethiodide salt), 4-{[(l-ethylpyrrolidin-2-yl)carbonyl]oxy}butyl l-methylpyrrolidine-2-carboxylate (and corresponding dimethiodide salt), 4-{[(l-butylpyrrolidin-2-yl)carbonyl]oxy}butyl l-methylpyrrolidine-2-carboxylate (and corresponding dimethiodide salt).

The O atom in each of the ester groups may be attached to the alkylene linker group, or the C atom of the C=O group in each of the ester groups may be attached to the alkylene linker group. Thus the compounds may have: a) both ester groups linked to the alkylene linker group by their O atoms; b) both ester groups linked to the alkylene linker group by the C atom of their CO group; or c) one ester group linked to the alkylene linker group by its O atom and the other ester group linked to the alkylene linker group by the C atom of its C=O group. Preferred compounds are those in a) and b) above.

The alkylene linker group is preferably of formula -(CH )_n- in which n is an integer from 1 to 10, preferably n is 1, 2, 3, 4 or 5.

Preferred nitrogen containing groups are selected from:

(a) (b) (c) (d)

(e) (f) (9) (h)

in which R₃ and R each independently is selected from hydrogen, -(C=NH)NH₂₎ Ci-C₄ -alkyl, C_2-6

-alkenyl and optionally substituted C ι- -alkylphenyl; m is an integer selected from 0, 1 or 2; and

* signifies the point of attachment to the ester group.

Where R₃ and R₄ each independently is C_2-6 -alkenyl, each is preferably allyl. Where R₃ and P^ each independently is optionally substituted C _1-4-alkylphenyl, each is preferably benzyl or benzyl optionally substituted by one or more groups selected from

NO₂, halo, C_1-4-alkoxy, O(C=O)Cι_-4-alkyl, trihalomethyl and cyano.

A preferred sub-group of compounds of the present invention are di-esters of

Formula (I)

⁽0 wherein: n = integer from 1 to 10, preferably 1, 2, 3, 4 or 5; and

Rj_. and R each independently is selected from the preferred nitrogen containing groups defined above. In compounds of Formula (I) the nitrogen containing group is preferably one of those represented by (a), (b), (c), (d), (e), (g) or (h) above, more preferably (a), (b), (c) or

(h).

In one sub-set of compounds of Formula (I) n is preferably 1, 2, 3 or 5. In a further sub-set of compounds of Formula (T) n is preferably 4 provided both R_\ and R₂ are not N-alkyl pyrrolidine groups.

A further preferred sub-group of compounds of the present invention are di-esters of Formula (II)

(ii) wherein: n = integer from 1, 2, 3, 4 or 5; and

Rji and R₂ each independently is selected from the preferred nitrogen containing groups defined above.

In compounds of the present invention where in the nitrogen containing groups represented by (a) to (h) m = 0 the group is attached directly to a carbonyl carbon atom or an O atom. Where m=l there is one carbon atom linking the nitrogen containing groups represented by (a) to (h) to a carbonyl carbon atom or an O atom, where m=2 there are two carbon atoms linking the nitrogen, etc.

It will be apparent to those skilled in the art that the derivatives contain quatemised ammonium nitrogen atoms or is part of a guanidine group. These cationic compounds will exist together with counter-ions (anions).

For therapeutic purposes, it is preferable to use pharmaceutically acceptable anions such as iodide, mesylate, tosylate, bromide, chloride, hydrogen sulphate, sulphate/2, phosphate/3, hydrogen phosphate/2, acetate, besylate, succinate/2, maleate, napthalenesulphonate, propionate, ethanesulfonate, fumarate, citrate, nitrate, succinate, ascorbate, glutamate and benzoate.

It will also be apparent to those skilled in the art that a variety of optical isomers, enantiomeric pairs, and diastereomeric pairs exist for many of the compounds within the scope of the present invention. All such compounds are included in the present invention, as are all mixtures of optical isomers, enantiomeric pairs and diastereoisomer pairs, for each structural variation, including all pure compounds and racemic mixtures. Both cis and trans geometrical isomers and mixtures are also included in the present invention.

The compounds of the present invention in which both ester groups are linked to the alkylene linker group by their O atoms generally may be prepared by reacting a substituted methanol, in which the substituent is, for example, a nitrogen containing group represented by (a), (b), (c), (d), (e), (f), (g) or (h) above, with a substituted and/or protected guanidine which in turn is reacted with a dialkanoyldihalide. The first reaction may be carried out in an anhydrous liquid medium in the presence of an organic base such as triethylamine at ambient temperatures. Suitable liquid media include haloalkanes such as dichloromethane. The second reaction may be carried out in an anliydrous liquid medium in the presence of an acid such as trifluoroacetic acid again at ambient temperatures. Removal of the liquid media followed by usual purification techniques such as column chromatography (using for example SiO₂ and ethyl acetate/hexane as eluent) or diffusion crystallisation with diethyl ether give the desired products. Alternatively the substituted methanol, in which the substituent is, for example, a nitrogen containing group represented by (a), (b), (c), (d), (e), (f), (g) or (h) above, may be reacted directly with a dialkanoyldihalide in a liquid medium such as a haloalkane, for example dichloromethane.

The preparation of compounds of the present invention may be further illustrated by the following:

Bis-Boc-triflyl- guanidine (Boc = t-butoxycarbonyl) and 3-piperidinyl methanol react to give a protected guanylated piperidinyl alcohol (Scheme 1).

Scheme 1

further reaction with either pimeoyl (n=5) or glutaryl (n=3) chlorides (Scheme 2):

c

Scheme 2

give the expected product, which can be deprotected using trifluroacetic acid in dichloromethane (Scheme 3) to give compounds where n = 5 and where n = 3 respectively (Scheme 3):

Scheme 3

Scheme 4

Reaction of N-methyl-piperidinyl-3 -methanol with glutaryl chloride in dichloromethane gives an intermediate compound where n =3. Reaction of the intermediate compound with iodomethane in isopropyl alcohol gives the di-methylated derivative where n = 3

(Scheme 4). The compound where n = 5 can be prepared analogously using pimeoyl chloride instead of glutaryl chloride.

The compounds of the present invention in which both ester groups are linked to the alkylene linker group by the C atom of their C=O group generally may be prepared by reacting a compound of formula HO-(CH₂)_n-OH, in which n is as defined earlier, with an active carbonyl derivative, such as an acid, acid chloride, acid anhydride or ester of a preferred nitrogen containing groups of formula (a) to (h).

The compounds of the present invention in which one ester group linked to the alkylene linker group by its O atom and the other ester group linked to the alkylene linker group by the C atom of its C=O group generally may be prepared by protecting the

OH group of a compound of formula HO-(CH )_n-CO₂H, in which n is as defined earlier, with a hydroxyl derivative of a preferred nitrogen containing groups of formula (a) to

(h), followed by de-protecting the OH group and reacting it with an active carbonyl derivative, such as an acid, acid chloride, acid anhydride or ester of a preferred nitrogen containing groups of formula (a) to (h).

According to a further feature of the present invention there is provided a pharmaceutical composition comprising a compound of Formula (I) or (II) and one or more pharmaceutically acceptable diluents or carriers. Preferred pharmaceutical compositions are those which are suitable for parenteral administration. Compositions for parenteral use may be presented in the form of aqueous solutions, dispersions or emulsions. When a composition is to be administered intravenously or intramuscularly, it is preferred that the composition is in the form of a solution. Diluents suitable for use in the present invention include water, saline, alcohols e.g. ethanol and benzyl alcohol; esters e.g. benzyl benzoate, ethyl oleate, isopropyl myristate, isopropyl palmitate; aliphatic amides, e.g. N,N-dimethylacetamide, N- hydroxy-2-ethyl-lactamide; glycols and polyalcohols, e.g. propyleneglycol, glycerin; esters of polyalcohols, e.g. diacetine, triacetine; polyglycols and polyethers, e.g. polyethyleneglycol 400, propyleneglycol methylethers; dioxolanes, e.g. isopropylidenglycerin; dimethylisosorbide; pyrrolidone derivatives, e.g. 2-pyrrolidone, N-methyl-2-pyrrolidone, polyvinylpyrrolidone; polyoxyethylenated fatty alcohols, e.g., Brij®; esters of polyoxyethylenated fatty acids, e.g., Cremophor®, Myrj®; polysorbates, e.g., Tweens®; polyoxyethylene derivatives of polypropyleneglycols, e.g., Pluronics® and mixtures thereof.

The pharmaceutical compositions of the present invention may also contain pH adjusting agents, dispersing or wetting agents (such as lecithin or condensation products of an alkylene oxide with fatty acids), suspending agents (such as sodium carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, sodium alginate, polyvinyl-pyrrolidone, gum tragacanth and gum acacia), stabilizing agents, solubilizing agents, isotonic adjusting agents, solvents, pharmaceutically acceptable excipients such as preservatives parabens and methyl, ethyl or propyl p- hydroxybenzoate, benzalkonium chloride and benzylalcohol, antioxidants, chelating agents, e.g. EDTA, citric acid and phosphoric acid.

The pharmaceutical compositions of the present inventions are preferably within a pH range suitable for parenteral administration.

Compounds of Formula (I) and (II) exhibit neuromuscular blocking activity and according to a further feature of the present invention there is provided a method of inducing neuromuscular blockade in a mammal comprising administering to said mammal an effective neuromuscular paralysing amount of a compound of Formula (I) or

(II), or a pharmaceutical composition comprising a compound of Formula (I) or (LI) and one or more pharmaceutically acceptable diluents or carriers. The compounds and compositions of the present invention may be administered parenterally, e.g. by intravenous or intramuscular or subcutaneous injection, preferably by intravenous or intramuscular injection of a solution.

According to a further feature of the present invention there is provided a compound of Formula (I) or (LI), or a pharmaceutical composition comprising a compound of Formula (I) or (II) for use in therapy.

According to a further feature of the present invention there is provided a compound of Formula (I) or (II), or a pharmaceutical composition comprising a compound of Formula (I) or (II) for use as a medicament for inducing neuromuscular blockade in a mammal. According to a further feature of the present invention there is provided a use of a compound of Formula (I) or (II), or a pharmaceutical composition comprising a compound of Formula (I) or (II) for the manufacture of a medicament for inducing neuromuscular blockade in a mammal.

The compounds of Formula (I) and (II) are used as neuromuscular blocking agents during surgery, for intubation of the trachea, during electro-convulsive shock therapy and intensive care.

The following test methods, data and Examples illustrate the present invention: In Vitro Radioligand Receptor Binding Assay

The results in the above table were obtained using a well established in vitro radioligand receptor binding assay using [¹²⁵I]α-bungarotoxin and the BC₃H1 cell-line (membranes) that expresses the embryonic form of the human muscle-type nicotinic acetylcholine receptor. The method followed was as per Clementi and Sher (1985) European Journal of Cell Biology 37:220 with no modifications. Clinically useful neuromuscular blockers exert their action through binding to the muscle-type nicotinic acetylcholine receptor. Pancuronium bromide and tubocurarine are well known examples of neuromuscular blocking agents. The preparation of Examples 1 - 4 is described below.

Example 1 Pentanedioic acid bis-(l-carbamimidoyl-piperidin-3-ylmethyl) ester - bis- trifluroacetate derivative

a) [tert-Butoxycarbonylimino-(2-b.ydroxymethyl-piperidin-l-yl)-methyl]- carbamic acid tørt-butyl ester (intermediate 1) A 25 ml round bottom flask was charged with a stirrer bar, N,N'-his(tert- butoxycarbonyl)-N"-triflylguanidine (975 mg, 2.49 mmol), then anhydrous dichloromethane (DCM) (8 ml). A 10 ml round bottom flask was charged with piperidin-3-yl-methanol (315 mg, 1.1 equiv.), triethylamine (0.5 ml, 1.1 equiv.) and anhydrous DCM (5 ml). Once fully dissolved the second solution was added to the former, via syringe. After 18 hr of stirring the solution was decanted into a separating funnel containing KHSO₄ (2M, 10 ml). The mixture was separated, and the aqueous solution was further extracted with DCM (2 x 10 ml). The combined organics were washed with saturated NaHCO₃ (10 ml). The aqueous layer was further extracted with DCM (2 x 10 ml). The combined extracts were washed with saturated brine (10 ml), then the solvent was removed in vacuo to give a colourless foam. The compound was further purified by column chromatography (SiO₂) eluting first using hexanes / ethyl acetate

(3:7), then using ethyl acetate to give the above named product 518 mg, 60 %.

b) Heptanedioic acid bis-[l-(før^butoxycarbonylamino-te - butoxycarbonylimino-methyl)-piperidin-3-ylmethyl] ester (intermediate 2)

A 10 ml round bottom flask was charged with pimeoyl chloride (65 mg, 0.329 mmol) and anhydrous DCM (3ml). Separately a round bottom flask was charged with the [tert- butoxycarbonylimino-(2-hydroxymethyl-piperidin-l-yl)-methyl]-carbamic acid tert-butyl ester (259 mg, 2.2 equiv.), triethylamine (2.2 equiv., 74 mg) and DCM (3 ml). The latter solution was added to the former and the solution was stirred form 22 hrs. The reaction mixture was poured into saturated sodium carbonate (20 ml) and the product was extracted using ethyl acetate (3 x 20ml). The extracts were combined dried over sodium sulphate and the solvent was removed in vacuo. The product was further purified by column chromatography (SiO₂), eluting with ethyl acetate / hexanes (3:7) to give the above named product 14 mg, 5%.

c) Pentanedioic acid bis-[l-(tert-butoxycarbonylamino-fert- butoxycarbonylimino-methyl)-piperidin~3~ylmethyl] ester (intermediate 3)

This was made by an analogous method to the heptanoic acid derivative (intermediate 2) and 33 mg, 12.4% of the above named product was obtained.

d} Pentanedioic acid bis-(l-carbamimidoyl-piperidin-3-ylmethyl) ester - bis- trifluroacetate derivative

Pentanedioic acid bis-[l-(tert-butoxycarbonylamino-tert-butoxycarbonylimino-methyl)- piρeridin-3-ylmethyl] ester (23 mg, 27 μmol) was dissolved in DCM (3 ml) and trifluroacetic acid (1 ml) was added dropwise. The solution was stirred overnight. The solvents were removed in vacuo, and the resulting orange oil was taken up in the minimum quantity of acetonitrile (~ 0.2 ml). The compound was obtained as a colourless crystalline solid by diffusion crystallisation with diethyl ether (21 mg, quant.). 1H NMR: (CD₃CN): 4.020 (dd, J=l l.l, 5.2, 2H), 3.949 (dd, 1=11.2, 1.6, 2H), 3.691 (br d, J=14.8 2H), 3.626 (br d, 12.8, 2H) 3.067 (td, J=11.0 2.6, 2H), 2.926 (dd, J=10.2, 3.2,

2H), 2.409 (t, J=7.4, 4H), 2.198, 1.970 (solvent and water peaks overlying compound peaks), 1.611-1.557 (br m, 6H) 1.412-1.352 (br m, 6H).

Example 2

Heptanedioic acid bis-(l-carbamimidoyl-piperidin-3-ylmethyl) ester - bis- trifluroacetate derivative

Made by analogous method to pentanedioic acid bis-(l-carbamimidoyl-piperidin-3- ylmethyl) ester-bis-trifluroacetate derivative and 9 mg, 81% of product was obtained.

1H NMR: (CD₃CN): 3.789 (dd, J=11.4, 5.4, 2H), 3.700 (dd, J=10.4, 7.6, 2H), 3.457-

3.370 (br m, 4H), 2.833 (br t, 12.4, 2H), 2.698 (dd, J=10.2, 3.4, 2H), 2.117 (t, J=7.4, 4H),

1.956, 1.732 (solvent and water peaks overlying compound peaks), 1.390 (qu, J=7.7,

6H), 1.351 (br m, overlapping, 2H) 1.158-1.098 (br m, 5H).

Example 3

Pentanedioic acid bis-(l,l-dimethyl-piperidinium-3-ylmethyl) ester diiodide a) Pentanedioic acid bis-(l-methyl-piperidin-3-ylmethyl) ester (intermediate 4) Glutaryl chloride (169 mg, 1 mmol) was taken up in DCM (2.5 ml). (1 -Methyl-pip eridin- 3-yl)-methanol (388 mg, 3 mmol) was taken up in DCM (2.5 ml) and the latter solution was added dropwise to the former. The reaction was mildly exothermic. The reaction was stirred for 3 hrs., then added to saturated Na₂CO₃ (10 ml). The solution was extracted with ethyl acetate (4 x 15 ml), the combined extracts were dried over Na₂SO . The solvent was removed in vacuo. The resulting product was further purified by column chromatography (neutral alumina) eluting with ethyl acetate to give the above named product as yellow oil (203 mg, 57%).

b) Heptanedioic acid bis-(l-methyl-piperidin-3-ylmethyl) ester (intermediate 5)

This compound was made by an analogous method to pentanedioic acid bis-(l-methyl- piperidin-3-ylmethyl) ester, except that the chromatography was performed using ethanol /ethyl acetate / ammonia (20:80:1) on silica to give 230 mg, 60% of the above named product. c) Pentanedioic acid bis-(l,l-dimethyl-piperidinium-3-ylmethyl) ester diiodide

Pentanedioic acid bis-(l-methyl-piperidin-3-ylmethyl) ester (200 mg, 0.564 mmol) was taken up in 2-ρropanol (5 ml) and iodomethane (5 ml) was added. The solution was stirred at room temperature for 6 days, and the solvent was removed in vacuo, giving a brown sludgy solid. This was triturated in acetone to give the product as a yellow microcrystalline solid (165 mg)

1H NMR: (CD₃CN / D₂O {few drops}): 3.797 (dd, J=11.2, 5.0, 2H), 3.701 (dd, J=11.2,

6.4, 2H), 3.238 (br t, J=12, 4H), 2.983 (td, J=13.6, 4.4, 2H), 2.915, 2.130 (t, 4.6Hz, 4H) overlapping 2.130 (m, 2H), 1.744 (qu, J=2.5, 4H) 1.6-1.73 (possibly overlapping, m, 4H), 1.358 (qu., J=7.6, 4H), 1.02-1.12 (br m, 4H)

¹³C NMR (CD₃CN / D₂O {few drops}): 173.31 (C=O), 65.37 (CH2), 64.67 (CH2) 62.99

(CH2), 57.33 (CH3), 48.26 (CH3), 34.02 (CH2), 31.51 (CH), 24.23 (CH2), 19.93 (CH2).

Example 4 Heptanedioic acid bis-(l,l-dimethyl-piperidinium-3-ylmethyl) ester diiodide

This compound was made by an analogous method to the pentanedioic acid analogue, (Example 3) to give 352 mg 52.8% of the above named product.

1H NMR: (CD₃CN / D₂O {few drops}): 3.935 (dd, J=11.2, 4.8, 2H), 3.833 (dd, J=11.2, 6.8, 2H), 3.375-3.284 (br m, 4H), 3.120 (br td, 2H) 3.034 (s, 4H), 2.986-2.890 (br overlapping signals) 2.306 (t, 7.4 Hz, 4H) overlapping 2.254 (br m 2H), 1.861 (qu, 1=2.5, 4H) 1.72-1.810 (m, 9H), 1.190 (dd, J=8.0, 5.0, 2H)

¹³C NMR (CD₃CN / D₂O {few drops}): 173.76 (CO), 65.52 (CH2), 64.69 (CH2) 63.02 (CH2), 57.36 (CH3), 48.30 (CH3), 33.34 (CH2), 31.54 (CH), 24.24 (CH2), 20.39 (CH2), 19.97 (CH2).

Claims

1. A compound comprising two ester groups joined by an alkylene linker group, in which each ester group independently is substituted by a nitrogen containing group in which the nitrogen is quatemised or is part of a guanidine group except for the following compounds : 4- { [(1 -methylpyrrolidin-2-yl)carbonyl] oxy} butyl 1 -methylpyrrolidine-2- carboxylate (and corresponding dimethylbenzene sulphonate and dimethiodide salt forms), 4-{[(l-methylpyrrolidin-2-yl)carbonyl]oxy} butyl l-ethylpyrrolidine-2- carboxylate (and corresponding diethiodide and dimethiodide salt forms), 4-{[(l- methylpyrrolidin-2-yl)carbonyl]oxy} butyl l-[(4-methylpiperazin-l-l)methyl]ρyrrolidine- 2-carboxylate (and corresponding dimethiodide salt), 4-{[(l-ethylpyrrolidin-2- yl)carbonyl] oxy} butyl l-methylpyrrolidine-2 -carboxylate (and corresponding dimethiodide salt), 4-{[(l-butylpyrrolidin-2-yl)carbonyl]oxy}butyl 1-methylpyrrolidine- 2-carboxylate (and corresponding dimethiodide salt).

2. A compound according to Claim 1 in which the alkylene linker group is of formula -(CH₂)_n- in which n is an integer from 1 to 10.

3. A compound according to Claim 1 or 2 in which the nitrogen containing group is selected from:

(a) (b) (c) (d)

(e) (f) (g) (h) in which

R₃ and _t each independently is selected from hydrogen, -(C=NH)NH₂₎ Cι-C₄ -alkyl, C_2-6

-alkenyl and optionally substituted C _1-4-alkylphenyl; m is an integer selected from 0, 1 or 2; and

* signifies the point of attachment to the ester group.

4. A compound according to claim 1 which is a di-ester of Formula (I)

(I) wherein: n = integer from 1 to 10; and

Ri and R₂ each independently is selected from the preferred nitrogen containing groups

(a) (b) (c) (d)

(e) (f) (9) (h)

in which R3 and R₄ each independently is selected from hydrogen, -(C=NH)NH_2j Cι-C₄ -alkyl, C_2-6

* signifies the point of attachment to the ester group.

5. A compound according to claim 1 which is a di-ester of Formula (II)

(II) wherein: n = integer from 1, 2, 3, 4 or 5; and

(a) (b) (c) (d)

(e) (f) (9) (h)

in which

R₃ and R each independently is selected from hydrogen, -(C=NH)NH₂, C C₄ -alkyl, C_2-6

-alkenyl and optionally substituted C _1- -alkylphenyl; m is an integer selected from 0, 1 or 2; and

* signifies the point of attachment to the ester group.

6. A pharmaceutical composition comprising a compound as defined in any one of claims 1 to 5 and one or more pharmaceutically acceptable diluents or carriers.

7. A method of inducing neuromuscular paralysis in a mammal comprising administering to said mammal an effective neuromuscular blocking amount of a compound as defined in any one of claims 1 to 5 and one or more pharmaceutically acceptable diluents or carriers, or a pharmaceutical composition as defined in claim 6.

8. A compound as defined in any one of claims 1 to 5 or a pharmaceutical composition as defined in claim 6 for use in therapy.

9. A compound as defined in any one of claims 1 to 5 or a pharmaceutical composition as defined in claim 6 for use as a medicament for inducing neuromuscular blockade in a mammal.

10. Use of a compound as defined in any one of claims 1 to 5 or a pharmaceutical composition as defined in claim 6 for the manufacture of a medicament for inducing neuromuscular blockade in a mammal.