this invention relates to a compound and method for reducing neurotoxic effects ( such as seizures and brain damage ) caused by cholinergic agents such as soman ( a nerve gas ). effective treatment can be provided by administering an aryl - cycloalkylalkanolamine represented by formula i : ## str3 ## wherein r 1 is one or more groups independently selected from hydrido , halo , alkyl , acyl , hydroxyalkyl , haloalkyl , aminoalkyl , alkoxy , amino , alkylamino and acylamino ; wherein r 2 is selected from hydrido , cycloalkyl , cycloalkenyl , halocycloalkyl , alkylcycloalkyl , acylcycloalkyl , hydroxycycloalkyl , haloalkylcycloalkyl , aminoalkylcycloalkyl , alkoxycycloalkyl , aminocycloalkyl , bicycloalkyl , bicycloalkenyl and tricycloalkyl wherein the bicycloalkyl , bicycloalkenyl and tricycloalkyl groups may be substituted with one or more groups selected from alkyl , halo , acyl , hydroxy , hydroxyalkyl , haloalkyl , acyl , alkoxy , amino and alkylamino ; wherein each of r 3 and r 4 is independently selected from hydrido , alkyl , acyl , alkenyl , cycloalkyl , phenylalkyl , phenyl , aminoalkyl and alkylaminoalkyl ; and wherein r 3 and r 4 may be taken together to form a cyclic group including the nitrogen atom of formula i , and n is an integer selected from one through five . during the research which led to this invention , seizures and seizure - related brain damage caused by pilocarpine or soman were effectively prevented in vivo tests using lab animals , by administration of several representative compounds of formula i using the methods described in the examples . the compounds covered by formula i includes several compounds that are commercially available , including : α - cyclohexyl - α - phenyl - 1 - pyrrolidinepropanol ( common name &# 34 ; procyclidine &# 34 ;), which has the following structure : ## str4 ## α - cyclohexyl - α - phenyl - 1 - piperidinepropanol ( common name &# 34 ; trihexyphenidyl &# 34 ;), which has the following structure : ## str5 ## α - bicyclo [ 2 . 2 . 1 ] hept - 5 - en - 2 - yl - α - phenyl - 1 - piperidinepropanol ( common name &# 34 ; biperiden &# 34 ;), which has the following structure : ## str6 ## α - phenyl - α - tricyclo [ 2 . 2 . 1 . 02 , 6 ] hept - 3 - yl - 1 - piperidinepropanol ( common name &# 34 ; triperiden &# 34 ;) which has the following structure : ## str7 ## the following compounds also have chemical structures within the parameters described in formula i : any compound listed above may be tested by a routine screening process , as described in the examples , to assess the effectiveness of that particular compound against cholinergic toxins such as soman or pilocarpine . the term &# 34 ; hydrido &# 34 ; denotes a single hydrogen atom ( h ) which may be attached , for example , to a carbon atom or to an oxygen atom to form an hydroxyl group . the term &# 34 ; alkyl &# 34 ; embraces linear or branched radicals having one to about ten carbon atoms . the term &# 34 ; cycloalkyl &# 34 ; embraces radicals having three to about ten carbon atoms , such as cyclopropyl and cyclobutyl . the term &# 34 ; haloalkyl &# 34 ; embraces radicals wherein one or more of the alkyl carbon atoms is substituted with one or more halo groups , preferably selected from bromo , chloro and fluoro . dihaloalkyl and polyhaloalkyl groups may be substituted with two or more of the same halo groups , or may have a combination of different halo groups . the terms &# 34 ; alkylol &# 34 ; and &# 34 ; hydroxylalkyl &# 34 ; embrace linear or branched alkyl groups having one to ten carbon atoms , any one of which may be substituted with one or more hydroxyl groups . the term &# 34 ; alkenyl &# 34 ; embraces linear or branched radicals having two to about ten carbon atoms and containing at least one carbon - carbon double bond . the terms &# 34 ; alkoxy &# 34 ; and &# 34 ; alkoxyalkyl &# 34 ; embrace linear or branched oxy - containing radicals having alkyl portions of one to ten carbon atoms , such as methoxy group . the &# 34 ; alkoxy &# 34 ; or &# 34 ; alkoxyalkyl &# 34 ; radicals may be further substituted with one or more halo atoms , such as fluoro , chloro or bromo , to provide haloalkoxy or haloalkoxyalkyl groups . examples of other substituents forming compounds of formula i are as follows : ______________________________________substituent name structure______________________________________alkylcycloalkyl ## str8 ## acylcycloalkyl ## str9 ## halocycloalkyl ## str10 ## hydroxycycloalkyl ## str11 ## haloalkylcycloalkyl ## str12 ## aminoalkylcycloalkyl ## str13 ## bicycloalkyl ## str14 ## bicycloalkenyl ## str15 ## tricycloalkyl ## str16 ## ______________________________________ alkenyl and alkynyl groups may have one unsaturated bond , such as an allyl groups , or a plurality of unsaturated bonds , with such bonds adjacent , such as allene - type structures , in conjugation , or separated by several saturated carbons . included within the family of compounds of formula i , are the tautomeric forms of the described compounds , isomeric forms including diastereomers , and the pharmaceutically - acceptable salts thereof . the term &# 34 ; pharmaceutically - acceptable salts &# 34 ; embraces salts commonly used to form alkali metal salts and to form addition salts of free acids or free bases . since the compounds of formula i contain basic nitrogen atoms , such salts are typically acid addition salts . the nature of the salt is not critical , provided that it is pharmaceutically acceptable , and acids which may be employed to form such salts are well known to those skilled in this art . examples of acids which may be employed to form pharmaceutically acceptable acid addition salts include such inorganic acids as hydrochloric acid , sulphuric acid and phosphoric acid , and organic acids such as maleic acid , succinic acid and citric acid . other salts include salts with alkali metals or alkaline earth metals , such as sodium , potassium , calcium and magnesium . all of these salts may be prepared by conventional means from the corresponding compound of formula i by reacting , for example , the appropriate acid with the compound of formula i . methods of synthesis of representative compounds of formula i are known . for example , synthesis of procyclidine and its salts are shown in u . s . pat . nos . 2 , 891 , 890 and 2 , 826 , 590 . synthesis of trihexyphenidyl hydrochloride is described in u . s . pat . no . 2 , 682 , 543 . synthesis of biperiden is described in u . s . pat . no . 2 , 789 , 110 . administration of compounds within formula i to humans can be by any technique capable of introducing the compounds into the bloodstream of a human patient , including oral administration , and by intravenous , intramuscular and subcutaneous injections . the active compound is usually administered in a pharmaceutically - acceptable formulation , although in some acute - care situations a compound of formula i may be administered alone . such formulations may comprise the active compound together with one or more pharmaceutically - acceptable carriers or diluents . other therapeutic agents may also be present in the formulation . a pharmaceutically - acceptable carrier or diluent provides an appropriate vehicle for delivery of the active compound without introducing undesirable side effects . delivery of the active compound in such formulations may be by various routes including oral , nasal , topical , buccal and sublingual , or by parenteral administration such as subcutaneous , intramuscular , intravenous and intradermal routes . adult male sprague dawley rats ( 300 - 400 g ) were treated with lithium chloride ( 3 meq / kg subcutaneous ( sc )), to potentiate the pilocarpine effect and reduce individual variability among the rats . one day later the experimental group was treated with procyclidine ( 75 mg / kg intraperitoneal ( ip )). the control group was treated with an equivalent volume of saline . thirty minutes later , both groups received a single treatment with pilocarpine ( 30 mg / kg sc ). rats were observed over a 4 hour period for behavioral signs of neurotoxicity , including preconvulsive signs such as facial grimacing , head nodding , eye blinking , wet dog shakes , or evidence of convulsions , including rearing on hind limbs with clonic movements of the head and forelimbs . after 4 hours , they were anesthetized and perfused through the left cardiac ventricle and ascending aorta with an aldehyde fixative solution for 15 minutes , then the brains were removed from the skull and processed for histopathological evaluation by methods previously described for light and electron microscopy ( olney 1971 ). the results were as follows : all of the rats in the saline control group , i . e ., rats that received lithium / pilocarpine but not procyclidine , displayed the full behavioral syndrome of preconvulsive and convulsive symptoms with persistent seizure activity being present for the majority of the 4 hour observation period . all of these rats in the saline control group ( n = 6 ) had severe brain damage affecting the cerebral cortex , hippocampus , amygdala , piriform cortex , thalamus , lateral septum and substantia nigra . none of the treated rats ( lithium / pilocarpine and procyclidine ) displayed either preconvulsive or convulsive signs , and none ( n = 6 ) sustained brain damage . in a second experiment , all conditions were the same except that the procyclidine ( 75 mg / kg i . p .) or saline was not administered until 30 min after pilocarpine . all of the rats in the saline control group ( n = 6 ) exhibited a full behavioral syndrome , including persistent seizures and disseminated brain damage . most of the rats in the treatment group had begun to seize before procyclidine was administered , but all convulsive behavior disappeared within 10 minutes after procyclidine administration and all of these rats ( n = 6 ) escaped brain damage . prior research on receptor binding data had suggested that procyclidine interacts weakly with phencyclidine receptors ( olney et al 1987 ). in addition , recent research by the inventor of the subject application ( olney 1989 ) indicated that phencyclidine and mk - 801 can cause vascular cytopathological changes in the posterior cingulate and retrosplenial cerebral cortices . the correlation of those findings suggests that procyclidine might also cause some degree of pcp - like toxicity . to evaluate that possibility , the affected brain regions were examined in the rats ( n = 12 ) from the treatment groups in both of the experiments described above ( i . e ., rats that received procyclidine either before or after the pilocarpine ). there was no evidence of the vascular cytopathology that occurs following phencyclidine or mk - 801 treatment . a major problem in studying the soman cholinotoxic syndrome is the marked individual variation in sensitivity of experimental animals . some adult rats develop status epilepticus ( persistent seizures ) within 5 - 15 minutes after receiving a dose of soman in the range of 90 - 125 ug / kg ( micrograms / kilogram ) i . p . those animals typically sustain severe brain damage and die within 1 to 6 hours . however , other rats can tolerate much higher doses of soman without exhibiting seizures or brain damage and such animals survive treatment without any apparent untoward effects . administering lithium chloride 24 hours prior to soman causes a moderate , but consistent , increase in the percentage of animals susceptible to soman neurotoxicity . in a study to evaluate the possibility that procyclidine might protect against the neurotoxic effects of soman , adult male sprague dawley rats ( 350 - 425 g ) were pretreated with lithium chloride ( 3 mg / kg sc ) and 24 hrs later given soman ( 125 ug / kg sc ) and observed for symptoms . animals that began convulsing were treated immediately either with saline ( control group ) or a single dose ( 75 mg / kg i . p .) of procyclidine ( treatment group ). animals that did not convulse received no further treatment . all animals were anesthetized and killed 4 hours after soman treatment and their brains examined histologically by methods described above . rats that did not seize ( n = 28 ) did not have any brain pathology . all rats that seized and received saline ( n = 8 ) had severe disseminated brain damage . rats that seized and received procyclidine ( n = 12 ), stopped seizing within 5 to 15 minutes ; all of these rats escaped brain damage . in a separate experiment , atropine , which like procyclidine is classified as an anti - cholinergic drug , was substituted for procyclidine in the above protocol . at doses up to 100 mg / kg i . p ., atropine conferred no protection against soman neurotoxicity . in an additional experiment , the neuroprotective properties of procyclidine were exploited to establish a colony of rats selectively bred for increased susceptibility to soman neurotoxicity . adult male and female rats were challenged with soman . those that responded with seizures ( n = 8 ) were identified as soman - sensitive and were treated with procyclidine which protected them , allowing them to survive and serve as breeding stock . the first generation offspring of soman - sensitive male / female matings were challenged with soman and found to have a substantially increased rate of soman sensitivity ( increased from 40 % to 80 %), even though lithium pretreatment was not used . administration of procyclidine to these animals ( n = 8 ) when they started seizing , consistently caused cessation of seizures and protection against brain damage . thus , if experimental animals from the above studies are combined , the total number of rats protected against soman neurotoxicity by administration of procyclidine following onset of convulsive symptoms is 28 . although lithium pretreatment was employed in the first experiment , rats in the latter two experiments ( n = 16 ) received soman without lithium pretreatment . therefore , either in the presence or absence of lithium , procyclidine provides effective protection against soman neurotoxocity . preliminary tests using a small number of rats were performed to determine whether biperiden or trihexyphenidyl were effective against a cholinergic neurotoxin . rats were subjected to lithium priming and pilocarpine exposure as described in example 2 , and rats that showed seizure activity were treated with either biperiden or trihexyphenidyl . in all such rats , seizure activity ceased , and histological examination did not indicate any brain damage . although this invention has been described with respect to specific embodiments , the details of these embodiments are not to be construed as limitations . various equivalents and modifications may be made without departing from the spirit and scope of this invention , which is limited only by the claims which follow . anis , n . a . et al , &# 34 ; the dissociative anaesthetics , ketamine and phencyclidine , selectively reduce excitation of central mammalian neurons by n - methyl - asparate &# 34 ;, br . j . pharmacol . 79 : 565 ( 1983 ). berry , s . d ., et al , &# 34 ; stereoselective effects of two phencyclidine derivatives on n - methylaspartate excitation of spinal neurones in the cat and rat &# 34 ;, eur . j . pharm . 96 : 261 ( 1983 ). braitman , d . j ., et al , &# 34 ; mk - 801 protects against seizures and brain damage induced by the cholinesterase inhibitor soman ,&# 34 ; neurosci . abstr . 14 : 240 ( 1988 ). clifford , d . b ., et al , &# 34 ; effect of anti - convulsant drugs on kainic acid induced epileptiform activity ,&# 34 ; exp . neurol . 76 : 156 ( 1982 ). clifford d . b ., olney , j . w ., maniotis , a ., collins , r . c . and zorumski , c . f . &# 34 ; the functional anatomy and pathology of lithium - pilocarpine and high - dose pilocarpine seizures .&# 34 ; neurosci . 23 : 953 - 968 ( 1987 ). fleischhacker , w . w ., et al , j . affective disorder 12 ( 2 ): 153 - 157 ( 1987 ). fuller , t . a . and olney , j . w ., &# 34 ; only certain anti - convulsants protect against kainic acid neurotoxocity ,&# 34 ; neurobiol . toxicol . and teratol . 3 : 355 - 361 ( 1981 ). goldman , m . e ., et al , &# 34 ; differentiation of [ 3 h ] phencyclidine and (+)-[ 3 h ] skf - 10 , 047 binding sites in rat cerebral cortex &# 34 ;, febs lett . 170 : 333 - 336 ( 1985 ). goodman , l . s . and gilman , a ., the pharmacological basis of therapeutics , 5th ed ., ( macmillan , ny , 1975 ). honchar , m . p ., olney , j . w . and sherman , w . r ., &# 34 ; systemic cholinergic agents induce seizures and brain damage in lithium - treated rats ,&# 34 ; science 220 : 323 - 325 ( 1983 ). labruyere , j ., et al , &# 34 ; phencyclidine and ketamine protect against seizure - related brain damage ,&# 34 ; neurosci . abstr . 12 : 344 ( 1986 ). lawrence , j . j ., fuller , t . a ., and olney , j . w ., &# 34 ; mk - 801 and pcp protect against ischemic neuronal degeneration in the gerbil hippocampus ,&# 34 ; neurosci . abstr . 13 : 1079 ( 1987 ). mann , n ., et al , arch . pharm . ( weinheim , ger .) 309 ( 4 ): 320 - 325 ( 1976 ). maragos , w ., et al , &# 34 ; high correlation between the localization of [ 3 h ] tcp binding and nmda receptors ,&# 34 ; eur . j . pharmacol . 123 : 173 - 174 ( 1986 ). mcleod , c . g ., et al , &# 34 ; acute neuropathology in soman - poisoned rats ,&# 34 ; neurotoxicology 5 : 53 - 58 ( 1984 ). olney , j . w ., &# 34 ; glutamate - induced neuronal necrosis in the infant mouse hypothalamus : an electron microscopic study ,&# 34 ; j . neuropathol . exp . neurol . 30 : 75 - 90 ( 1971 ). olney , j . w ., &# 34 ; excitotoxins : an overview ,&# 34 ; in excitotoxins , fuxe , k ., et al , eds . ( macmillan , london ) pp 82 - 96 ( 1983 ). olney , j . w ., et al , &# 34 ; the anti - excitotoxic effects of certain anesthetics , analgesics and sedative hypnotics ,&# 34 ; neuroscience letters 68 : 29 - 34 ( 1986 ). olney , j . w ., et al , &# 34 ; anti - parkinsonian agents are phencyclidine agonists and n - methyl aspartate antagonists ,&# 34 ; eur . j . pharmacol . 142 : 319 - 320 ( 1987 ). olney , j . w ., et al , &# 34 ; mk - 801 prevents hypobaric - ischemic neuronal degeneration in infant rat liver ,&# 34 ; j . neurosci . 9 : 1701 ( 1989 ). olney , j . w ., et al , &# 34 ; pathological changes induced in cerebrocortical neurons by phencyclidine and related drugs .&# 34 ; science 244 : 1360 - 1362 ( 1989 ). quirion , r ., &# 34 ; phencyclidine ( angel dust )/ sigma opiate &# 39 ; receptor : visualization by tritium - sensitive film ,&# 34 ; proc . nat &# 39 ; l . acad . sci . u . s . a . 78 : 5881 ( 1981 ). rothman , s . m ., and olney , j . w ., &# 34 ; glutamate and the pathophysiology of hypoxia - ischemic brain damage ,&# 34 ; annals of neurology 19 ( 2 ): ( 1986 ). snell , l . d ., et al , &# 34 ; antagonism of nmda - induced transmitter release in the rat striatum by phencyclidine - like drugs and its relationship to turning behavior ,&# 34 ; j . pharmacol . exp . ther . 235 : 50 - 56 , ( 1985 ). syvalahti , e . k . g ., et al , pharmacol . toxicol . ( copenhagen ) 60 ( 1 ): 66 - 69 ( 1987 ). wong , e . h . f ., et al , &# 34 ; the anticonvulsant mk - 801 is a potent n - methyl - d - aspartate antagonist ,&# 34 ; proc . nat &# 39 ; l . acad . sci u . s . a . 83 : pp . 7104 - 7108 ( september 1986 ).
a compound and method are disclosed for reducing neurotoxic effects caused by cholinergic agents such as soman and pilocarpine . effective treatment can be provided by administering an aryl - cycloalkylalkanolamine substance having the general formula : ## str1 ## the compoudns procyclidine , biperiden , and trihexyphenidyl fall within this class of compounds . although not previously recognized to be effective against soman or other cholinergic neurotoxins , all three representative compounds have been discovered to be highly effective against all cholinergic neurotoxins tested to data , even when administered after actual seizures begin .