Abstract:
The invention relates to novel substituted 2,3-dihydro-5-(3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acids, their derivatives and their salts. The compounds are useful for the treatment and prevention of injury to the brain and of edema due to head trauma, stroke (particularly ischemic), arrested breathing, cardiac arrest, Reye&#39;s syndrome, cerebral thrombosis, cerebral embolism, cerebral hemorrhage, cerebral tumors, encephalomyelitis, spinal cord injury, hydrocephalus, post-operative brain injury trauma, edema due to cerebral infections and various brain concussions.

Description:
BACKGROUND OF THE INVENTION 
     Trauma to the brain or spinal cord caused by physical forces acting on the skull or spinal column, by ischemic stroke, arrested breathing, cardiac arrest, Reye&#39;s syndrome, cerebral thrombosis, cerebral embolism, cerebral hemorrhage, encephalomyelitis, hydrocephalus, post-operative brain injury, cerebral infections and various concussions results in edema and swelling of the affected tissues. This is followed by ischemia, hypoxia, necrosis, temporary or permanent brain and/or spinal cord injury and may result in death. The tissue mainly affected are classified as grey matter, more specifically astroglial cells. The specific therapy currently used for the treatment of the medical problems described include various kinds of diuretics (particularly osmotic diuretics), steroids (such as, 6-α-methylprednisolone succinate) and barbiturates. The usefulness of these agents is questionable and they are associated with a variety of untoward complications and side effects. Thus, the compounds of this invention comprise a novel and specific treatment of medical problems where no specific therapy is available. 
     A recent publication entitled &#34;Agents for the Treatment of Brain Injury&#34; 1. (Aryloxy)alkanoic Acids, Cragoe et al, J. Med. Chem., (1982) 25, 567 -79, reports on recent experimental testing of agents for treatment of brain injury and reviews the current status of treatment of brain injury. 
     Some 2-benzofurancarboxylic acids have been reported to be diuretic and saluretic agents in U.S. Pat. Nos. 3,843,797; 3,761,494; 3,751,436; 3,751,430, 3,726,904; 3,723,619; 3,709,909; 3,682,961; 3,681,502; 3,676,560; 3,674,810; 3,651,094; 3,627,785; 3,580,931; 3,574,208 and 3,557,152 of Habicht et al. Additionally, E. J. Cragoe, Jr., Diuretics: Chemistry, Pharmacology and Medicine (1983) p. 220 as well as, U.S. Pat. Nos. 4,085,117; 4,087,542; 4,100,294; 4,154,742; 4,163,794; 4,181,727; 4,237,144; 4,296,122 and 4,401,669 of E. J. Cragoe, Jr. et al. disclosed that the 6,7-dichloro derivatives of these compounds also have activity as diuretics. There is, however, no suggestion in the patents or publication that any of the compounds disclosed therein would be of use in the treatment of brain injury. 
     The compounds of the invention have the added advantage of being devoid of the pharmacodynamic, toxic or various side effects characteristic of the diuretics, steroids and barbiturates. 
     DESCRIPTION OF THE INVENTION 
     The compounds of the instant invention are best characterized by reference to the following structural Formula (I): ##STR1## wherein: R is hydroxyl, lower alkoxy, branched or unbranched, containing from 1 to 5 carbon atoms such as methoxy, ethoxy, n-propoxy, isopropoxy and the like, carboxyalkoxy group containing from 2 to 6 carbon atoms such as carboxymethoxy, 1 carboxyethoxy, 1-carboxy-1-methylthoxy, 2-carboxyethoxy, 1-carboxy-1-ethylpropyl and the like dialkylaminoalkoxy containing from 4 to 7 carbon atoms, amino, alkylamino containing from 1 to 4 carbon atoms, dialkylamino containing from 2 to 6 carbon atoms, or dialkylaminoalkylamino containing from 4 to 7 carbon atoms; 
     R 1  is hydrogen or lower alkyl, branched or unbranched, containing from 1 to 5 carbon atoms; 
     R 2 , R 3  are each independently hydrogen, lower alkyl, branched or unbranched, containing from 1 to 5 carbon atoms, cycloalkyl containing from 3 to 6 nuclear carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl and the like, or aryl such as phenyl; 
     R 4 , R 5  are each independently hydrogen, lower alkyl, branched or unbranched, containing from 1 to 5 carbon atoms, aralkyl such as benzyl, aryl such as phenyl, or halo substituted aryl such as p-fluorophenyl, o-fluorophenyl, p-chlorophenyl and the like; 
     R 6  is hydrogen, lower alkyl, branched or unbranched, containing from 1 to 5 carbon atoms, an alkoxycarbonyl group containing from 2 to 6 carbon atoms, a carbamoyl group such as N-alkylcarbamoyl of 1 to 4 carbon atoms or N,N-dialkylcarbamoyl containing 2 to 6 carbon atoms; and 
     X, Y are each independently hydrogen, halo or lower alkyl containing from 1 to 5 carbon atoms. 
     Positions-4,5 and 6 of the cyclohexene ring when occupied by two different groups and position-2 of the 2,3-dihydrobenzofuran ring are asymmetric, therefore the compounds of the invention exhibit optical isomerism. If there is only one asymmetric atom, the product consists of a racemate composed of two enantiomers. If there are two asymmetric atoms, there will be two diasteriomers, each consisting of a racemate. Diasteriomers can be separated by physical means, e.g. chromatography. Racemic compounds or their precursors can be resolved so that the pure enantiomers can be prepared, thus the invention includes each pure diasteriomer and the corresponding pure enantiomers. This is an important point since some of the racemic diasteriomers consist of one racemate which is much more active than the other one and the same is true of the two enantiomers of each racemic diasteromer. Furthermore, the less active diasteromer or enantiomer generally possesses the same intrinsic toxicity as the more active diasteriomer or enantiomer. In addition, it can be demonstrated that the less active diasteriomer or enantiomer depresses the inhibitory action of the active enantiomer at the tissue level. Thus, for three reasons it is advantageous to use the pure, more active diasteriomer or enantiomer rather than the mixed diasteriomers or racemate. 
     Since the carboxylic acid products of the invention are acidic, the invention also includes the obvious pharmaceutically acceptable salts, such as the sodium, potassium, ammonium, trimethylammonium, piperazinium, 1-methylpiperazinium, guanidinium, bis-(2-hydroxethyl)ammonium, N-methylglucosammonium and the like salts. 
     It is also to be noted that the compounds of Formula I, as well as their salts, often form solvates with the solvents in which they are prepared or from which they are recrystallized These solvates may be used per se or they may be desolvated by heating (e.g. at 70° C.) in vacuo. 
     Although the invention primarily involves novel substituted 2,3-dihydro-5-(3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acids and their salts, it also includes their derivatives, such as esters, amides, oximes, hydrazones and the like. Additionally, this invention includes pharmaceutical compositions in unit dosage form containing a pharmaceutical carrier and an effective amount of a compound of Formula I, its pure diasteriomer or its pure (-) or (+) enantiomer, or the pharmaceutically acceptable salts thereof, for treating brain injury. The method of treating a person with brain injury by administering said compounds or said pharmaceutical compositions is also a part of this invention. 
     PREFERRED EMBODIMENT OF THE INVENTION 
     The preferred embodiments of the instant invention are realized in structural Formula II: ##STR2## wherein: R 1 , R 3 , R 4 , R 5 , R 6  are each independently hydrogen or lower alkyl containing from 1 to 5 carbon atoms. 
     Also included are the diasteriomers and the enantiomers of each racemate. 
     A preferred compound, is 6,7-dichloro-2,3-dihydro-5-(6-ethyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid, its pure diasteriomers, their pure (+) and (-)-enantiomers and their salts. 
     Another preferred compound is 6,7-dichloro-2,3-dihydro-5-(5-methyl-3-oxo-2-cylcohexen-1-yl)-2-benzofurancarboxylic acid, its pure diasteriomers, their pure (+) and (-) enantiomers and their salts. 
     Another preferred compound is 1-carboxy1-methylethyl 6,7-dichloro-2,3-dihydro-5-(5-methyl-3- oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylate, its pure diasteriomers, their (+) and (-) enantiomers and their salts. 
     Especially preferred are the pure enantiomers since, in most instances, one enantiomer is more active biologically then its antipode. 
     Included within the scope of this invention are the pharmaceutically acceptable salts of substituted 2,3-dihydro-5-(3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acids since a major medical use of these compounds is solutions of their soluble salts which can be administered parenterally. 
     Thus, the salts can be prepared by the reaction of the substituted 2,3-dihydro-5-(3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acids of this invention with an appropriate amine, ammonium hydroxide, guanidine, alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate, quaternary ammonium hydroxide and the like. The salts selected are derived from among the non-toxic, pharmaceutically acceptable bases. 
     The synthesis of the substituted 2,3-dihdyro-5-(3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acids of formula I are generally carried out by the following route illustrated by the preparation of 6,7-dichloro-2,3-dihydro-5-(6-ethyl-3-oxo-2- cyclohexen-1-yl)-2-benzofurancarboxylic acid (IIA). 
     The starting material ethyl 6,7-dichloro-2,3-dihydro-2-benzofurancarboxylate (III) is acylated to form 5-butyryl-6,7-dichloro-2,3-dihydro-2-benzofurancarboxylic acid (IV) in a Friedel-Crafts acylation reaction using aluminum chloride and butyryl chloride (Step A). This material is reacted with dimethylamine hydrochloride and formaldehyde in a Mannich Reaction which following deamination yields 6,7-dichloro-2,3-dihydro-5-(2-methylenebutyryl)-2-benzofurancarboxylic acid (V) (Step B). The material formed in Step B is then subjected to a Michael addition and an aldol condensation with acetoacetic ester, which following decarboxylation yields 6,7-dichloro-2,3-dihydro-5-(6-ethyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid (Step C). The starting material used in these examples is obtained as shown in the Journal of Medicinal Chemistry, 24, 865-873 (1981). This synthetic route is illustrated below: ##STR3## 
     By selecting the appropriately substituted compound of the type illustrated by Formula IIIA, one can obtain products of Formula I with the desired X and Y substituents. By selecting the appropriate acyl halide (VI) one can obtain a product of Formula I with the desired R 3  substituent. By using the appropriately substituted acetoacetic ester (VII) or acetoacetamide (VIII) to react with the intermediate of Formula VA, one obtains a product with the desired substituents at R 1  and R 6 . To obtain a product of Formula I with the appropriate R 4  and R 5  substituents, one uses the appropriate intermediate of Formula VB to react with VII or VIII. This is illustrated as follows: ##STR4## 
     It should be noted that when a product of Formula I is desired wherein R 2  and R 3  are H the required intermediate is the intermediate Mannich (IX) rather that (VC) (which is generated in situ). ##STR5## 
     Those compounds possessing an asymmetric carbon atom at the 2-position of the 2,3-dihydrobenzofuran ring and the 4-position of the cyclohexene ring consist of two diasteriomers, each of which consist of a racemate composed of two enantiomers. The diasteriomers can be separated into two pure racemates by chromatography. The resolution of each racemate may be accomplished by forming a salt of the racemic mixture with an optically active base such as (+) or (-)amphetamine, (-)cinchonidine, dehydroabietylamine, (+) or (-)-α-methylbenzylamine, (+) or (-)(1-naphthyl)ethylamine (+) cinchonine, brucine, or strychnine and the like in a suitable solvent such as methanol, ethanol, 2-propanol, benzene, acetonitrile, nitromethane, acetone and the like. There is formed in the solution, two diastereomeric salts, one of which is usually less soluble in the solvent than the other. Repetitive recrystallization of the crystalline salt generally affords a pure diastereomeric salt from which is obtained the desired pure enantiomer. The optically pure enantiomer of the compound of Formula I is obtained by acidification of the salt with a mineral acid, isolation by filtration and recrystallization of the optically pure antipode. 
     The other optically pure antipode may generally be obtained by using a different base to form the diastereomeric salt. It is of advantage to isolate the partially resolved acid from the filtrates of the purification of the first diastereomeric salt and to further purify this substance through the use of another optically active base. It is especially advantageous to use an optically active base for the isolation of the second enantiomer which is the antipode of the base used for the isolation of the first enantiomer. For example, if (+)-α-methylbenzylamine was used first, then (-)-α-methylbenzylamine is used for the isolation of the second (remaining) enantiomer. 
     The salts are prepared by reacting the acids of Formula I with an appropriate base, for example, alkali metal or alkaline earth bicarbonate, carbonate or alkoxide, an amine, ammonia, an organic quaternary ammonium hydroxide, guanidine and the like. 
     The reaction is generally conducted in water when alkali metal hydroxides are used, but when alkoxides and the organic bases are used, the reaction may be conducted in an organic solvent, such as ether, ethanol, dimethylformamide and the like. 
     The preferred salts are the pharmaceutically acceptable salts such as sodium, potassium, ammonium and the like. 
     The ester and amide derivatives of the 2-position carboxylic acid compounds are made from the carboxylic acid which is converted to the carbonyl-1-imidazole derivative by reaction with carbonyl diimidazole. This compound is then reacted with the appropriate alcohol or amine to obtain the desired ester or amide. 
     Inasmuch as there are a variety of symptoms and severity of symptoms associated with grey matter edema, particularly when it is caused by head trauma, stroke, cerebral hemorrhage or embolism, post-operative brain surgery trauma, spinal cord injury, cerebral infections and various brain concussions, the precise treatment is left to the practioner. Generally, candidates for treatment will be indicated by the results of the patient&#39;s initial general neurological status, findings on specific clinical brain stem functions and findings on computerized axial tomography (CAT), nuclear magnetic resonance (NMR) or positron emission tomography (PET) scans of the brain. The sum of the neurological evaluation is presented in the Glascow Coma Score or similar scoring system. Such a scoring system is often valuable in selecting the patients who are candidates for therapy of this kind. 
     The compounds of this invention can be administered by a variety of established methods, including intravenously, intramuscularly, subcutaneously, or orally. The parenteral route, particularly the intravenous route of administration, is preferred, especially for the very ill and comatose patient. Another advantage of the intravenous route of administration is the speed with which therapeutic brain levels of the drug are achieved. It is of paramount importance in brain injury of the type described to initiate therapy as rapidly as possible and to maintain it through the critical time periods. For this purpose, the intravenous administration of drugs of the type of Formula I in the form of their salts is superior. 
     A recommended dosage range for treatment is expected to be from 0. 05 mg/kg to 50 mg/kg of body weight as a single dose, preferably from 0.5 mg/kg to 20 mg/kg. An alternative to the single dose schedule is to administer a primary loading dose followed by a sustaining dose of half to equal the primary dose, every 4 to 24 hours. When this multiple dose schedule is used the dosage range may be higher than that of the single dose method. Another alternative is to administer an ascending dose sequence of an initial dose followed by a sustaining dose of 1 1/2 to 2 times the initial dose every 4 to 24 hours. For example, 3 intravenous doses of 8, 12 and 16 mg/kg of body weight can be given at 6 hour intervals. If necessary, 4 additional doses of 16 mg/kg of body weight can be given at 12 hour intervals. Another effective dose regimen consists of a continuous intravenous infusion of from 0.05 mg/kg/hr to 3.0 mg/kg/hr. Of course, other dosing schedules and amounts are possible. 
     One aspect of this invention is the treatment of persons with grey matter edema by concomitant administration of a compound of Formula I or its salts, and an antiinflammatory steroid. These steroids are of some, albeit limited, use in control of white matter edema associated with ischemic stroke and head injury. Steroid therapy is given according to established practice as a supplement to the compound of Formula I as taught elsewhere herein. Similarly, a barbiturate may be administered as a supplement to treatment with a compound of Formula I. 
     The compounds of Formula I are utilized by formulating them in a pharmaceutical composition such as tablet, capsule or elixir for oral administration. Sterile solutions or suspensions can be used for parenteral administration. A compound or mixture of compounds of Formula I, or its physiologically acceptable salt, is compounded with a physiologically acceptable vehicle, carrier, excipient, binder, preservative, stabilizer, flavor, etc. in a dosage form as called for by accepted pharmaceutical practice. 
     Illustrative of the adjuvants which may be incorporated in tablets, capsules and the like are the following: a binder such as gum tragacanth, acacia, corn starch or gelatin; an excipient such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; a sweetening agent such as sucrose, lactose, or saccharin; a flavoring agent such as peppermint, oil of wintergreen or cherry. When the dosage unit form is a capsule, it may contain in addition to materials of the above type a liquid carrier such as a fatty oil. Various other materials may be present as coatings or to otherwise enhance the pharmaceutical elegance of the preparation. For instance, tablets may be coated with shellac, sugar or the like. A syrup or elixir may contain the active compound, sucrose as a sweetening agent, methyl and propyl parabens as preservatives, a dye and a flavoring such as cherry or orange flavor. 
     Sterile compositions for injection or infusion can be formulated according to conventional pharmaceutical practice by dissolving the active substance in a conventional vehicle such as water, saline or dextrose solution by forming a soluble salt in water using an appropriate base, such as a pharmaceutically acceptable alkali metal hydroxide, alkali metal bicarbonate, ammonia, amine or guanidine. Alternatively, a suspension of the active substance in a naturally occurring vegetable oil like sesame oil, coconut oil, peanut oil, cottonseed oil, etc., or a synthetic fatty vehicle like ethyl oleate or the like may be formulated for injection or infusion. Buffer, preservatives, antioxidants and the like can be incorporated as required. 
     The basic premise for the development of agents for the treatment of brain injury of the types described is based on the studies in experimental head injury by R. S. Bourke et. al. (R. S. Bourke, M. A. Daze and H. K. Kimelberg, Monograph of the International Glial Cell symposium, Leige, Bel. August 29-31, 1977 and references cited therein) and experimental stroke by J. H. Garcia et. al. (J. H. Garcia, H. Kalimo, Y. Kamijyo and B. F. Trump, Virchows Archiv. [Zellopath.], 25, 191 (1977). 
     These and other studies have shown that the primary site of traumatic brain injury is in the grey matter where the process follows a pattern of insult, edema, ischemia, hypoxia, neuronal death and necrosis followed, in many instances, by irreversible coma or death. The discovery of a drug that specifically prevents the edema would obviate the sequalae. 
     Experimental head injury has been shown to produce a pathophysiological response primarily involving swelling of astroglial as a secondary, inhibitable process. At the molecular level, the sequence appears to be: trauma, elevation of extracellular K +  and/or release of neurotransmitters, edema, hypoxia and necrosis. Astroglial swelling results directly from a K +  -dependent, cation-coupled, chloride transport from the extracellular into the intracellular compartment with a concommitant movement of an osmotic equivalent of water. Thus, an agent that specifically blocks chloride transport in the astroglia is expected to block the edema caused by trauma and other insults to the brain. It is also important that such chloride transport inhibitors be free or relatively free of side effects, particularly those characteristics of many chloride transport inhibitors, such as diuretic properties. Compounds of the type illustrated by Formula I exhibit the desired effects on brain edema and are relatively free of renal effects. 
     That this approach is valid has been demonstrated by the correlation of the in vitro astroglial edema inhibiting effects of chloride transport inhibitors with their ability to reduce the mortality of animals receiving experimental in vivo head injury. As a final proof, one compound (ethacrynic acid) which exhibited activity both in vitro and in vivo assays was effective in reducing mortality in clinical cases of head injury. These studies are described in the Journal of Medicinal Chemistry, Volume 25, page 567 (1982), which is hereby incorporated by reference. 
     Three major biological assays can be used to demonstrate biological activity of the compounds. The (1) in vitro cat cerebrocortical tissue slice assay, (2) the in vitro primary rat astrocyte culture assay and (3) the in vivo cat head injury assay. The first assay, the in vitro cat cerebrocortical tissue slice assay has been described by Marshall, L. F.; Shapiro, H. M.; Smith, R. W. In &#34;Seminars in Neurological Surgery: Neural Trauma&#34;; Popp, A. J.; Bourke, R. S.; Nelson, L. R. ; Kimelberg, H, K,. Eds.; Raven Press: New York, 1979; p. 347, by Bourke, R. S.; Kimelberg, H, K.; Daze, M. A. in Brain Res. 1978, 154, 196, and by Bourke, R. S.; Kimelberg, H. K,; Nelson, L. R. in Brain Res. 1976, 105, 309. This method constitutes a rapid and accurate method of determining the intrinsic chloride inhibitory properties of the compounds of the invention in the target tissue. 
     The second assay method involves the in vitro primary rat astrocyte assay. The method has been described by Kimelberg, H. K.; Biddlecome, S.; Bourke, R. S. in Brain Res. 1979, 173, 111, by Kimelberg, H. K.; Bowman, c.; Biddlecome, S.; Bourke, R. S., in Brain Res. 1979, 177, 533, and by Kimelberg, H. K.; Hirata, H. in Soc. Neurosci. Abstr. 1981, 7, 698. This method is used to confirm the chloride transport inhibiting properties of the compounds in the pure target cells, the astrocytes. 
     The third assay method, the in vivo cat head injury assay has been described by Nelson, L. R.; Bourke, R. S.; Popp, A. J.; Cragoe, E. J. Jr.; Signorelli, A.; Foster, V. V. ; Creel, in Marshall, L. F.; Shapiro, H. M.; Smith, R. W. In &#34;Seminars in Neurological Surgery: Neural Trauma&#34;; Popp, A. J.; Bourke, R. S.; Nelson, L. R.; Kimelberg, H. K., Eds.; Raven Press: New York, 1979; p. 297. 
     This assay consists of a highly relevant brain injury in cats which is achieved by the delivery of rapid repetitive acceleration-deceleration impulses to the animal&#39;s head followed by exposure of the animals to a period of hypoxia. The experimental conditions of the assay can be adjusted so that the mortality of the control animals falls in the range of about 25 to 75%. Then, the effect of the administration of compounds of this invention in reducing the mortality over that of the control animals in concurrent experiments can be demonstrated. 
     Using the in vitro cat cerebrocortical tissue slice assay, described in Example 1, compounds of the present invention exhibited marked activity. This test provided the principal in vitro evaluation and consisted of a determination of concentration vs. response curve. The addition of HCO 3   -   to isotonic, K +  -rich saline-glucose incubation media is known to specifically stimulate the transport of Cl 31  coupled with Na +   and an osmotic equivalent of water in incubating slices of mammalian cerebral cortex. Experiments have demonstrated that the tissue locus of swelling is an expanded astroglial compartment. Thus, the addition of HCO 3   -  to incubation media stimulated statistically significant and comparable increases in cerebrocortical tissue swelling and ion levels. After addition of drug to the incubation media, detailed drug concentration-response curves were then obtained. The data were expressed as percent HCO 3   -  -stimulated swelling vs. drug concentration, from which the concentration of drug providing 50% inhibition of HCO 3   -  -stimulated swelling (I 50  in molarity) was interpolated. The results which are illustrative of compounds of the present invention are expressed in Table I, below: 
     
                       TABLE I______________________________________             I.sub.50, M______________________________________6,7-dichloro-2,3-dihydro-               10.sup.-85-(6-ethyl-3-oxo-2-cyclo-hexen-1-yl)-2-benzofuran-carboxylic acid______________________________________ 
    
     Thus, in the in vitro assay compounds of Formula I inhibit chloride transport by 50% at concentrations as low as 10 -8  molar. 
    
    
     The following examples are included to illustrate the in vitro cerebrocortical tissue slice assay, the preparation of representative compounds of Formula I and representative dosage forms of these compounds. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims. 
     EXAMPLE 1 
     In Vitro Cerebrocortical Tissue Slice Assay 
     Adult cats of 2 -3 kg body weight were employed in tissue slice studies. Prior to sacrifice, the animals were anesthetized with ketamine hydrochloride (Ketaset), 10 mg/kg im. Eight (three control, five experimental) pial surface cerebrocortical tissue slices (0.5-mm thick; approximately 150 mg initial fresh weight) were cut successively with a calibrated Stadie-Riggs fresh tissue microtome without moistening and weighed successively on a torsion balance. During the slice preparation all operations except weighing were confined to a humid chamber. Each slice was rapidly placed in an individual Warburg flask containing 2 ml of incubation medium at room temperature. The basic composition of the incubation media, in millimoles per liter, was as follows: glucose, 10; CaCl 2 , 1.3; MgSO 4 , 1.2; KHSO 4 , 1.2; Hepes (N-2-hydroxyethylpiperazine-N&#39;-2-ethanesulfonic acid, titrated with NaOH to pH 7.4), 20. Except when adding HCO 3   - , the osmolarity of the media was maintained isosmotic (approximately 285 mOsm/L) by reciprocal changes of Na +  or K +  to achieve a concentration of K 30   of 27 mM. The basic medium was bubbled for 30 minutes with 100% O 2  before use. When added, NaHCO 3  or triethylammonium bicarbonate (TEAB) was initially present in the sidearm of each flask at an initial concentration of 50 mM in 0.5 ml of complete medium. Nonbicarbonate control slices were incubated at 37°  C. in 2.5 ml of basic medium for 60 minutes. Bicarbonate control slices were similarly incubated for an initial 20 minutes at 37° C. in 2.0 ml of basic medium to which was added from the sidearm an additional 0.5 ml of incubation medium containing 50 mM HCO 3   - , which, after mixing, resulted in a HCO 3   -   concentration of 10 mM and a total volume of 2.5 ml. The incubation continued for an additional 40 minutes. The various compounds tested were dissolved by forming the sodium salts by treatment with a molar equivalent of NaHCO3 and diluting to the appropriate concentrations. Just prior to incubation, all flasks containing HCO 3   -  were gassed for 5 minutes with 2.5% CO 2  /97.5% O 2  instead of 100% O 2  . 
     Following the 60-minute incubation period, tissue slices were separated from incubation medium by filtration, reweighed, and homogenized in 1N HCLO10 4  (10% w/v) for electrolyte analysis. The tissue content of ion is expressed in micromoles per gram initial preswelling fresh weight. Control slice swelling is expressed as microliters per gram initial preswelling fresh weight. The effectiveness of an inhibitor at a given concentration was measured by the amount of HCO 3   -  -stimulated swelling that occurred in its presence, computed as a percent of the maximum possible. Tissue and media Na +  and K +  were determined by emission flame photometry with Li +   internal standard; C -   was determined by amperometric titration. Tissue viability during incubation was monitored by manometry. 
     EXAMPLE 2 
     Preparation of 6,7-dichloro-2,3-dihydro-5-(6-ethyl-3- oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid 
     Step A: 5-Butyryl-6,7-dichloro-2,3-dihydro-2-benzofurancarboxylic acid 
     To a stirred solution of ethyl 6,7-dichloro-2,3-dihydro-2-benzofurancarboxylate (13.4 g, 0.05 mole) and butyryl chloride (10 ml, 0.09 mole) in CH 2  Cl  2  (30 ml) cooled to 5° C. in an ice bath was added aluminum chloride (22.5 g, 0.17 mole) over a 10 minute period. The reaction mixture was stirred for 1 hour at 25° C. then for 20 minutes at reflux. The reaction mixture was poured into ice water, extracted into ether, washed with water and the ether evaporated in vacuo. The residue was treated with 10 N sodium hydroxide (100 ml) and the resultant sodium salt filtered and suspended in dilute hydrochloric acid which was extracted with ether (206 ml), washed with water, dried over magnesium sulfate, evaporated to 50 ml and treated with hexane to give 12.0 g of 5-butyryl-6,7-dichloro-2,3-dihydro-2-benzofurancarboxylic acid which melted at 124°-125° C. 
     Analysis for C 13  H 12  Cl 20  O 4  : Calc&#39;d: C, 51.51; H, 3.96. Found: C, 51.35; H, 3.83. 
     Step B: 6,7-Dichloro-2,3-dihydro-5(2-methylenebutyryl)-2-benzofurancarboxylic acid 
     A stirred mixture of 5-butyryl-6,7-dichloro-2,3-dihydro-2-benzofurancarboxylic acid (12.0 g, 0.04 mole), dimethylamine hydrochloride (4.3 g, 0.052 mole), para-formaldehyde (1.9 g, 0.063 mole) and acetic acid (4 drops) was heated on a steam bath for 21/2 hours. Dimethylformamide (35 ml) was added and heating was continued for 11/2 hours. The reaction mixture was poured into ice water, extracted with ether, washed with water and dried over magnesium sulfate. The ether was evaporated in vacuo and the residue triturated with butyl chloride (100 ml) to give 9.0 g of 6,7-dichloro-2,3-dihydro-5-(2-methylenebutyryl)-2-benzofurancarboxylic acid which melted at 148° C. 
     Analysis for C 14  H 12  Cl 2  O 4  : Calc&#39;d: C, 53.35; H, 3.84. Found: C, 53.39; H, 3.86. 
     Step C: 6,7-Dichloro-2,3-dihydro-5-(6-ethyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid 
     To a stirred refluxing solution of ethyl acetoacetate (2.9 g, 0.022 mole) and sodium methoxide (1.2 g, 0.022 mole) in ethanol (50 ml) was added 6,7-dichloro-2,3-dihydro-5-(2-methylenebutyryl)-2-benzofurancarboxylic acid (3.0 g, 0.01 mole). Refluxing was continued for 3 hours, the ethanol was distilled in vacuo and the residue was treated with ether and diluted hydrochloric acid. The ether was washed with water, dried over magnesium sulfate, and evaporated in vacuo. Trituration of the residue with butyl chloride gave 0.8 g of 6,7-dichloro-2,3-dihydro-5-(6-ethyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid which melted at 190°-192° C. 
     Analysis for C 17  H 16  Cl 2  O 2  : Calc&#39;d: C, 57.48; H, 4.54. Found: C, 57.51; H, 4.59. 
     The two diasteriomers (α- and β-) are separated by high performance liquid chromatography. 
     EXAMPLE 3 
     Preparation of 6,7-dichloro-2,3-dihydro-5-(5-methyl-32 -cyclohexen-1-yl)-2-benzofurancarboxylic acid 
     Step A: 5,6-Dichloro-2,3-dihydro-5-(1-oxo-2-butenyl)-2-benzofurancarboxylic acid 
     To a stirred solution of ethyl 6,7-dichloro-2,3-dihydro-2-benzofurancarboxylate (13.4 g, 0.05 mole) and crotonyl chloride (8.15 g, 0.09 mole) in CH 2  Cl 2  (30 ml) cooled to 5° C. in an ice bath is added aluminum chloride (22.5 g, 0.17 mole) over a 10 minute period. The reaction mixture is stirred for 1  hour at 25° C. then for 20 minutes at reflux. The reaction mixture is poured into ice water, extracted into ether, washed with water and the ether evaporated in vacuo. The residue is treated with 10 N sodium hydroxide (100 ml) and the resultant sodium salt filtered and suspended in dilute hydrochloric acid which is extracted with ether (206 ml), washed with water, dried over magnesium sulfate, evaporated to 50 ml and treated with hexane to give 6,7-dichloro-2,3-dihydro-5-(1-oxo-2-butenyl)-2-benzofurancarboxylic acid. 
     Step B: 6,7-Dichloro-2,3-dihydro-5-(5-methyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid 
     To a stirred refluxing solution of ethyl acetoacetate (2.9 g, 0.022 mole) and sodium methoxide (1.2 g, 0.022 mole) in ethanol (50 ml) is added 6,7-dichloro-2,3-dihydro-5-(1-oxo-2-butenyl)-2-benzofurancarboxylic acid (3.0 g, 0.01 mole). Refluxing is continued for 3 hours, the ethanol is distilled in vacuo and the residue is treated with ether and diluted hydrochloric acid. The ether is washed with water, dried over magnesium sulfate, and evaporated in vacuo. Trituration of the residue with butyl chloride gives 6,7-dichloro-2,3-dihydro-5-(5-methyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid. 
     EXAMPLE 4 
     Preparation of 1-carboxy-1-methylethyl 6,7-dichloro-2,3-dihydro-5-(5-methyl-3-oxo-2-cylcohexen-1-yl)-2- benzofurancarboxylate 
     To a stirred solution of 6,7-dichloro-2,3-dihydro-5-(5-methyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylate (2.06 g, 0.006 mole) in tetrahydrofuran (50 ml) is added 1,1&#39; -carbonyldiimidazole (0.97 g, 0.006 mole). The solution is stirred for 1 hour and then 2-hydroxy-2-methylpropionic acid (0.62 g, 0.006 mole) in tetrahydrofuran (25 ml) is added and stirring is continued overnight. The tetrahydrofuran is evaporated in vacuo and the residue chromatographed on silica (300 g), eluting with CH 2  Cl 2  /tetrahydrofuran/acetic acid (100/2/1). Evaporation of the pertinent fractions gives 1-carboxy-1-methylethyl 6,7-dichloro 2,3-dihydro-5-(5-methyl-3-oxo-2-cylcohexen-1-yl )-2-benzofurancarboxylate. 
     EXAMPLE 5 
     Parenteral Solution of 6,7-dichloro-2,3-dihydro-5(6-ethyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid 
     6,7-Dichloro-2,3-dihydro-5-(6-ethyl-3-oxo-2cyclohexen-1-yl)-2-benzofurancarboxylic acid (500 mg) is dissolved by stirring and warming with 0.25 N sodium bicarbonate solution (5.4 ml). The solution is diluted to 10 ml and sterilized by filtration. All the water that is used in the preparation is pyrogen-free. The concentration of the active agent in the final solution is 5%. 
     Similar parenteral solutions can be prepared by replacing the active ingredient of this Example by any of the other compounds of this invention. 
     EXAMPLE 6 
     Dry-Filled Capsules Containing 100 mg of Active Ingredient Per Capsule 
     
         ______________________________________              Per Capsule______________________________________6,7-Dichloro-2,3-dihydro-5-                100 mg(6-ethyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acidLactose               99 mgMagnesium Stearate    1 mgCapsule (Size No. 1) 200 mg______________________________________ 
    
     6,7-Dichloro-2,3-dihydro-5-(6-ethyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid is reduced to a No. 60 powder and then the lactose and magnesium stearate are passed through a No. 60 bolting cloth onto the powder and the combined ingredients admixed for 10 minutes and then filled into a No. 1 dry gelatin capsule. 
     Similar capsules can be prepared by replacing the active ingredient of this Example by any of the other compounds of this invention. 
     EXAMPLE 7 
     Parenteral Solution of 6,7-dichloro-2,3-dihydro-5(5-methyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylic acid 
     6,7-Dichloro-2,3-dihydro-5-(5-methyl-3-oxo-2- cyclohexen-1-yl)-2-benzofurancarboxylic acid (500 mg) is dissolved by stirring and warming with 0.25 N sodium bicarbonate solution (5.4 ml). The solution is diluted to 10 ml and sterilized by filtration. All the water that is used in the preparation is pyrogen-free. The concentration of the active agent in the final solution is 5%. 
     Similar parenteral solutions can be prepared by replacing the active ingredient of this Example by any of the other compounds of this invention. 
     EXAMPLE 8 
     Dry-Filled Capsules Containing 100 mg of Active Ingredient Per Capsule 
     
         ______________________________________             Per Capsule______________________________________1-carboxy-1-methylethyl-               100 mg6,7-dichloro-2,3-dihydro-5-(5-methyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylateLactose              99 mgMagnesium Stearate   1 mgCapsule (Size No. 1)               200 mg______________________________________ 
    
     1-Carboxy-1-methylethyl 6,7-dichloro-2,3-dihydro-5-(5-methyl-3-oxo-2-cyclohexen-1-yl)-2-benzofurancarboxylate is reduced to a No. 60 powder and then the lactose and magnesium stearate are passed through a No. 60 bolting cloth onto the powder and the combined ingredients admixed for 10 minutes and then filled into a No. 1 dry gelatin capsule. 
     Similar capsules can be prepared by replacing the active ingredient of this Example by any of the other compounds of this invention.