Patent Application: US-84218192-A

Abstract:
compounds of formula , wherein r 1 is selected from the group consisting of an alkyl group , an aralkyl group , an alkenyl group , a cycloalkyl group , in which the alkyl , aralkyl , alkenyl or cycloalkyl group is unsubstituted or substituted with one or more substituents selected from the group consisting of a halogen atom , e . g . cl or br , a hydroxyl group or a straight or branched - chain alkoxy group containing from 1 to 6 carbon atoms ; and the pharmaceutically acceptable acid addition salts thereof . such compounds are prodrugs of trh and are characterized by having a higher lipophilicity than trh and possessing a high resistance toward degradation by trh - inactivating enzymes . such compounds will after administration be converted into trh .

Description:
as examples of the compounds of formula i may be mentioned compounds in which r 1 is one of the following groups : methyl , ethyl , propyl , isopropyl , butyl , sec . butyl , pentyl , hexyl , heptyl , octyl , nonyl , decyl , pentadecyl , t .- butyl , allyl , 8 - hydroxyoctyl , 2 - chloroethyl , 8 - isopropoxyoctyl , benzyl , phenethyl , 2 - butenyl , cyclohexyl or cyclopentyl . the prodrug compounds of formula i of the present invention can be used to treat any condition for which the parent trh is useful . the compounds may be administered orally , topically , parenterally , rectally , buccally , or by inhalation spray in dosage forms or formulations containing conventional , non - toxic pharmaceutically acceptable carriers , adjuvants or vehicles . the preferred route of administration is by parenteral injection . the compounds of the present invention may be prepared by various methods . one method comprises reacting trh with a compound of the formula ii ## str4 ## wherein r 1 is as defined above and x is a leaving group . as examples of leaving groups x may be mentioned chlorine , bromine , iodine , fluorine , and 4 - nitrophenyloxy . a preferred leaving group is chlorine . the reaction is conveniently carried out in a solvent such as dioxane , acetone , acetonitrile , n , n - dimethylformamide , tetrahydrofuran , pyridine or the like , or in water or mixtures of water - aprotic solvents , at a temperature of from - 10 ° c . to 80 ° c ., for from 1 / 2 to 72 h . the reaction is preferably conducted in the presence of a base such as an alkali metal carbonate or an organic base such as triethylamine or pyridine . several compounds of formula ii in which x is chlorine and methods for preparing them are known from the literature , see e . g . matzner et al . ( 1964 ). another method for preparing the compounds of the present invention comprises reacting trh with an alkoxyformic anhydride of the formula iii wherein r 1 is as defined above . the reaction is conveniently carried out in water or mixtures of water - aprotic solvents . to form acid addition salts of the compounds of formula i said compounds are treated with suitable pharmaceutically acceptable inorganic or organic acids by standard procedures . the present invention is further illustrated by the following examples which , however , are not construed to be limiting . chromatographical data of the prepared compounds are given in table 1 . as indicated above reaction of trh with chloroformates may result in either n ( 1 )- or n ( 3 )- substitution at the imidazole group . however , the compounds described in the following examples consisted predominantly (& gt ; 90 %) or entirely of a single product as determined on basis of hplc analysis and kinetic experiments . the products are believed to be n ( 3 )- substituted derivatives . to a solution of trh ( 3 mmol , 1 . 09 g ) in 10 ml of n , n - dimethylformamide was added 3 . 6 mmol ( 0 . 51 ml ) of triethylamine followed by 3 . 6 mmol ( 0 . 72 ml ) of n - octyl chloroformate . the mixture was stirred at room temperature for 2 . 5 h , poured into 60 ml of water and then extracted with ethyl acetate ( 2 × 75 ml ). the combined ethyl acetate extracts were washed with water ( 2 × 50 ml ), dried over anhydrous sodium sulphate and evaporated in vacuo . the residue obtained was recrystallized from ethyl acetate - ether - petroleum ether to give the title compound in a yield of 70 %. mp . 79 °- 82 ° c . anal . : calc . for c 25 h 38 n 6 o 6 , 1h 2 o : c , 55 . 96 ; h , 7 . 51 ; n , 15 . 66 . found : c , 56 . 07 ; h , 7 . 69 ; n , 15 . 44 . the compound obtained as described in example 1 was dissolved in ethyl acetate ( 2 ml ) and 0 . 25 ml of a 2 . 5m methanolic hcl solution was added . by subsequent addition of ether and petroleum ether the title compound precipitated . after standing at - 20 ° c . for 4 h the precipitate was filtered off , washed with ether and dried in vacuo over phosphorous pentoxide . yield : 85 %. to a mixture of trh ( 1 mmol , 362 mg ) in 20 ml of acetonitrile was added 1 . 2 mmol of triethylamine followed by 1 . 2 mmol of n - hexyl chloroformate . the mixture was stirred at room temperature for 5 h and evaporated under reduced pressure . the residue obtained was taken up in water ( 10 ml ) and ethyl acetate ( 20 ml ). the organic phase was separated and the aqueous phase reextracted with 20 ml of ethyl acetate . the combined extracts were washed with a 2 % sodium bicarbonate solution followed by water , dried over anhydrous sodium sulphate and evaporated under reduced pressure . the residue obtained was recrystallized from ethanol - ether - petroleum ether and finally dried in vacuo over phosphorous pentoxide to give the title compound in a yield of 67 %. mp . 71 °- 73 ° c . anal . : calc . for c 23 h 34 n 6 o 6 , 1h 2 o : c , 54 . 32 ; h , 7 . 14 ; n , 16 . 52 . found : c , 54 . 20 ; h , 7 . 25 ; n , 16 . 40 . by following the procedures of example 1 and 3 and using the appropriate , chloroformate several more n - alkoxycarbonyl derivatives of trh accodring to this invention are obtained . the structure and properties of these derivatives are shown in table 1 . the lipophilicity of the derivatives of the present invention and of trh was assessed by measuring the apparent partition coefficients ( p ) of the compounds between 1 - octanol and 0 . 02m phosphate buffer of ph 7 . 4 . the log p values obtained are shown in table 1 . the results obtained show clearly that it is readily feasible to obtain prodrug derivatives possessing a much higher lipophilicity than the parent trh . it is also apparent that by selecting an appropriate r 1 - substituent of the compounds of formula i it is readily possible to obtain prodrug derivatives with varying and any desirable lipophilicity . the chromatographic capacity factor obtained by reversed - phase column chromatography is also a commonly used measure for the relative lipophilicities of various compounds . the capacity factor k &# 39 ; of a solute is defined as : where t r is the retention time of the solute and t 0 is the elution time of the solvent . with a mobile phase system consisting of methanol - 0 . 1 % phosphoric acid ( 1 : 20 v / v ) containing 10 - 3 m triethylamine and using a nova - pak cn hp radial pak reversed - phase column ( 8 × 100 mm )( waters ass .) the various derivatives showed the k &# 39 ; values given in table 1 . these data also illustrate the increased lipophilicity of the n - alkoxycarbonyl derivatives relative to the parent trh . solutions of various compounds of formula i in aqueous buffer solutions or 80 % human plasma solutions as well as in a buffer solution ( ph 7 . 4 ) containing pyroglutamyl aminopeptidase ( a calf liver preparation obtained from boehringer , mannheim , f . r . g .) were kept at 37 ° c . the initial concentration of the derivatives was in the range 10 - 5 - 10 - 3 m . at various times an aliquot of the solutions was withdrawn and analyzed by hplc for remaining ( intact ) derivative as well as for trh . for the plasma solutions the aliquot ( 250 μl ) withdrawn was added to 500 μl of a 2 % solution of zinc sulphate in methanol - water ( 1 : 1 v / v ) in order to deproteinize the plasma . after mixing and centrifugation for 3 min at 13 , 000 rpm , 20 μl of the clear supernatant was analyzed by hplc as described above . the reaction conditions used for the studies with the pyroglutamyl aminopeptidase enzyme were identical to those previously described by bundgaard & amp ; moss ( 1989 ). an hplc method was used for the determination of trh and its derivatives . in this method a reversed - phase column described above was eluted at ambient temperature with mobile phase systems consisting of 10 - 50 % v / v acetonitrile in 0 . 1 % phosphoric acid with triethylamine added in a concentration of 10 - 3 m , the concentration of acetonitrile being adjusted for each compound to give an appropriate retention time ( 3 - 8 min ). for the determination of trh formed upon hydrolysis of the various derivatives a mobile phase system consisting of acetonitrile - 0 . 1 % phosphoric acid ( 1 : 20 v / v ) containing 10m triethylamine was used . the flow rate was 1 . 5 ml min and the column effluent was monitored at 215 nm . quantitation of the compounds was done by measuring the peak heights in relation to those of standards chromatographed under the same conditions . the cleavage of the derivatives displayed strict first - order kinetics in all reaction solutions . pseudo - first - order rate constants and hence the half - lives of degradation of the derivatives were calculated from the slopes of linear plots of the logarithm of remaining derivative against time . the compounds were hydrolyzed quantitatively to trh in aqueous solution in the ph - range 0 . 3 - 10 as shown by the example in fig1 . they showed maximal stability at ph 5 - 6 , cf . fig2 . the time for 10 % degradation of n - octyloxycarbonyl trh in aqueous solution at ph 5 . 8 and 20 ° c . was found to be 76 h . at ph 7 . 4 and 37 ° c . the half - lives of hydrolysis ranged from 9 to 37 h ( table 2 ). in the presence of pyroglutamyl aminopeptidase ( papase i ) trh is rapidly degraded . under conditions where trh showed a half - life of degradation of 4 min the various n - alkoxycarbonyl derivatives proved more stable as seen from the data in table 2 . in the presence of human plasma the n - alkoxycarbonyl derivatives showed a markedly higher stability than trh . as seen from table 2 the half - lives of degradation ranged from 0 . 5 to 6 . 6 h , whereas trh degraded with a half - life of 9 min . for the consideration of the derivatives as prodrugs of trh a crucial point is evidently their degradation pathways . ideally , the compounds should be hydrolyzed in plasma at the imidazole - protected moiety , releasing trh in quantitative amounts . surprisingly , this was indeed found to be the case for the derivatives . the reactions taking place in plasma can be illustrated as shown in scheme 1 . by virtue of spontaneous as well as plasma enzyme - catalyzed hydrolysis the n - alkoxycarbonyl derivatives are exclusively hydrolyzed at the imidazole carbamate moiety to yield trh which subsequently degrades to yield pyroglutamic acid and l - histidyl - l - prolineamide due to the trh - specific pyroglutamyl aminopeptidase enzyme ( papase ii ) present in plasma . the latter process ( i . e ., degradation of trh ) showed a first - order half - life of 9 min at low trh concentrations ( less than about 2 × 10 - 5 m ) in 80 % human plasma and 37 ° c . whereas the degradation of trh was found to follow zero - order kinetics at higher concentrations . in 80 % human plasma and at 37 ° c . a zero - order rate constant of 7 . 2 × 10 - 7 m min - 1 was determined for trh at initial concentrations of 10 - 4 - 10 - 3 m . ## str5 ## the quantitative conversion of the n - alkoxycarbonyl derivatives to trh in 80 % human plasma solutions at 37 ° c . was demonstrated by analyzing the reaction solutions for trh using the hplc procedure described above . the data obtained for some derivatives are shown in fig3 and 4 . as can be seen , trh is formed from the derivatives in human plasma solutions . the apparent greater amounts of trh occurring in solutions with the highest initial concentration of the derivatives is due to the fact that at the concentrations used trh is inactivated according to zero - order kinetics , implying that the inactivation rate in terms of percentage of degradation per unit of time decreases with increasing concentration . the time - courses for trh such as those shown in fig3 and 4 were subjected to kinetic analysis for a consecutive reaction scheme and this showed clearly that trh is formed in stoichiometric amounts (& gt ; 90 %) at any varying initial derivative concentration . these experiments demonstrate that the n - alkoxycarbonyl derivatives in fact are prodrug derivatives of trh in that the parent active compound is released at conditions similar to those prevailing in vivo . it is also apparent that by appropriate variation of the r 1 - substituent of the compounds of formula i it is readily possible to vary the rate of hydrolysis and hence to control and modify the rate of trh production . thus , more slowly hydrolyzing derivatives may function as a trh depot , protecting the derivatized trh against rapid enzymatic degradation in the blood . table 1______________________________________partition coefficients ( p ) and chromatographic capacity factors ( k &# 39 ;) of trh and various trh derivativescompound log p . sup . a log k &# 39 ; ______________________________________trh - 2 . 46 & lt ; 0 . 4r . sub . 1 in formula l : ch . sub . 3 1 . 88 0 . 71c . sub . 2 h . sub . 5 - 1 . 30 0 . 85ch ( ch . sub . 3 ). sub . 2 - 0 . 80 0 . 96n - c . sub . 4 h . sub . 9 - 0 . 47 1 . 07ch . sub . 2 ch ( ch . sub . 3 ). sub . 2 - 0 . 44 1 . 09n - c . sub . 6 h . sub . 13 0 . 71 1 . 29n - c . sub . 8 h . sub . 17 1 . 88 1 . 50ch . sub . 2 c . sub . 6 h . sub . 5 - 0 . 11 -- c . sub . 6 h . sub . 10 ( cyclohexyl ) 0 . 60 1 . 28ch . sub . 2 ch . sub . 2 cl - 1 . 10 -- ch ( c . sub . 2 h . sub . 5 ). sub . 2 0 . 20 -- ch ( c . sub . 3 h . sub . 7 ). sub . 2 1 . 20 -- ch . sub . 2 ch ( c . sub . 2 h . sub . 5 ) c . sub . 4 h . sub . 9 1 . 82 -- ______________________________________ . sup . a between octanol and 0 . 02 m phosphate buffer ph 7 . 4 ( 21 ° c .) table 2______________________________________data on the rate of hydrolysis of trhand its various n - alkoxycarbonyl derivatives half - lives at 37 ° c . ph 7 . 4 pyroglutamyl 80 % v / v humancompound buffer aminopeptidase . sup . a plasma______________________________________trh -- 4 min 9 minr . sub . 1 in formula l : ch . sub . 3 9 . 3 h 12 min 2 . 8 hc . sub . 2 h . sub . 5 14 . 2 h 23 min 3 . 8 hch ( ch . sub . 3 ). sub . 2 35 . 8 h 29 min 6 . 6 hn - c . sub . 4 h . sub . 9 19 . 0 h 11 min 4 . 3 hch . sub . 2 ch ( ch . sub . 3 ). sub . 2 19 . 0 h 11 min 4 . 3 hn - c . sub . 6 h . sub . 13 17 . 9 h 8 min 1 . 2 hn - c . sub . 8 h . sub . 17 17 . 5 h 24 min 0 . 5 hch . sub . 2 c . sub . 6 h . sub . 5 9 . 0 h 7 min - 1 . 6hc . sub . 6 h . sub . 10 ( cyclohexyl ) 36 . 8 h 22 min 6 . 4 h______________________________________ . sup . a these data are halflives for the degradation in buffer solution ( p 7 . 4 ) containing pyroglutamyl aminopeptidase ( 0 . 01 unit / ml ). the feasibility of achieving transdermal delivery of trh via the prodrugs ot the present invention was evaluated by diffusion experiments in vitro using human skin samples . whole abdominal human skin obtained under autopsy was used . the skin was stored at - 18 ° c . and was allowed to thaw gradually at room temperature before use . all subcutaneous fat was removed and the skin cut into pieces . the excised skin was mounted in open franz diffusion cells ; they had an available diffusion area of 0 . 70 cm 2 . the dermal side of the skin was exposed to the receptor medium ( 5 ml of 0 . 05m isotonic phosphate buffer solution of ph 7 . 2 ) which was stirred magnetically and kept at a constant temperature of 37 ° c . with a circulating water bath . the compounds were applied as 5 % w / v solutions in 0 . 05m phosphate buffer ( final ph being 6 . 0 ) or propylene glycol ( 100 or 200 μl ). at appropriate intervals samples of 1 ml were removed from the receptor phase and replaced with fresh buffer . the samples were immediately analyzed for trh and prodrug content by hplc as described above . the permeation studies of each compound in each vehicle were done in triplicate . in the case of trh , no measurable amounts of the compound could be detected in the receptor phase during diffusion experiments lasting up to 200 h . the limit of detection of trh was about 0 . 5 μg ml - 1 . in contrast , the more lipophilic n - octyloxycarbonyl trh derivative readily penetrated human skin . by applying this prodrug in an aqueous solution ( ph 6 . 0 ) at a concentration of 5 %, a steady - state flux of 0 . 044 ± 0 . 006 μmol trh / h / cm 2 , corresponding to 16 μg trh / h / cm 2 , was observed . essentially all of the prodrug applied was converted to the parent trh during diffusion through the human skin samples . using propylene glycol as a vehicle and a prodrug concentration of 5 %, a flux of 3 . 6 μg / h / cm 2 was obtained . the good skin penetration of the octyloxycarbonyl prodrug derivative can most likely be attributed to its combination of high water and lipid solubility . the feasibility of transdermal delivery for trh via the prodrug approach of the present invention can be assessed by comparing the daily doses of trh usually used via parenteral administration with those obtainable by transdermal delivery . it the area of the patch for transdermal delivery is 20 cm 2 and if a flux of 16 μg / h / cm 2 is used it can readily be calculated that it is possible to deliver 320 μg trh / h or 7 . 6 mg over 24 h . this amount is in the same range ( 0 . 5 - 5 mg ) as that often given of trh by infusion or injection during 24 h . banks , w . a . & amp ; 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