according to the present invention the asymmetric diesters of general formula ( i ) may be prepared by reacting the pure ( r )- enantiomer of acids of formula ( ii ) with a compound of formula ( iii ). the reaction may be performed in the presence of a coupling agent ( e . g . : dicyclohexylcarbodiimide , n , n &# 39 ;- carbonyldiimidazole or diethyl cyanophosphonate ) optionally in the presence of a promoting agent ( e . g . : n - hydroxysuccinimide or 4 - dimethylaminopyridine ) in aprotic or chlorinated solvents ( e . g . : n , n - dimetylformamide or chloroform ) at temperatures ranging from - 10 ° to 140 ° c . according to well known synthetic methods : albertson , org . react . 12 , 205 - 218 ( 1962 ); doherty et al ., j . med . chem . 35 , 2 ( 1992 ); staab et al ., newer methods prep . org . chem . 5 , 61 ( 1968 ); ishihara , chem . pharm . bull . 39 , 3236 ( 1991 ). alternatively , the compounds of formula ( i ) may be prepared by first reacting the ( r )- enantiomer of the above acid intermediates ( ii ) with alkyl chloroformate in presence of a tertiary amine ( e . g . triethylamine ), then adding the intermediate ( iii ) at 0 °- 80 ° c . optionally , a promoting agent ( e . g ., 1 - hydroxypiperidine ) may be added before the intermediate ( iii ) addition , see albertson , org . react . 12 , 157 ( 1962 ). the compounds of the invention may also be prepared by conversion of the ( r )- enantiomer of the acid intermediates ( ii ) into the corresponding acyl halide using inorganic acid halides ( e . g ., phosphorous pentachioride or thionyl chloride ) in a chlorinated solvent ( e . g ., chloroform , dichloroethane , dichloromethane or 1 , 1 , 1 - trichloroethane ), optionally in the presence of promoting agents ( e . g ., n , n - dimethylformamide ) at temperatures ranging between - 10 ° and 65 ° c . said acyl halides may or may not be isolated before the addition of the intermediate ( iii ). the homo - chiral ( s )- enantiomers of diesters of general formula ( i ) so obtained , may be purified according to methods known in the art , either as base ( e . g . : by column chromatography ) or as salts ( e . g . : by re - precipitation or recrystallization ). the pharmaceutically acceptable salts of the chiral diesters may be prepared from the free bases in conventional manner . preferred pharmaceutically acceptable acid addition salts are those of hydrochloric , sulfuric , maleic , succinic , citric , methanesulfonic and toluenesulfonic acids without limitation . the compounds of the present invention , the s - enantiomers , may be administered orally , parenterally or rectally in pharmaceutical preparations which comprise the active compound in combination with pharmaceutically acceptable carriers . carriers can be solid , semisolid or liquid diluents as well as capsules and may optionally provide modified release of the active drug . the selection of the most suitable carriers will depend on the administration route . for example , a preparation to be administered orally , in form of tablets , can include , in addition to the active substance , solubilizers ( e . g . : a polyethoxylated fatty acid ), components which modify the drug release ( e . g . : hydroxypropylmethyl cellulose ), fillers ( e . g . : lactose ), binders ( e . g . : hydroxypropylmethyl cellulose ) and / or lubricants ( e . g . : sodium stearylfumarate ). the tablets can be coated with suspensions of coloring pigments ( e . g . : iron oxide ) and film forming agents ( e . g . : cellulose derivative ). aqueous solutions of the drug for parenteral use can include co - solvents ( e . g . : polyethylene glycol ). usually the amount of the active compound ranges between 0 . 1 and 99 % by weight of the total formulation , preferably between 0 . 5 and 20 % by weight in formulations for injection and between 2 and 50 % by weight in formulations for oral administration : an effective amount of a compound having formula i , for increasing contractility of the head muscle is an amount of the compound which is effective to lower the diastolic blood pressure about 20 % to about 30 %. the daily dose of the active compound depends on individual needs ( e . g . : the patient &# 39 ; s condition , body weight , age or sex etc .) as well as on the administration route . generally , the oral dosage may range from 0 . 1 to about 100 mg , preferably from about 1 to about 20 mg , of active compound per mammal ( including human ) per day . the s - enantiomers of the present invention were tested in vivo in a dog model , in comparison with the corresponding racemates at different doses in order to assess their pharmacological activity . percent changes on diastolic blood pressure ( dbp ) and the cardiac contractility were detected . the results show the high vascular selectivity of the s - enantiomers and the positive inotropic effect on the head contractility . both the effects indicate a potential use of these compounds as therapeutic agents for the treatment of head failure . to further illustrate the present invention and the advantages thereof , the following specific examples are given , it has to be understood that they are intended only as illustrative and not limitative . thionyl chloride 0 . 13 ml was added , at - 10 ° c ., to a stirred suspension of 0 . 54 g of ( r )-(-)- 1 , 4 - dihydro - 2 , 6 - dimethyl - 4 -( 3 - nitrophenyl )- 5 - methoxycarbonylpyridine - 3 - carboxylic acid ( prepared as described in a . ashimori et al ., chem . pharm . bull . 39 ., 108 - 111 , ( 1991 )) in 2 . 9 ml of anhydrous dichloromethane and 0 . 75 ml of anhydrous n , n - dimethylformamide kept under nitrogen atmosphere and sheltered from the direct light . after 1 h at 0 ° c ., a solution of 0 . 48 g of 2 , n - dimethyl - n -( 3 , 3 - diphenylpropyl )- 1 - amino - 2 - propanol , ( prepared as described in u . s . pat . no . 4 , 772 , 621 ), in 1 ml of dichloromethane was added at - 5 ° c . after stirring for 3 hours at 0 ° c . and standing overnight at 20 °- 25 ° c ., the solvent was evaporated in vacuo and the residue was dissolved in 20 ml of ethyl acetate . the organic phase was washed sequentially with brine ( 4 ml ), 10 % aqueous sodium carbonate solution ( 5 × 4 ml ), brine ( 4 ml ), 1n hydrochloric acid ( 5 × 5 ml ), brine ( 4 ml ), 10 % aqueous sodium carbonate solution ( 2 × 5 ml ) and finally with brine ( 4 ml ). the organic phase was dried over anhydrous sodium sulfate and evaporated to dryness in vacuo . the residue was purified by flash chromatography on silica gel column eluting with petroleum ether - acetone 85 : 15 . the unitary tlc fractions ( petroleum ether -- acetone 7 : 3 by volume and chloroform -- 5n methanolic ammonia 99 : 21 . 1 by volume ) were evaporated to give a residue that was dissolved in 75 ml of diethyl ether containing 3 % of acetone . after filtration the solution was acidified with 3n ethereal hydrogen chloride and the precipitate was collected by suction and dried at 78 ° c ./ 15 mmhg to give 0 . 66 g of the title compound . m . p . 115 °- 125 ° c . ; α ! d 25 =+ 70 . 56 ° ( meoh , c = 0 . 981 ). elemental analysis % for c 36 h 41 n 3 o 6 . hcl . 0 . 5 h 2 o : found : c , 65 . 47 ; h , 6 . 57 ; n , 6 . 29 ; cl , 5 . 32 ; h 2 o , 1 . 68 . calcd . : c , 65 . 79 ; h , 6 . 60 ; n , 6 . 39 ; cl , 5 . 39 ; h 2 o , 1 . 37 . 1 h - nmr spectrum of the base at 200 mhz ( cdcl 3 , ( δ )): ______________________________________8 . 10 ( m , 1h ) nitrophenyl , ch in 27 . 97 ( m , 1h ) nitrophenyl , ch in 47 , 62 ( m , 1h ) nitrophenyl , ch in 67 . 33 ( dd , 1h ) nitrophenyl , ch in 57 . 29 - 7 . 10 ( m , 10h ) h aromatics of benzhydryl5 . 79 ( bs , 1h ) pyridine , nh5 . 05 ( s , 1h ) pyridine , ch in 43 . 92 ( t , 1h ) benzhydryl ch3 . 63 ( s , 3h ) cooch . sub . 32 . 57 ( m , 2h ) oc ( ch . sub . 3 ). sub . 2 ch . sub . 2 n2 . 40 - 2 . 23 ( m , 2h ) n ( ch . sub . 3 ) ch . sub . 2 ch . sub . 22 . 33 / 2 . 27 ( 2s , 6h ) pyridine , ch . sub . 3 in pos . 2 and 62 . 19 - 2 . 09 ( m , 2h ) n ( ch . sub . 3 ) ch . sub . 2 ch . sub . 22 . 17 ( s , 3h ) nch . sub . 31 . 35 / 1 . 31 ( 2s , 6h ) oc ( ch . sub . 3 ). sub . 2 ch . sub . 2 n______________________________________ a mixture comprising n - methyl - 3 , 3 - diphenylpropylamine hydrochloride ( 2 . 61 g ) ( prepared as described in de 935 , 468 ), acetic anhydride ( 1 ml ) and formaldehyde ( 37 % in water ; 0 . 9 ml ), was refluxed for 30 minutes . then a solution of isobutyraldheyde ( 1 ml ) in acetic anhydride ( 1 ml ) was added dropwise and the mixture was maintained at reflux temperature for further 30 minutes . the solvent was then evaporated under vacuum and the residue dissolved in water , alkalinized and extracted with diethyl ether . the organic layer , was separated , dried and , after evaporation of the solvent , the residue was purified by silica - gel chromatography eluting with methylene chloride / methanol ( 98 : 2 to 96 : 4 ). pure fractions were collected and the solvent was evaporated to give the mannich base n -( 3 , 3 - diphenylpropyl )- n , 2 , 2 - trimethyl - 3 - aminopropanaldehyde ( compound a ) ( 1 . 55 g ), which was characterized by nmr spectrometry . ______________________________________9 . 5 ( s , 1h ) cho7 . 3 ( s , 10h ) aromatics4 . 0 ( t , 1h ) ph . sub . 2 -- ch2 . 7 - 1 . 9 ( m , 9h ) 3 ch . sub . 2 and nch . sub . 31 . 0 ( s , 6h ) c ( ch . sub . 3 ). sub . 2______________________________________ sodium borohydride ( 0 . 25 g ) was added at 0 / 3 ° c . to a solution of 1 . 5 g of compound a ) in methanol ( 7 ml ) cooled at 0 / 3 ° c . for 30 minutes , and then at room temperature for 1 hour . the resulting solution was poured in 35 ml of water , the crude was extracted with diethyl ether and the organic layer was separated and extracted with a solution of oxalic acid ( 0 . 6 g in 35 ml of water ). the aqueous acidic solution , washed twice with diethyl ether , made alkaline with 30 % sodium hydroxide ( 1 ml ) was then extracted with diethyl ether . to the ethereal solution , after drying over sodium sulphate , was added hcl in diethyl ether and the crude hydrochloride was collected by filtration and crystallized from acetone to give 1 . 26 g of the title product melting at 147 °- 148 ° c . ______________________________________10 . 8 - 9 . 9 ( m , 1h ) nh . sup .+ 7 . 7 - 7 . 2 ( m , 10h ) aromatics5 . 0 - 4 . 4 ( m , 1h ) oh4 . 1 ( t , 1h ) ph . sub . 2 -- ch3 . 7 ( s , 2h ) ch . sub . 2 o3 . 5 - 2 . 5 ( m , 9h ) 3 ch . sub . 2 and nch . sub . 31 . 1 ( s , 6h ) c ( ch . sub . 3 ). sub . 2______________________________________ the title compound was prepared according to the method described in example 1 , using 2 , 2 , n - trimethyl - n -( 3 , 3 - diphenylpropyl )- 1 - amino - 3 - propanol , prepared as described in example 2 , instead of 2 , n - dimethyl - n -( 3 , 3 - diphenylpropyl )- 1 - amino - 2 - propanol . the crude product was purified by flash chromatography on silica gel column eluting with n - hexane - ethyl acetate gradient from 70 : 30 to 65 : 35 . the fractions containing the pure base were pooled , the solvents were evaporated in vacuo to dryness , and the residue was dissolved in diethyl ether . after filtration the solution was acidified with 3 n ethereal hydrogen chloride and the precipitate was collected by vacuum filtration and dried at 78 ° c ./ 15 mmhg to give the title compound , m . p . 116 °- 127 ° c . 1 h - nmr spectrum at 200 mhz ( cdcl 3 , ( δ )): ______________________________________11 . 20 - 11 . 55 ( bs , 1h ) nh . sup .+ 8 . 06 ( dd , 1h ) nitrophenyl , ch in 27 . 90 - 8 . 03 ( m , 1h ) nitrophenyl , ch in 47 . 60 - 7 . 45 ( dd , 1h ) nitrophenyl , ch in 67 . 10 - 7 . 45 ( m , 11h ) nitrophenyl , ch in 5 and benzhydryl aromatic h &# 39 ; s6 . 68 - 6 . 82 ( d , 1h ) pyridine , nh5 . 07 ( d , 1h ) pyridine , ch in 43 . 85 - 4 . 15 ( m , 3h ) benzhydryl ch and cooch . sub . 23 . 67 ( s , 3h ) cooch . sub . 32 . 50 - 3 . 15 ( m , 9h ) ch . sub . 2 n ( ch . sub . 3 ) ch . sub . 2 ch . sub . 2 ch2 . 34 / 2 . 41 ( 2d , 6h ) pyridine , ch . sub . 3 in pos . 2 and 61 . 70 ( bs , 1 . 4h ) h . sub . 2 o0 . 98 / 1 . 18 ( 2d , 6h ) ch . sub . 2 c ( ch . sub . 3 ) ch . sub . 2______________________________________ the ( s )- enantiomers prepared in examples 1 and 3 were tested for their in vivo pharmacological activity in a dog model , and compared to the racemate of compound of example 1 . male beagle dogs weighing 11 - 13 kg , 12 months old , from green - hill and morini allevamenti ( italy ), were used . all dogs were anaesthetized with sodium pentobarbital ( 30 mg / kg i . v . for induction and 2 mg / kg / hour i . v . for maintenance ), and artificially ventilated with a pump via a cuffed endotracheal tube . intraventricular and arterial blood pressure were monitored by means of a millar mikro - tip catheter with two pressor sensors inserted in the left ventricle via left common carotid artery . the right femoral vein was cannulated to allow drug infusion . the following parameters were evaluated : systolic ( sbp ), diastolic ( dbp ) and mean ( mbp ) blood pressure , left ventricular systolic pressure ( lvp ) and first derivative of lvp , dp / dt max as an index of cardiac contractility . the compounds were tested at the following dosages ( intravenously administered in cumulative manner ): ______________________________________compound dose ( μg / kg ) ______________________________________racemate corresponding to example 1 3 , 10 , 30example 1 0 . 5 , 1 , 3 , 5example 3 1 , 3 , 5 , 10______________________________________ the results are reported in fig1 - 3 . the percent changes on diastolic blood pressure ( dbp ) and cardiac contractility , at the different doses tested , are shown . in particular , fig1 and 3 show the effects exerted on the hemodynamics parameters in the dog by : the racemate corresponding to example 1 , the ( s )- enantiomer of example 1 and the ( s )- enantiomer of example 3 respectively . fig1 clearly shows that the racemate corresponding to the compound of example 1 has a potent blood pressure lowering effect ( dbp ) accompanied by a slight reduction of cardiac contractility ( dp / dt max ). in contrast , fig2 and 3 show that the noticeable blood pressure lowering effects of compounds of examples 1 and 3 are associated with an increase of dp / dt max . the increase in the dp / dt max illustrates the positive inotropic effect . the invention has been described above by reference to preferred embodiments but , as those skilled in the art will appreciate , many additions , omissions and modifications are possible all within the scope of the claims below . all patents and literature references cited in this specification are hereby incorporated by reference in their entirety . in case of inconsistencies , the present description , including the definitions and interpretations , will prevail .
the present invention provides s - enantiomers of 1 , 4 - dihydropyridines useful for the treatment of heart failure , preparation of compositions thereof and a method for the treatment of hypertension and heart failure comprising administration of these compounds .