it has now been found that the 1 , 4 - dihydropyridines described in more detail below are outstandingly capable of increasing the activity of cytostatics against tumour cells ( synergism ) and of overcoming the resistance of tumour cells to certain cytostatics . surprisingly , it has also been found that overcoming of resistance is not limited to resistances to cytostatics , but that resistances to other therapeutics ( e . g . for the treatment of malaria ) are also overcome . the invention therefore relates to the use of optically pure 1 , 4 - dihydropyridines of the formula i ## str2 ## wherein r1 denotes 1 - 6c - alkyl or 1 - 4c - alkoxy - 2 - 4c - alkyl , r41 denotes hydrogen , hydroxyl , halogen , nitro , cyano , trifluoromethyl , 1 - 4c - alkyl , 1 - 4c - alkoxy , 1 - 4c - alkoxy which is completely or partly substituted by fluorine , 1 - 4c - alkoxycarbonyl , 2 - 5c - acyl , amino or mono - or di - 1 - 4c - alkylamino , r42 denotes hydrogen , hydroxyl , halogen , nitro , cyano , trifluoromethyl , 1 - 4c - alkyl , 1 - 4c - alkoxy , 1 - 4c - alkoxy which is completely or partly substituted by fluorine , 1 - 4c - alkoxycarbonyl , 2 - 5c - acyl , amino or mono - or di - 1 - 4c - alkylamino , e2 denotes straight - chain or branched 1 - 5c - alkylene , the grouping (-- ch 2 ) m -- e --( ch 2 ) n -- or the grouping -- a1 -- o -- a2 --, r5 and r6 , together and including the nitrogen atom to which they are both bonded , represent a radical of the formula ## str3 ## wherein a denotes -- ch 2 -- ch 2 -- c ( r7 ) r8 -- ch 2 -- ch 2 --, -- ch 2 -- ch 2 -- chr9 -- ch 2 -- ch 2 -- or -- ch 2 -- ch 2 -- ch 2 -- chr10 --, aryl represents a ring of the formula ## str4 ## wherein r11 and r12 are identical or different and denote hydrogen ( h ), 1 - 4c - alkyl , 1 - 4c - alkoxy , halogen , hydroxyl , trifluoromethyl or , together , methylenedioxy , and their pharmacologically tolerated salts , for the preparation of medicaments which are to be used for improving the action of antibiotics and / or cytostatics and / or for overcoming resistances to antibiotics and / or cytostatics . 1 - 6c - alkyl is straight - chain or branched and denotes , for example , a hexyl , neopentyl , isopentyl , butyl , i - butyl , sec - butyl , t - butyl , propyl , isopropyl or , in particular , ethyl or methyl radical . 1 - 4c - alkyl is straight - chained or branched and denotes , for example , a butyl , i - butyl , sec - butyl , t - butyl , propyl , isopropyl , ethyl or , in particular , methyl radical . 1 - 4c - alkoxy contains , in addition to the oxygen atom , one of the abovementioned 1 - 4c - alkyl radicals . the methoxy and the ethoxy radical are preferred . 1 - 4c - alkoxy - 2 - 4c - alkyl represents a butyl , propyl or , in particular , ethyl radical which is substituted by one of the abovementioned 1 - 4c - alkoxy radicals . the methoxyethyl radical is preferred . halogen in the context of the invention denotes bromine , fluorine and , in particular , chlorine . 1 - 4c - alkoxy which is completely or partly substituted by fluorine is , for example , 1 , 1 , 2 , 2 - tetrafluoroethoxy , trifluoromethoxy , 2 , 2 , 2 - trifluoroethoxy or , in particular , difluoromethoxy . 1 - 4c - alkoxycarbonyl contains , in addition to the carbonyl group , one of the abovementioned 1 - 4c - alkoxy radicals . 2 - 5c - acyl contains , in addition to the carbonyl group , one of the abovementioned 1 - 4c - alkyl radicals . the acetyl radical is preferred . mono - or di - 1 - 4c - alkylamino contains , in addition to the nitrogen atom , one or two of the abovementioned 1 - 4c - alkyl radicals . di - 1 - 4c - alkylamino is preferred , and here in particular dimethyl -, diethyl - or diisopropylamino . straight - chain or branched 1 - 5c - alkylene is , for example , methylene (-- ch 2 --), ethylene (-- ch 2 -- ch 2 --), trimethylene (-- ch 2 -- ch 2 -- ch 2 --), tetramethylene (-- ch 2 -- ch 2 -- ch 2 -- ch 2 --), 1 , 2 - dimethylethylene -- ch ( ch 3 )-- ch ( ch 3 )--!, 1 , 1 - dimethylethylene -- c ( ch 3 ) 2 -- ch 2 --!, 1 , 1 - dimethylpropylene -- c ( ch 3 ) 2 -- ch 2 -- ch 2 --!, 2 , 2 - dimethylethylene -- ch 2 -- c ( ch 3 ) 2 --!, isopropylidene -- c ( ch 3 ) 2 --! and 1 - methylethylene -- ch ( ch 3 )-- ch 2 --!. 2 - 4c - alkylene represents ethylene (-- ch 2 -- ch 2 --), trimethylene -- ch 2 -- ch 2 -- ch 2 --) and tetramethylene (-- ch 2 -- ch 2 -- ch 2 -- ch 2 --), ethylene being preferred . 2c - alkylenoxy - 2c - alkylene represents ethylene which is substituted by ethylenoxy (-- ch 2 -- ch 2 -- o -- ch 2 -- ch 2 --). aryl represents phenyl which is substituted by r11 and r12 . examples of aryl radicals which may be mentioned are the radicals : phenyl , 4 - methoxyphenyl , 4 - chlorophenyl , 4 - methylphenyl , 4 - fluorophenyl , 3 - fluorophenyl , 3 - chlorophenyl , 2 - chlorophenyl , 3 - methoxyphenyl , 2 - methoxyphenyl , 2 - ethoxyphenyl , 2 - methylphenyl , 3 - chloro - 4 - methylphenyl , 3 , 4 - dichlorophenyl , 3 , 6 - dichlorophenyl , 2 , 4 - dimethylphenyl , 2 , 6 - dimethylphenyl , 3 , 4 - dimethylphenyl , 3 , 4 - methylenedioxyphenyl , 2 - trifluoromethylphenyl and 3 - trifluoromethylphenyl . diaryl - 1 - 4c - alkyl is 1 - 4c - alkyl which is substituted by two aryl radicals . diaryl - 1 - 4c - alkyl is , in particular , diphenylmethyl ( benzhydryl ), or substituted benzhydryl , such as e . g . 4 , 4 &# 39 ;- difluorobenzhydryl , 4 , 4 &# 39 ;- dimethylbenzhydryl , 4 , 4 &# 39 ;- dimethoxybenzhydryl or 4 , 4 &# 39 ;- dichlorobenzhydryl . aryl - 1 - 4c - alkyl is 1 - 4c - alkyl which is substituted by aryl . benzyl and 4 - chlorobenzyl may be mentioned in particular . possible salts are all the salts with acids . the pharmacologically tolerated salts of the inorganic and organic acids which are customarily used in the pharmaceutical industry may be mentioned in particular . suitable such salts are , for example , water - soluble and water - insoluble acid addition salts , such as the hydrochloride , hydrobromide , hydriodide , phosphate , nitrate , sulphate , acetate , citrate , gluconate , benzoate , hibenzate , fendizoate , butyrate , sulphosalicylate , maleate , laurate , malate , fumarate , succinate , oxalate , tartrate , amsonate , metembonate , stearate , tosylate , 3 - hydroxy - 2 - naphthoate or mesylate . as the antibiotics , the action of which is improved or towards which resistance is overcome there may be mentioned primarily those antibiotics in which a ( growing ) development of resistance is to be observed . in this connection there may be mentioned , for example , antibiotics against bacteria , mycoses , viruses and parasites , in particular against sporozoa , and here above all malaria agents , such as , for example , amodiaquine , mefloquine , pamaquine , primaquine , tebuquine , hydroxychloroquine and , in particular , chloroquine . the cytostatics , the action of which is improved synergistically or towards which resistance is overcome are all the customary cytostatics , such as , for example , alkylating agents of the nitrogen lost derivative type ( e . g . chlorambucil , cyclophosphamide or ifosfamide ) or of the platinum complex type ( e . g . cisplatin , carboplatin , iproplatin , oxaliplatin , oxoplatin , spiroplatin or tetraplatin ), or intercalating substances of the anthracycline type ( e . g . aclarubicin , daunorubicin , doxorubicin , esorubicin , epirubicin , idarubicin , pirarubicin or zorubicin ), or mitopodozides ( e . g . etoposide ), or vinca alkaloids ( e . g . vinblastine , vincristine , vinedesine , vinepidine , vinleurosine , vinorelbine , vinrosidine , vintriptole or vinzolidine ). one embodiment ( embodiment a ) of the invention is the use of optically pure 1 , 4 - dihydropyridines of the formula i , wherein r41 denotes hydrogen , hydroxyl , halogen , nitro , cyano , trifluoromethyl , 1 - 4c - alkyl , 1 - 4c - alkoxy , 1 - 4c - alkoxy which is completely or partly substituted by fluorine , 1 - 4c - alkoxycarbonyl , 2 - 5c - acyl , amino or mono - or di - 1 - 4c - alkylamino , r42 denotes hydrogen , hydroxyl , halogen , nitro , cyano , trifluoromethyl , 1 - 4c - alkyl , 1 - 4c - alkoxy , 1 - 4c - alkoxy which is completely or partly substituted by fluorine , 1 - 4c - alkoxycarbonyl , 2 - 5c - acyl , amino or mono - or di - 1 - 4c - alkylamino , r5 and r6 , together and including the nitrogen atom to which they are both bonded , represent a radical of the formula ## str5 ## wherein a denotes -- ch 2 -- ch 2 -- c ( r7 ) r8 -- ch 2 -- ch 2 --, aryl represents a ring of the formula ## str6 ## wherein r11 and r12 are identical or different and denote hydrogen ( h ), 1 - 4c - alkyl , 1 - 4c - alkoxy , halogen , hydroxyl , trifluoromethyl or , together , methylenedioxy , and their pharmacologically tolerated salts for the preparation of medicaments which are to be used for improving the action of antibiotics and / or cytostatics and / or for overcoming resistances towards antibiotics and / or cytostatics . a further embodiment ( embodiment b ) of the invention is the use of optically pure 1 , 4 - dihydropyridines of the formula i , wherein r41 denotes hydrogen , hydroxyl , halogen , nitro , cyano , trifluoromethyl , 1 - 4c - alkyl , 1 - 4c - alkoxy , 1 - 4c - alkoxy which is completely or partly substituted by fluorine , 1 - 4c - alkoxycarbonyl , 2 - 5c - acyl , amino or mono - or di - 1 - 4c - alkylamino , r42 denotes hydrogen , hydroxyl , halogen , nitro , cyano , trifluoromethyl , 1 - 4c - alkyl , 1 - 4c - alkoxy , 1 - 4c - alkoxy which is completely or partly substituted by fluorine , 1 - 4c - alkoxycarbonyl , 2 - 5c - acyl , amino or mono - or di - 1 - 4c - alkylamino , e2 denotes the grouping --( ch 2 ) m -- e --( ch 2 ) n --, r5 and r6 , together and including the nitrogen atom to which they are both bonded , represent a radical of the formula ## str7 ## wherein a denotes -- ch 2 -- ch 2 -- c ( r7 ) r8 -- ch 2 -- ch 2 --, -- ch 2 -- ch 2 -- chr9 -- ch 2 -- ch 2 -- or -- ch 2 -- ch 2 -- ch 2 -- chr10 --, aryl represents a ring of the formula ## str8 ## wherein r11 and r12 are identical or different and denote hydrogen ( h ), 1 - 4c - alkyl , 1 - 4c - alkoxy , halogen , hydroxyl , trifluoromethyl or , together , methylenedioxy , and their pharmacologically tolerated salts for the preparation of medicaments which are to be used for improving the action of antibiotics and / or cytostatics and / or for overcoming resistances towards antibiotics and / or cytostatics . a further embodiment ( embodiment c ) of the invention is the use of optically pure 1 , 4 - dihydropyridines of the formula i , wherein r41 denotes hydrogen , hydroxyl , halogen , nitro , cyano , trifluoromethyl , 1 - 4c - alkyl , 1 - 4c - alkoxy , 1 - 4c - alkoxy which is completely or partly substituted by fluorine , 1 - 4c - alkoxycarbonyl , 2 - 5c - acyl , amino or mono - or di - 1 - 4c - alkylamino , r42 denotes hydrogen , hydroxyl , halogen , nitro , cyano , trifluoromethyl , 1 - 4c - alkyl , 1 - 4c - alkoxy , 1 - 4c - alkoxy which is completely or partly substituted by fluorine , 1 - 4c - alkoxycarbonyl , 2 - 5c - acyl , amino or mono - or di - 1 - 4c - alkylamino , e2 denotes straight - chain or branched 1 - 5c - alkylene , the grouping --( ch 2 ) m -- e --( ch 2 --) n -- or the grouping -- a1 -- o -- a2 --, r5 and r6 , together and including the nitrogen atom to which they are both bonded , represent a radical of the formula ## str9 ## wherein a denotes -- ch 2 -- ch 2 -- c ( r7 ) r8 -- ch 2 -- ch 2 --, -- ch 2 -- ch 2 -- chr9 -- ch 2 -- ch 2 -- or -- ch 2 -- ch 2 -- ch 2 -- chr10 --, aryl represents a ring of the formula ## str10 ## wherein r11 and r12 are identical or different and denote hydrogen ( h ), 1 - 4c - alkyl , 1 - 4c - alkoxy , halogen , hydroxyl , trifluoromethyl or , together , methylenedioxy , and their pharmacologically tolerated salts for the preparation of medicaments which are to be used for improving the action of antibiotics and / or cytostatics and / or for overcoming resistances towards antibiotics and / or cytostatics . subject matter of the invention which is to be singled out is the use according to the invention of compounds of the formula i , wherein r5 and r6 , together and including the nitrogen atom to which they are both bonded , represent a radical of the formula ## str11 ## wherein a denotes -- ch 2 -- ch 2 -- c ( r7 ) r8 -- ch 2 -- ch 2 --, -- ch 2 -- ch 2 -- chr9 -- ch 2 -- ch 2 -- or -- ch 2 -- ch 2 -- ch 2 -- chr10 --, subject matter of the invention which is to be especially singled out is the use according to the invention of compounds of embodiments a , b and c , wherein the substituents and symbols have the meanings given for the subject matter of the invention which is to be singled out . preferred subject matter of the invention is the use according to the invention of compounds of the formula i , wherein r5 and r6 , together and including the nitrogen atom to which they are both bonded , represent a radical of the formula ## str12 ## wherein a denotes -- ch 2 -- ch 2 -- c ( r7 ) r8 -- ch 2 -- ch 2 --, compounds which are particularly suitable for the use according to the invention can be seen from the following table i , in which the corresponding compounds of the formula i are shown with the particular substituent definitions : table i__________________________________________________________________________ ## str13 ## ## str14 ## ## str15 ## ## str16 ## ## str17 ## ## str18 ## ## str19 ## __________________________________________________________________________ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str20 ## och . sub . 2 ch . sub . 2 ch . sub . 2 ## str21 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str22 ## och . sub . 2 ch . sub . 2 ch . sub . 2 ## str23 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str24 ## och . sub . 2 ch . sub . 2 ch . sub . 2 ## str25 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str26 ## och . sub . 2 ch . sub . 2 ## str27 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str28 ## och . sub . 2 ch . sub . 2 ch . sub . 2 ## str29 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str30 ## och . sub . 2 ch . sub . 2 ch . sub . 2 ## str31 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str32 ## och . sub . 2 ch . sub . 2 ch . sub . 2 ## str33 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str34 ## och . sub . 2 ch . sub . 2 ch . sub . 2 ## str35 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str36 ## och . sub . 2 ch . sub . 2 ch . sub . 2 ## str37 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str38 ## och . sub . 2 chchch . sub . 2 ## str39 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str40 ## och . sub . 2 ccch . sub . 2 ## str41 ## ch . sub . 3 ch . sub . 3 ch . sub . 3 ## str42 ## o ( ch . sub . 2 ). sub . 2 o ( ch . sub . 2 ). sub . 2 ## str43 ## __________________________________________________________________________ the compounds of the formula i are known , for example from ep - a - 242 829 , ep - a - 296 316 , de - os 36 27 742 and wo88 / 07531 . the compounds of the formula i and their pharmacologically tolerated salts have useful properties which render them commercially usable in the context according to the invention . they improve the action of antibiotics and cytostatics in a synergistic manner , and moreover they are capable of overcoming resistances towards antibiotics and cytostatics which already exist or occur in the course of therapy . the invention thus relates to the use of compounds of the formula i in combination with antibiotics or cytostatics in antibiotic and / or cytostatic therapy . the invention furthermore relates to the use of compounds of the formula i for the preparation of medicaments which are to be employed in combination with antibiotics or cytostatics in antibiotic and / or cytostatic therapy . in overcoming resistance towards antibiotics , it is of particular importance to overcome resistance towards chloroquine , since the increasing development of resistance of plasmodium falciparum ( the pathogen of malaria tropica ) towards this proven malaria agent in some parts of the world presents increasing difficulties in combating malaria . in improving the action of or overcoming the development of resistance towards cytostatics , it is of particular importance that the dose of the cytostatics administered can be reduced , which leads to a significant reduction in toxic side effects , and that the number of cytostatics which can be employed is increased , so that the cytostatic of optimum suitability for the particular tumour and the particular patient can be selected in a targeted manner . it should be pointed out in this connection that because of the small influence of the compounds i on the cardiovascular system , e . g . on blood pressure and heart rate , these compounds can be administered in therapeutically active doses without the risk of undesirable side effects on the cardiovascular system . the excellent activity of compounds of the formula i and their pharmacologically tolerated salts enables them to be used in human medicine as active compounds in antibiotic and cytostatic therapy , it being possible for the compounds of the formula i to be administered together with the antibiotics or cytostatics in a specified dose in the form of combination preparations , or it being possible for the compounds of the formula i to be employed separately , in any desired dosage and a suitable presentation form , as concomitant and assisting active compounds in antibiotic or cytostatic therapy . the ratio of compound i to antibiotic or cytostatic depends on the disease to be treated , the state of the disease in the patient and the antibiotic or cytostatic used . it has in general proved advantageous here to administer the compounds of the formula i in a daily dose of about 0 . 5 to 30 mg / kg of body weight for oral administration and in a daily dose of about 0 . 1 to 10 mg / kg of body weight for intravenous administration , if desired in the form of several individual doses or as a continuous infusion , in order to achieve the desired result . the antibiotics or cytostatics are administered in the doses customary for them , but preferably in lower doses . the particular optimum dosage and mode of administration required for the active compounds can be specified by any expert on the basis of his expert knowledge . the ability of compounds of the formula i to overcome the resistance of tumour cells towards cytostatics was demonstrated on various tumour cell lines . for this , a selected compound of the formula i , the compound (-)- 1 , 4 - dihydro - 2 , 6 - dimethyl - 4 -( 3 - nitrophenyl )- pyridine - 3 , 5 - dicarboxylic acid 3 - methyl 5 - 3 ( 4 , 4 - diphenyl - 1 - piperidinyl )- propyl ! ester hydrochloride (= compound 1 ), was investigated in more detail as follows : the tumour cell lines molt / vcr - 5 × 9 ( starting density : 1 . 14 × 10 6 cells / ml ), molt / dau - 8 ( starting density : 1 . 01 × 10 6 cells / ml ) and ccrf cemvcr1000 +( starting density : 2 . 00 × 10 6 cells / ml ), which are resistant towards the cytostatics vincristine and daunomycin , were incubated for 72 . 5 to 73 . 25 hours in accordance with the following test pattern : 2 . control with the cytostatic relating to the particular cell line ( for the concentrations , see below ) 4 . compound 1 in concentrations of 10 - 6 and 10 - 7 m 5 . compound 1 in concentrations of 10 - 6 and 10 - 7 m , together with the cytostatic relating to the particular cell line ( for the concentrations , see below ). the percentage reduction in cell counts ( given in % of the dmso control ) on addition of the cytostatic by itself , compound 1 in concentrations of 10 - 7 m or 10 - 6 m by itself , and cytostatic + compound 1 in concentrations of 10 - 7 m or 10 - 6 m is as shown in table 2 : table 2__________________________________________________________________________intensification of the cytotoxicity of cytostatics by compound 1 ; percentagegrowth inhibition of tumour cell lines in comparison with the dmsocontrol molt / vcr - cell line : 5 × 9 molt / dau - 8 ccrf cem vcr1000 + cytostatic : vincristine daunomycin vincristine concentration ! 5 × 10 . sup .- 9 m ! 10 . sup .- 8 m ! 1 . 08 × 10 . sup .- 6 m ! active compound concentration ! growth inhibition in % __________________________________________________________________________cytostatic by itself 0 0 0compound 1 10 . sup .- 7 m ! 66 43 10by itselfcompound 1 10 . sup .- 7 m ! + 99 56 65cytostaticcompound 1 p10 . sup .- 5 m ! 79 53 67by itselfcompound 1 10 . sup .- 5 m ! + 99 96 90cytostatic__________________________________________________________________________ the following can be seen from the values shown in table 2 : when the cytostatics are added by themselves , no growth inhibition at all is to be observed , and the tumour cell lines are resistant towards the cytostatics . all resistant cells are inhibited in their growth by addition of compound 1 by itself . this inhibition of growth depends on the concentration . by addition of compound 1 together with the cytostatic , the resistance towards cytostatics is overcome and the cytotoxicity of the cytostatics is intensified .
optically pure diaryl compounds of formula , in which the substituents and symbols have the meanings indicated in the description are proposed as active ingredients in medicinal preparations for treating tumorous diseases . ## str1 ##