The present invention concerns new substrates for an enzyme especially an enzyme the substrate of which is a xenobiotic such as a drug or a pesticide. Xenobiotics are substances that are foreign for the human or animal body. Usually, these substances are metabolized in the human or animal body. Especially in the small intestine and the liver there are enzyme systems that modify the xenobiotics such that they become more water soluble. Drugs often lose their pharmacological effect during this modification. Due to the higher solubility in water the drugs lose their ability to enrich in the body and they are excreted quickly via the kidney.

The enzyme systems usually work in two phases. In phase I the xenobiotics are functionalized, i.e., they are provided with a reactive chemical group. In phase II this chemical group is coupled with a strongly water soluble substance such as glucuronic acid or sulfuric acid. The most important enzymes of the phase I metabolism are the cytochrome P450 enzymes (CYP enzymes) that are involved in the oxidation of more than 90 % of all therapeutically important drugs.

The activity of the enzymes that are involved in phase I me- tabolism is of major importance for the plasma concentration of xenobiotics. Drugs or other substances may inhibit or induce the activity of these enzymes. Practically very important is the influence of drugs on the degradation of other drugs by an inhibition or induction of CYP enzymes. The inhi- bition of the metabolism of drugs with a narrow therapeutical range such as cyclosporine and phenprocoumon may have serious side effects.

Known strong inhibitors of CYP enzymes are the azole antimy- cotics ketoconazole and itraconazole as well as the macrolide antibiotics clarithromycin and erythromycin. Substances which shall be used such that they can be taken up by the human or animal body and which inhibit enzymes that are involved in the metabolism of xenobiotics may seriously influence the ef- feet of the xenobiotics. Therefore, it is important to examine the inhibitory activity of the substances on these enzymes. The substances may be drugs, plant extracts, secondary plant metabolites, or pesticides.

From Unger M. and Frank, A., Rapid Commun. Mass Spectrom.

2004, 18, pages 2273-2281 a simultaneous determination of the inhibitory potency of herbal extracts on the activity of six major cytochrome P450 enzymes using liquid chromatogra- phy/mass spectrometry and automated online extraction is known. For the determination of the inhibitory activity substrates were incubated with a commercially available mixture of CYP1A2/2C8/2C9/2C19/2D6 and 3A4 and the resulting metabolites were quantified with liquid chromatography and mass spectrometry.

From US 6,420,131 Bl novel fluorescent substrates of human cytochromes P450 enzymes are known. These substrates are useful in assessing cytochrome P450 enzyme activity and in selecting compounds which inhibit cytochrome P450 enzyme activ- ity and, in particular, for identifying potential adverse drug interactions which are mediated by inhibition of cytochrome P450 enzyme activity.

From Takasu, K. et al . , Bioorganic and Medicinal Chemistry Letters 14 (2004), pages 1689-1692 and Takasu, K. et al . ,

Chem. Pharm. Bull. (2005), 53(6), pages 653-661 π-delocalized β-carbolinium cations as potential antimalarials are known.

The most important phase II reaction is the conjugation with glucuronic acid which is also called glucuronidation . About 10% of the 200 drugs prescribed most frequently throughout the world become at least partly glucuronidated. Glucuronida- tions are catalyzed by uridine 5 ' -diphosphate (UDP) glucuro- nosyltransferases (UGTs) . UGTs transfer UDP-glucuronic acid to substrates. The substrates may be drugs or their phase I metabolites. The glucuronidation increases water solubility of the substrates and enables their excretion via the kidney. UGTs show a low specificity with respect to the substrate. The most relevant UGTs with respect to the metabolism of drugs are UGTlAl, UGT1A3, UGT1A4, UGT1A6, UGT1A7, UGT1A8, UGT1A9 and UGTlAlO as well as UGT2B4, UGT2B7, UGT2B15 and UGT2B17. UGTlAl and UGT2B7 are involved in glucuronidation of numerous drugs such as codeine, morphine and oxazepam ((RS)- 9-chloro-4-hydroxy-6-phenyl-2, 5-diazabicyclo[5.4.0] undeca- 5, 8, 10, 12-tetraen-3-one) .

An object of the present invention is to provide a use of a substrate for enzymes involved in phase I or phase II metabolism, a method for synthesizing this substrate, and sub- strates for the enzymes as well as metabolites of the enzymes. The reaction product of the reaction of the enzymes and the substrate shall be detectable by its fluorescence or its mass.

The object of the present invention is solved by the subject matter of claims 1, 17 and 24. Embodiments are subject matter of claims 2 to 16 and 18 to 23.

The invention concerns the use of a first compound of formula

or

wherein

R ¹ , R ³ to R ⁶ , R ⁸ and R ⁹ represent independently for each occurrence -H, Ci-Cis-alkyl, C ₂ -Ci ₈ -alkenyl, an aryl residue, a heteroaryl residue, a carboxyl group or an ester of a carbox- yl group, a benzyl group, a carboxybenzyl group, an amide group, an acyl group, an alkoxy substituent, an alkyl group bound via a sulfur atom, a sulfonyl group, a nitrogen substituent, a nitrogen substituent bound via a sulfur atom, a hy- droxyl group, fluorine, chlorine, bromine, iodine, -CN, -CF ₃ , or -(CHz) _n -O-R' ', wherein n = 0-18 and R' ' represents Ci-Ci ₈ - alkyl, C ₂ -Ci ₈ -alkenyl, benzyl, an aryl or a heteroaryl residue,

R ² represents -H, Ci-Ci ₈ -alkyl, C ₂ -Ci ₈ -alkenyl, an aryl residue, a heteroaryl residue, a sulfonyl group, a benzyl group, a carboxybenzyl group, or - (CH ₂ ) _n -O-R' ', wherein n = 0-18 and R' ' represents Ci-Ci ₈ -alkyl, C ₂ -Ci ₈ -alkenyl, benzyl, an aryl or a heteroaryl residue, and

R ⁷ represents -H, Ci-Ci ₈ -alkyl, C ₂ -Ci ₈ -alkenyl, an aryl resi- due, a heteroaryl residue, a benzyl group, a carboxybenzyl group, an acyl group, or - (CH ₂ ) _n -0-R' ', wherein n = 0-18 and R' ' represents Ci-Ci ₈ -alkyl, C ₂ -Ci ₈ -alkenyl, benzyl, an aryl or a heteroaryl residue,

wherein X ^~ is a counterion

as substrate for a cytochrome P450 enzyme or an uridine 5'- diphosphate glucuronosyltransferase (UGT) .

Independently for each occurrence all alkyl and alkenyl groups of the first compound may be branched, unbranched or cyclic. Furthermore, independently for each occurrence the carboxyl group may be -COOR ¹⁰ , wherein R ¹⁰ represents Ci-Ci ₈ - alkyl, C ₂ -Ci ₈ -alkenyl, a benzyl group, an aryl group, or a he- teroarylgroup . If the first compound can act as an acid, i.e., if it can undergo a deprotonation, the use also comprises the use of the conjugate base of the first compound.

The reaction product of the substrate can be detected by its fluorescence or its mass. Fluorescence can be detected in a microtiter plate or after chromatography, especially high performance liquid chromatography (HPLC) . It is also possible to detect the mass of the reaction product by mass spectrometry after chromatography, especially HPLC. Thus, the first compound can be used for the in vitro examination of synthetic or herbal drugs or other xenobiotics with respect to their ability to inhibit activity of said enzymes. Especially the first compound can be used for the in vitro identification of drug interactions that are due to an inhibition of a CYP en- zyme . The reaction product of the first compound exhibits a strong fluorescence at pH 8 or higher. A positive charge at the nitrogen atom allows a chromatography on a reversed phase col- umn at such a pH. Chromatography enables the separation of the reaction product from substances that interfere with the detection of the reaction product, e.g., due to an own fluorescence or quenching. Especially substances of herbal origin, quench the fluorescence of the reaction product or exhi- bit an own fluorescence that cannot be separated from the fluorescence of the reaction product. A chromatographical separation of the reaction product from a substance to be tested for its activity allows the detection of the reaction product without the influence of this substance. The chroma- tographic separation at pH 8 or higher followed by detection of the fluorescence allows a very sensitive detection of the reaction product.

The first compound has a very high affinity to said enzymes involved in phase I and phase II metabolism, i.e., a low K _m value. The K _m value that is also designated as Michaelis- Menten constant is the concentration of a substrate of an enzyme at which the half maximal reaction velocity is reached. Furthermore, the first compound is metabolized at a relative- Iy high reaction velocity. Due to the high affinity to the enzymes the first compound can be used as a substrate of the enzymes at a relatively low concentration such that no precipitation of the first compound occurs in the solution in which the enzymatic reaction takes place. Due to the rela- tively high reaction velocity the reaction product is produced in an amount that is sufficient for a quantitative detection within a reasonable time.

Due to the quaternary nitrogen atom the first compound can also be detected very specifically with high sensitivity by mass spectrometry. Thus, the first compound can be used in different types of assays and with different detection methods with high sensitivity and specificity.

In some embodiments the Ci-Ci ₈ -alkyl, the C ₂ -Ci ₈ -alkenyl, the aryl residue, the heteroaryl residue, and the benzyl group are independently for each occurrence unsubstituted, mono- substituted, or polysubstituted. The aryl residue may be phenyl or naphthyl and the hetero aryl residue may be benzox- azole, benzothiazole, furane, imidazole, oxazole, pyridazin, pyridin, pyrimidin, pyrrol, tetrazole, thiazole, thiophen or triazole. The acyl group can be a formyl group, an acetyl group, a trichloroacetyl group, a fumaryl group, a maleyl group, a succinyl group, a benzoyl group, a branched acyl group or a branched aryl-substituted or heteroaryl- substituted acyl group. The alkoxy substituent may be -O- methyl, -O-ethyl, -O-n-propyl, -O-isopropyl, -O-n-butyl, -O- isobutyl, -O-sec-butyl, or -0- tert-butyl . The alkyl group bound via the sulfur atom may be methyl or ethyl. In some em- bodiments the sulfonyl group is -SO ₃ H, -SO ₂ CH ₃ , -SO ₂ CF ₃ , -

SO ₂ C ₆ H ₄ CH ₃ , -SO ₂ C ₆ H ₄ COOH, or -SO ₂ C ₆ H ₄ CH ₂ Br. The nitrogen substituent may be -NH ₂ , -NC, -NO ₂ , -N-CO-R, -NHR, -NRR', and the nitrogen substituent bound via a sulfur atom may be -SO ₂ NH ₂ , -SO ₂ NHR, -SO ₂ NRR' , wherein R and R' represent independently for each occurrence Ci-Ci ₈ -alkyl, C ₂ -Ci ₈ -alkenyl, benzyl, an aryl or a heteroaryl residue.

In some embodiments the substituents R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ , and/or R ⁹ are independently for each occurrence halo- genated and/or R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , R, R' and/or R' ' are independently for each occurrence covalently linked via a further Ci-Ci ₈ -alkyl, C ₂ -Ci ₈ -alkenyl, benzyl, aryl, or heteroaryl residue, wherein none of the Ci-Ci ₈ -alkyls or C ₂ -Ci ₈ alkenyls is covalently linked via the further Ci-Ci ₈ -alkyl or C ₂ -Ci ₈ alkenyl. The linkage may be a linkage to one of the C-, N-, or O-atoms of the first compound or of one of the substi- tuents. The halogenated substituents may be represented by - CF ₃ , -CH ₂ -CH ₂ -Cl, or -C ₆ F ₅ and the covalently linked substituents including their linkages may be represented by -CH ₂ -C ₆ H ₄ - COOH, or -(CHz) ₃ -O-CH ₂ -CH ₃ .

The counterion may be iodide, bromide, chloride, trifluoroa- cetate, perchlorate, tetrafluoroborate, sulfate or phosphate.

In certain embodiments

R ² = benzyl, R ⁷ = -CH ₃ or -C ₂ H ₅ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ or benzyl, or

R ² = -CH ₃ , -C ₂ H ₅ , or benzyl, R ⁷ = benzyl, R ¹ = -CH ₃ , R ³ -R ⁶ and

R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ , or benzyl, or R ² and R ⁷ = -C ₂ H ₅ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H,

-CH ₃ , -C ₂ H ₅ , or benzyl, or

R ² = -CH ₃ , R ⁷ = -C ₂ H ₅ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ =

-H, -CH ₃ , -C ₂ H ₅ , or benzyl, or

R ² = -C ₂ H ₅ , R ⁷ = -CH ₃ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ , or benzyl, or

R ² = -CH ₃ , -C ₂ H ₅ , or benzyl, R ⁷ = -C ₅ H ₁₁ , R ¹ = -CH ₃ , R ³ -R ⁶ and

R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ , or benzyl, or

R ² and R ⁷ = -CH ₃ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H,

-CH ₃ , -C ₂ H ₅ , or benzyl, or R ² = -H, -CH ₃ , or -C ₂ H ₅ , R ¹ and R ⁷ = -CH ₃ , R ⁹ = 3-carboxybenzyl or 4-carboxybenzyl, and R ³ -R ⁶ and R ⁸ = -H.

R ² and the counterion may also be absent in the first com ^¬ pound. If R ² is absent the nitrogen atom is not charged.

A dimer may be formed from two first compounds of formula 1, two first compounds of formula 2, or one first compound of formula 1 and one first compound of formula 2, wherein both first compounds are linked via a - (CH ₂ ) _n - group, wherein n = 0 - 18, wherein the - (CH ₂ ) _n - group replaces in both first compounds independently for each of the first compounds one of the residues R ¹ to R ⁹ . The dimer can be used instead of the first compound as substrate for said enzymes involved in phase I or phase II metabolism.

The use of the first compound as a substrate for cytochrome P450 enzyme or UGT may be for testing a test compound for its inhibitory activity on said enzymes. The use can comprise the following steps:

a) Incubating the first compound, the cytochrome P450 enzyme or the UGT and if necessary a coenzyme for the reaction of the cytochrome P450 enzyme or the UGT and the first compound in the presence and the absence of the test compound and

bl) performing a first measurement of a UV-absorption or a fluorescence of the reaction product of the first compound generated in presence of the test compound and performing a second measurement of a UV-absorption or a fluorescence of the reaction product of the first compound generated in absence of the test compound,

or

b2) performing a first measurement of a mass of the reaction product of the first compound generated in presence of the test compound and performing a second measurement of a mass of the reaction product of the first compound generated in absence of the test compound,

and

c) comparing the results of the first measurement and the second measurement. The first measurement of a mass of the reaction product of the first compound and the second measurement of a mass of the reaction product of the first compound may comprise a quantitation of the reaction product.

Said enzymes involved in phase I or phase II metabolism may be human enzymes. In certain embodiments the cytochrome P450 enzyme is a cytochrome P450 enzyme 1A2 (CYP1A2), IAl (CYPlAl), 2A6 (CYP2A6) , IBl (CYPlBl), 2B6 (CYP2B6) , 2C8 (CYP2C8), 2C9 (CYP2C9) , 2C18 (CYP2C18), 2C19 (CYP2C19), 2D6 (CYP2D6) , 2J2 (CYP2J2), 2El (CYP2E1), 3A4 (CYP3A4), 3A5 (CYP3A5), 3A7 (CYP3A7), 4F2 (CYP4F2) or 19 (CYP19) . The uridine 5 ' -diphosphate glucuronosyltransferase (UGT) may be an UGTlAl, UGT1A3, UGT1A4, UGT1A6, UGT1A7, UGT1A8, UGT1A9, UGTlAlO, UGT2B4, UGT2B7, UGT2B15 or UGT2B17.

A chromatography may be performed between steps a) and bl) or steps a) and b2) . In case of a test compound to be tested which influences the first measurement, e.g., because it has an own fluorescence in the same range of wavelength as the reaction product of the first compound, the chromatography is necessary to enable the first measurement or it simplifies the first measurement and/or it makes it more accurate.

The invention also concerns a method for synthesizing the first compound, wherein a second compound for formula

R ⁵ R ⁴

or

R ⁵ R ⁴

is reacted with an alkylating reagent or a benzylation reagent in a solvent.

In some embodiments the second compound is reacted with the alkylating reagent or the benzylation reagent in the presence of a base. If the second compound is reacted with the alkylating reagent or the benzylation reagent in the presence of a base the first compound is generated as a direct reaction product. If it is reacted in the absence of a base an inter- mediate product is generated with very high yield that can be converted into the first compound easily.

In certain embodiments the second compound of formula 3 is 1- methyl-9H-pyrido [3, 4-£>] indole-7-ol (R ¹ = -CH ₃ , R ² - R ⁹ = -H) or 7-methoxy-l-methyl-9H-pyrido [3, 4-£>] indole (R ¹ , R ⁷ = -CH ₃ , R ² - R ⁶ , R ⁸ , R ⁹ = -H) or a salt of these compounds and the second compound of formula 4 is l-methyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indole-7-ol (R ¹ = -CH ₃ , R ² - R ⁹ = -H) or 7- methoxy-l-methyl-4, 9-dihydro-3H-pyrido [3, 4-£>] indole (R ¹ , R ⁷ = -CH ₃ , R ² - R ⁶ , R ⁸ , R ⁹ = -H) or a salt of these compounds.

The benzylation reagent may be benzyl halogenide or carbox- ybenzyl halogenide, wherein the halogenide may be chloride, bromide, or iodide and the alkylating reagent may be dimethyl sulfate, diethyl sulfate or diazomethane, alkyl halogenide, wherein the halogenide may be chloride, bromide, or iodide, alkyl triflate, alkyl tosylate, alkyl mesylate, or aryl trif- late, wherein the aryl may be phenyl or naphthyl .

The base can be diethylamine, triethylamine, sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide. In some embodiments the solvent is tetrahydrofuran, acetone, dimethyl sulfoxide, acetonitrile, chloroform, dich- loromethane or dimethyl formamide. The method according to the invention is very effective if the second compound is reacted with the alkylating reagent or the benzylation reagent at a temperature ranging from 0 to 80 ⁰ C.

The invention further concerns a compound, wherein the compound is a first compound as specified above, wherein

R ² = benzyl, R ⁷ = -CH ₃ or -C ₂ H ₅ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ or benzyl, or

R ² = -CH ₃ , -C ₂ H ₅ , or benzyl, R ⁷ = benzyl, R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ , or benzyl, or

R ² and R ⁷ = -C ₂ H ₅ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ , or benzyl, or

R ² = -CH ₃ , R ⁷ = -C ₂ H ₅ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ , or benzyl, or

R ² = -C ₂ H ₅ , R ⁷ = -CH ₃ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ , or benzyl, or

R ² = -CH ₃ , -C ₂ H ₅ , or benzyl, R ⁷ = -C ₅ H ₁₁ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ , or benzyl, or R ² and R ⁷ = -CH ₃ , R ¹ = -CH ₃ , R ³ -R ⁶ and R ⁸ = -H, and R ⁹ = -H, -CH ₃ , -C ₂ H ₅ , or benzyl, or

R ² = -H, -CH ₃ , or -C ₂ H ₅ , R ¹ and R ⁷ = -CH ₃ , R ⁹ = 3-carboxybenzyl or 4-carboxybenzyl, and R ³ -R ⁶ and R ⁸ = -H

or wherein the compound is a compound of formula

1a 1b

2a or 2b Counterions are not shown in the above formulas but it is understood that the compound may comprise a counterion.

If the compound as specified above is a first compound ac- cording to formula 1 as specified above, the compound may be

2-benzyl-7-methoxy-l-methyl-9H-pyrido [3, 4-£>] indole-2-ium,

2-benzyl-7-methoxy-l , 9-dimethyl-9H-pyrido [3, 4-£>] indol-2-ium,

2-benzyl-9-ethyl-7-methoxy-l-methyl-9H-pyrido [3, 4-£>] indol-2- ium,

2, 9-dibenzyl-7-methoxy-l-methyl-9H-pyrido [3, 4-£>] indol-2-ium,

2-benzyl-7-ethoxy-l-methyl-9H-pyrido [3, 4-£>] indole-2-ium,

2-benzyl-7-ethoxy-l, 9-dimethyl-9H-pyrido [3, 4-£>] indol-2-ium,

2-benzyl-7-ethoxy-9-ethyl-l-methyl-9H-pyrido [3, 4-£>] indol-2- ium,

2, 9-dibenzyl-7-ethoxy-l-methyl-9H-pyrido [3, 4-£>] indol-2-ium,

2-benzyl-7- (benzyloxy) -l-methyl-9H-pyrido [3, 4-£>] indole-2-ium,

2-benzyl-7- (benzyloxy) -1, 9-dimethyl-9H-pyrido [3, 4-£>] indol-2- ium, 2-benzyl-7- (benzyloxy) -9-ethyl-l-methyl-9H-pyrido [3, 4- jb] indol-2-ium,

2, 9-dibenzyl-7- (benzyloxy) -l-methyl-9H-pyrido [3, 4-i>] indol-2- iumm,

7- (benzyloxy) -1, 2-dimethyl-9H-pyrido [3, 4-i>] indol-2-ium 7- (benzyloxy) -1,2, 9-trimethyl-9H-pyrido [3, 4-£>] indol-2-ium,

7- (benzyloxy) -9-ethyl-l, 2-dimethyl-9H-pyrido [3, 4-i>] indol-2- ium,

9-benzyl-7- (benzyloxy) -1, 2-dimethyl-9H-pyrido [3, 4-£>] indol-2- ium, 7- (benzyloxy) -2-ethyl-l-methyl-9H-pyrido [3, 4-i>] indol-2-ium,

7- (benzyloxy) -2-ethyl-l, 9-dimethyl-5H-pyrido [3, 4-£>] indol-2- ium,

7- (benzyloxy) -2, 9-diethyl-l-methyl-9H-pyrido [3, 4-i>] indol-2- ium, 9-benzyl-7- (benzyloxy) -2-ethyl-l-methyl-9H-pyrido [3, 4- b] indol-2-ium,

7 -ethoxy-2 -ethyl - l -methyl - 9H-pyrido [ 3 , 4 -£>] indol -2 - ium, 7-ethoxy-2-ethyl-l, 9-dimethyl-9H-pyrido [3, A-b] indol-2-ium,

7-ethoxy-2, 9-diethyl-l-methyl-9H-pyrido [3, A-b] indol-2-ium,

9-benzyl-7-ethoxy-2-ethyl-l-methyl-9H-pyrido [3, A-b] indol-2- ium, 7-ethoxy-l, 2-dimethyl-9H-pyrido [3, A-b] indol-2-ium,

7-ethoxy-l, 2, 9-trimethyl-9H-pyrido [3, A-b] indol-2-ium,

7-ethoxy-9-ethyl-l, 2-dimethyl-9H-pyrido [3, A-b] indol-2-ium,

9-benzyl-7-ethoxy-l, 2-dimethyl-9H-pyrido [3, A-b] indol-2-ium,

2-ethyl-7-methoxy-l-methyl-9H-pyrido [3, A-b] indole-2-ium 2-ethyl-7-methoxy-l, 9-dimethyl-9H-pyrido [3, A-b] indol-2-ium,

2, 9-diethyl-7-methoxy-l-methyl-9H-pyrido [3, A-b] indol-2-ium,

9-benzyl-2-ethyl-7-methoxy-l-methyl-5H-pyrido [3, A-b] indol-2- ium,

1, 2-dimethyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2-ium, 1,2, 9-trimethyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2-ium,

9-ethyl-l, 2-dimethyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2- ium,

9-benzyl-l, 2-dimethyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2- ium, 2-ethyl-l-methyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2-ium,

2 -ethyl- 1, 9-dimethyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2- ium,

2, 9-diethyl-l-methyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2- ium, 9-benzyl-2-ethyl-l-methyl-7- (pentyloxy) -9H-pyrido [3, A- b] indol-2-ium,

2-benzyl-l-methyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2-ium,

2-benzyl-l, 9-dimethyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2- ium, 2-benzyl-9-ethyl-l-methyl-7- (pentyloxy) -9H-pyrido [3, A- b] indol-2-ium,

2, 9-dibenzyl-l-methyl-7- (pentyloxy) -9H-pyrido [3, A-b] indol-2- ium,

7-methoxy-l, 2-dimethyl-9H-pyrido [3, A-b] indol-2-ium, 7-methoxy-l, 2, 9-trimethyl-9H-pyrido [3, A-b] indol-2-ium,

9-ethyl-7-methoxy-l, 2-dimethyl-9H-pyrido [3, A-b] indol-2-ium,

9-benzyl-7-methoxy-l , 2-dimethyl-9H-pyrido [3, A-b] indol-2-ium, 9- (4-carboxybenzyl) -7-methoxy-l -methyl- 9H-pyrido [3, 4-£>] indol-

2-ium,

9- (4-carboxybenzyl) -7-methoxy-l, 2-dimethyl-9H-pyrido [3, 4- b] indol-2-ium, 9- (4-carboxybenzyl) -2-ethyl-7-methoxy-l-methyl-9H-pyrido [3, 4- b] indol-2-ium,

2-benzyl-9- (4-carboxybenzyl) -7-methoxy-l-methyl-9H- pyrido [3, 4-£>] indol-2-ium,

9- (3-carboxybenzyl) -7-methoxy-l-methyl-9H-pyrido [3, 4-£>] indol- 2-ium,

9- (3-carboxybenzyl) -7-methoxy-l, 2-dimethyl-9H-pyrido [3, 4- jb] indol-2-ium,

9- (3-carboxybenzyl) -2-ethyl-7-methoxy-l-methyl-9H-pyrido [3, 4- b] indol-2-ium, or 2-benzyl-9- (3-carboxybenzyl) -7-methoxy-l-methyl-9H- pyrido [3, 4-i>] indol-2-ium.

If the compound as specified above is a first compound according to formula 2 as specified above, the compound may be

2-benzyl-7-methoxy-l-methyl-4 , 9-dihydro-3H-pyrido [3, 4- b] indole-2-ium,

2-benzyl-7-methoxy-l , 9-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol -2 - ium, 2 -benzyl - 9-ethyl - 7 -methoxy- l -methyl - 4 , 9-dihydro- 3H- pyrido [ 3 , 4 -£>] indol -2 - ium,

2, 9-dibenzyl-7-methoxy-l-methyl-4 , 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

2-benzyl-7-ethoxy-l-methyl-4 , 9-dihydro-3H-pyrido [3, 4- b] indole-2-ium,

2-benzyl-7-ethoxy-l , 9-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

2-benzyl-7-ethoxy-9-ethyl-l-methyl-4 , 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium, 2, 9-dibenzyl-7-ethoxy-l-methyl-4 , 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium, 2-benzyl-7- (benzyloxy) -l-methyl-4, 9-dihydro-3H-pyrido [3, 4- b] indole-2-ium,

2-benzyl-7- (benzyloxy) -1, 9-dimethyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium, 2-benzyl-7- (benzyloxy) -9-ethyl-l-methyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium,

2, 9-dibenzyl-7- (benzyloxy) -l-methyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-iumm,

7- (benzyloxy) -1, 2-dimethyl-4, 9-dihydro-3H-pyrido [3, 4-£>] indol- 2-ium

7- (benzyloxy) -1,2, 9-trimethyl-4, 9-dihydro-3H-pyrido [3, 4- jb] indol-2-ium,

7- (benzyloxy) -9-ethyl-l, 2-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium, 9-benzyl-7- (benzyloxy) -1, 2-dimethyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium,

7- (benzyloxy) -2-ethyl-l-methyl-4, 9-dihydro-3H-pyrido [3, 4- jb] indol-2-ium,

7- (benzyloxy) -2-ethyl-l, 9-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- jb] indol-2-ium,

7- (benzyloxy) -2, 9-diethyl- l-methyl-4, 9-dihydro-3H-pyrido [3, 4- jb] indol-2-ium,

9-benzyl-7- (benzyloxy) -2-ethyl-l-methyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium, 7-ethoxy-2-ethyl-l-methyl-4, 9-dihydro-3H-pyrido [3, 4-jb] indol- 2-ium,

7-ethoxy-2-ethyl-l, 9-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

7-ethoxy-2, 9-diethyl-l-methyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

9-benzyl-7-ethoxy-2-ethyl-l-methyl-4 , 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

7-ethoxy-l, 2-dimethyl-4, 9-dihydro-3H-pyrido [3, 4-i>] indol-2- ium, 7-ethoxy-l, 2, 9-trimethyl-4, 9-dihydro-3H-pyrido [3, 4-jb] indol-2- ium, 7-ethoxy-9-ethyl-l, 2-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

9-benzyl-7-ethoxy-l , 2-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium, 2-ethyl-7-methoxy-l-methyl-4 , 9-dihydro-3H-pyrido [3, 4- b] indole-2-ium

2-ethyl-7-methoxy-l , 9-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

2, 9-diethyl-7-methoxy-l-methyl-4 , 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

9-benzyl-2-ethyl-7-methoxy-l-methyl-4 , 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium,

1, 2-dimethyl-7- (pentyloxy) -4, 9-dihydro-3H-pyrido [3, 4-b] indol- 2-ium, 1,2, 9-trimethyl-7- (pentyloxy) -4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

9-ethyl-l, 2-dimethyl-7- (pentyloxy) -4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

9-benzyl-l, 2-dimethyl-7- (pentyloxy) -4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium,

2-ethyl-l-methyl-7- (pentyloxy) -4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

2-ethyl-l, 9-dimethyl-7- (pentyloxy) -4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium, 2, 9-diethyl-l-methyl-7- (pentyloxy) -4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

9-benzyl-2-ethyl-l-methyl-7- (pentyloxy) -4, 9-dihydro-3H- pyrido [3, 4-i>] indol-2-ium,

2-benzyl-l-methyl-7- (pentyloxy) -4, 9-dihydro-3H-pyrido [3, 4- jb] indol-2-ium,

2-benzyl-l, 9-dimethyl-7- (pentyloxy) -4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium,

2-benzyl-9-ethyl-l-methyl-7- (pentyloxy) -4, 9-dihydro-3H- pyrido [3, 4-i>] indol-2-ium, 2, 9-dibenzyl-l-methyl-7- (pentyloxy) -4, 9-dihydro-3H- pyrido [3, 4-i>] indol-2-ium, 7-methoxy-l, 2-dimethyl-4, 9-dihydro-3H-pyrido [3, 4-£>] indol-2- ium,

7-methoxy-l, 2, 9-trimethyl-4, 9-dihydro-3H-pyrido [3, 4-£>] indol-

2-ium, 9-ethyl-7-methoxy-l , 2-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

9-benzyl-7-methoxy-l , 2-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-2-ium,

9- (4-carboxybenzyl) -7-methoxy-l-methyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium,

9- (4-carboxybenzyl) -7-methoxy-l, 2-dimethyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium,

9- (4-carboxybenzyl) -2-ethyl-7-methoxy-l-methyl-4, 9-dihydro-

3H-pyrido [3, 4-£>] indol-2-ium, 2-benzyl-9- (4-carboxybenzyl) -7-methoxy-l-methyl-4, 9-dihydro-

3H-pyrido [3, 4-i>] indol-2-ium,

9- (3-carboxybenzyl) -7-methoxy-l-methyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium,

9- (3-carboxybenzyl) -7-methoxy-l, 2-dimethyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indol-2-ium,

9- (3-carboxybenzyl) -2-ethyl-7-methoxy-l-methyl-4, 9-dihydro-

3H-pyrido [ 3 , 4 -i>] indol -2 - ium, or

2-benzyl-9- (3-carboxybenzyl) -7-methoxy-l-methyl-4, 9-dihydro-

3H-pyrido [ 3 , 4 -i>] indol -2 - ium .

Embodiments of the invention are described in the following.

Fig. 1 shows a Michaelis-Menten kinetic of the 0- dealkylation of a first compound according to the invention as substrate by CYP3A4,

Fig. 2 shows the catalytic activity of different CYP enzymes with a first compound Ia according to the in- vention as substrate, Fig. 3 shows the inhibition of the CYP3A4 catalyzed reaction of a first compound according to the invention by ketoconazole,

Fig. 4 shows the catalytic activity of different CYP enzymes with a first compound Ic according to the invention as substrate,

Fig. 5 shows the catalytic activity of different CYP en- zymes with a first compound 2a according to the invention as substrate, and

Fig. 6 shows HPLC/UV chromatograms (320nm) of incubation samples of substance Ib with human liver microsomes and uridin-5' -diphosphate-glucuronic acid before

(panel A) and after (panel B) the use of β- glucuronidase .

Synthesis

Substances of the basic structure 3 such as 1 -methyl- 9H- pyrido [ 3, 4-£>] indole-7-ol and 7-methoxy-l-methyl-9H- pyrido [ 3, 4-jb] indole or 4 such as l-methyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indole-7-ol and 7-methoxy-l-methyl-4, 9-dihydro- 3H-pyrido [3, 4-£>] indole or the salts of these substances are reacted with an alkylating reagent or benzylation reagent such as benzyl bromide, 4-bromomethylbenzoic acid and a base such as potassium carbonate or potassium hydroxide in an ap- propriate solvent such as tetrahydrofuran, acetone, dimethyl sulfoxide, acetonitrile, or dimethyl formamide at a temperature ranging from 0 to 80 ⁰ C. Reaction products are single and multiple alkylated products according to formula 1 and 2 such as 2-benzyl-7-benzyloxy-l-methyl-9H-pyrido [3, 4-£>] indole- 2-ium which are suitable as substrates for enzymes, e.g., drug metabolizing enzymes such as CYP enzymes.

Synthesis of a first compound according to formula 1:

If l-methyl-9H-pyrido [3, 4-£>] indole-7-ol according to formula 5 is used with benzyl bromide as benzylation reagent and potassium carbonate as base substance Ia results as reaction product and substance Ib as by-product. Substance Ib is also the product of the enzymatic reaction of the substance Ia. The synthesis is performed as follows:

1 b

500 mg (2.5 mmol) of l-methyl-9H-pyrido [3, 4-£>] indole-7-ol 5 were dissolved in 25 ml dimethyl formamide (DMF) . 690 mg potassium carbonate (5 mmol) and 0.4 g (2.5 mmol) benzyl bromide 6 were added. After 24 hours of stirring at room temperature the reaction mixture was centrifugated at 3000 g for 10 minutes. The supernatant was collected and 5 ml water were added. Afterwards it was chromatographed on a reversed phase silica gel using acetonitrile, water and 0.05 % trifluoroa- cetic acid. In this way substances Ia and Ib could be separated. After evaporation of the solvent substances Ia and Ib remained as white powders. Substances Ia and Ib were identi- fied as 2-benzyl-7-benzyloxy-l-methyl-9H-pyrido [3, 4-b] indol- 2-ium trifluoroacetate salt Ia and 2-benzyl-7-hydroxy-l- methyl-9H-pyrido [3, 4-b] indole-2-ium trifluoroacetate salt Ib. The counterions are not shown in the above reaction scheme. The yield of substance Ia as trifluoroacetate salt was 295 mg which corresponds to 0.60 mmol and 24 %. The yield of substance Ib was 141 mg which corresponds to 0.35 mmol and 14 %.

Substance Ia can also be synthesized in a two step procedure as follows:

1. Synthesis of the 2-benzyl-7-hydroxy-l-methyl-9H- pyrido [3, 4-b] indole-2-ium salt Ib

1b

500 mg (2.5 mmol) of l-methyl-9H-pyrido [3, 4-£>] indole-7-ol 5 were dissolved in 250 ml tetrahydrofuran (THF) . 0.4 g

(2.5 mmol) benzyl bromide 6 were added. After 24 hours of stirring at 50 ⁰ C the reaction mixture was stored at 4 ⁰ C for 12 hours. Afterwards the precipitate was washed with THF and dissolved in acetonitrile . Afterwards it was chromatographed on a reversed phase 18-silica gel using acetonitrile, water and 0.05 % trifluoroacetic acid. In this way substance Ib could be separated. After evaporation of the solvent substance Ib remained as white powder which was identified as 2- benzyl-7-hydroxy-l-methyl-9H-pyrido [3, 4-b] indole-2-ium trif- luoroacetate salt. The counterion is not shown in the above reaction scheme. The yield of substance Ib as trifluoroace- tate salt was 895 mg which corresponds to 2.23 mmol and 89 %. Substance Ib can be used as a reference substance for the metabolite of substance Ia.

2. Synthesis of the 2-benzyl-7-benzyloxy-l-methyl-9H- pyrido [3, 4-£>] indole-2-ium salt Ia

DMSO/ACN

1b 1a

500 mg (1.25 mmol) of the 2-benzyl-7-hydroxy-l-methyl-9H- pyrido [3, 4-b] indole-2-ium trifluoroacetate salt Ib were dissolved in 25 ml of a mixture of 4 parts acetonitrile (ACN) and one part dimethyl sulfoxide (DMSO) . 690 mg potassium carbonate (5 mmol) and 0,4 g (2.5 mmol) benzyl bromide were added. After 12 hours of stirring at room temperature the reac- tion mixture was centrifugated at 3000 g for 10 minutes. The supernatant was collected and 5 ml water were added. Afterwards it was chromatographed on a reversed phase silica gel using acetonitrile, water and 0.05 % trifluoroacetic acid. In this way substance Ia could be separated. After evaporation of the solvent substance Ia remained as white powder. Substance Ia was identified as 2-benzyl-7-benzyloxy-l-methyl-9H- pyrido [3, 4-b] indole-2-ium trifluoroacetate salt. The counte- rion is not shown in the above reaction scheme. The yield of substance Ia as trifluoroacetate salt was 133 mg which cor- responds to 0.27 mmol and 22 %. Substance Ia can be used as substrate for CYP3A4, CYPlBl and CYP2D6.

Synthesis of a further first compound according to formula 1: 1 . Synthes i s of the 9- ( 4 -carboxy-benzyl ) - 7 -methoxy- l -methyl - 9H-pyrido [ 3 , 4 -£>] indole-2 - ium salt Ic

100 mg (0.25 mmol) of 7-methoxy-l-methyl-9H-pyrido [3, 4- b] indole 7 were dissolved in 15 ml dimethyl sulfoxide (DMSO) . 1.0 g powdered sodium hydroxide (1.8 mmol) and 1.0 g (0.5 mmol) 4-bromomethylbenzoic acid 8 were added. After 1 hour of stirring at room temperature the reaction mixture was centri- fugated at 3000 g for 10 minutes. The supernatant was collected and 5 ml water were added. Afterwards it was chromato- graphed on a reversed phase 18-silica gel using acetonitrile, water and 0.05 % trifluoroacetic acid. In this way substance Ic could be separated. After evaporation of the solvent substance Ic remained as white powder which was identified as 9- (4-carboxy-benzyl) -7 -methoxy-1 -methyl- 9H-pyrido [3, 4-£>] indole- 2-ium trifluoroacetate salt. The counterion is not shown in the above reaction scheme. The yield of substance Ic as trif- luoroacetate salt was 19.0 mg which corresponds to 0.04 mmol and 18 %. Substance Ic can be used as substrate for CYP2C8, CYP2C9 and CYP2C19.

2. Synthesis of the 9- (4-carboxy-benzyl) -7-hydroxy-l-methyl- 9H-pyrido [3, 4-£>] indole-2-ium salt Id

25 mg (0.05 mmol) of the 9- (4-carboxy-benzyl) -7-methoxy-l- methyl-9H-pyrido [3, 4-£>] indole-2-ium trifluoroacetate salt Ic were dissolved in 10 ml concentrated hydrobromic acid (HBr) solution (48 %) and 10 ml water. After refluxing for 12 hours the reaction mixture was neutralized to pH 7 with concentrated sodium hydroxide solution. Afterwards it was chromato- graphed on a reversed phase silica gel using acetonitrile, water and 0.05 % trifluoroacetic acid. In this way substance Id could be separated. After evaporation of the solvent substance Id remained as white powder. Substance Id was identified as 9- (4-carboxy-benzyl) -7-hydroxy-l-methyl-9H- pyrido [3, 4-b] indole-2-ium trifluoroacetate salt. The counte- rion is not shown in the above reaction scheme. The yield of substance Id as trifluoroacetate salt was 9.2 mg which corresponds to 0.02 mmol and 43 %. Substance Id can be used as a reference substance for the metabolite of substance Ic.

Synthesis of a first compound according to formula 2:

1. Synthesis of the 7-methoxy-l, 2-dimethyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indole-2-ium salt 2a

2a 50 mg (0.23 mmol) of 7-methoxy-l-methyl-4, 9-dihydro-3H- pyrido [3, 4-£>] indole 9 were dissolved in 5 ml dimethyl sulfoxide (DMSO) and 70 mg (1 mmol) methyliodide were added. After 12 hours of stirring at 45°C trifluoroacetic acid (1 ml) was added to the reaction mixture. Afterwards the precipitate was washed with THF and dissolved in acetonitrile . Afterwards it was chromatographed on a reversed phase C18-silica gel using acetonitrile, water and 0.05 % trifluoroacetic acid. In this way substance 2a could be separated. After evaporation of the solvent substance 2a remained as yellowish powder which was identified as 7-methoxy-l, 2-dimethyl-4, 9-dihydro-3H- pyrido [3, 4-b] indole-2-ium trifluoroacetate salt. The counte- rion is not shown in the above reaction scheme. The yield of substance 2a as trifluoroacetate salt was 47.9 mg which corresponds to 0.14 mmol and 62 %. Substance 2a can be used as substrate for CYP2D6.

2. Synthesis of the 7 -hydroxy- 1, 2-dimethyl-4, 9-dihydro-3H- pyrido [3, 4-b] indole-2-ium salt 2b

10 2b

50 mg (0.25 mmol) of l-methyl-4, 9-dihydro-3H-pyrido [3, 4- b] indol-7-ol 10 were dissolved in 2 ml dimethyl sulfoxide (DMSO) . After 16 hours of stirring at 45°C tetrahydrofuran (4 ml) was added to the reaction mixture. Afterwards the precipitate was washed with THF and dissolved in acetonitrile. Afterwards it was chromatographed on a reversed phase silica gel using acetonitrile, water and 0.05 % trifluoroacetic ac- id. In this way substance 2b could be separated. After evaporation of the solvent substance 2b remained as yellowish powder. Substance 2b was identified as 7-hydroxy-l, 2- dimethyl-4, 9-dihydro-3H-pyrido [3, 4-£>] indole-2-ium trifluoroa- cetate salt. The counterion is not shown in the above reaction scheme. The yield of substance 2b as trifluoroacetate salt was 12.4 mg which corresponds to 0.06 mmol and 23 %. Substance 2b can be used as a reference substance for the metabolite of substance 2a.

Enzyme Assays

The Michaelis-Menten constant (K _m ) and the maximal reaction velocity (V _max ) are important parameters for inhibition as- says. To determine the inhibitory activity of test compounds the substrate concentration in the assay should be about the K _m value. For the determination of K _m and V _max of the following CYP3A4-catalyzed O-dealkylation reaction of substance Ia

1a 1b

different concentrations (0.1, 0,5, 1, 2.5, 5, 10, 25, 50, 75, 100 μM) of substance Ia were contacted with 5 pmol/ml of recombinant human CYP3A4 (Supersomes ^® , BD Biosciences, 2350 Qume Drive, San Jose, CA USA 95131) and 2 mM NADPH as coenzyme in a 100 mM potassium phosphate buffer (pH 7.4; 3 mM MgCl ₂ ) . After incubation for 20 minutes at 37°C the reaction product Ib was quantified using mass spectrometry after liquid chromatography. From Fig. 1 it can be seen that the enzymatic reaction of substance Ia as substrate shows a Michaelis-Menten kinetic in the range from 0.1 to 10 μM whereas an inhibition by the substrate occurs at higher concentrations of the substrate. For the calculation of K _m and V _max the Sigma Plot 10.0 software with enzyme kinetic module (SPSS, Inc., Chicago, IL, USA) was used. For substance Ia the resulting K _m value is 1.6 μM and V _max is 7.7 pmol/min/pmol CYP3A4.

Having a K _m value of 1.6 μM substance Ia has an affinity for CYP3A4 that is much higher than that of the usually used fluorescence substrate 7-benzyloxy-4-trifluoromethylcumarin (BFC) and benzyloxyresorufin (BzRes) . This can be seen from the following comparison:

Substrate Metabolite K _m " max

[μM] [pmol/min/pmol CYP3A4]

1a 1 b 1.6 7.7

BFC ¹ 7-Hydroxy-4- >200 1.5 (at 40 μM BFC) trifluoromethylcoumarin

BzRes ¹ Resorufin 38 0.3

Midazolam ² 1 -Hydroxymidazolam 0.6 16.3

¹ according to US 6,207,404

² according to Walsky R. L., Obach R. S., 2004, Drug Metab Dispos 32: 647-660

Whereas BFC and BzRes are used in inhibition assays at a concentration of 50 μM substance Ia can be used in inhibition assays at a 25 fold lower substrate concentration such that no solubility problems occur. Furthermore, reaction velocity of substance Ia is about 5-fold higher than that of BFC. The low K _m value of substance Ia and its high reaction velocity characterize this substance as an ideal substrate for CYP3A4.

To determine the catalytic activity of CYP3A4 for the reac- tion with substance Ia 2 μM of this substance, a concentration that corresponds to the K _m value, were contacted with 5 pmol/ml recombinant human CPY3A4 (Supersomes ^® , BD Bios- ciences) and 2 mM NADPH in 100 mM potassium phosphate buffer (pH 7.4; 3 mM MgCl ₂ ) . After incubation for 20 minutes at 37°C the metabolite Ib was quantified using liquid chromatography followed by mass spectrometry. For this reaction 4.5 pmol/min/pmol CYP3A4 could be determined as activity of the enzyme. According to US 6,207,404 the activity of CYP3A4 for the reaction of BFC at a concentration of 50 μM is about 1.5 pmol/min/pmol CYP3A4. This shows that the activity of the enzyme for the reaction of substance Ia is 3-fold higher than that for the reaction of BFC.

For the determination of the catalytic activity of other CYP- enzymes with respect to the reaction of substance Ia 2 μM of substance Ia were contacted with 15 pmol/ml CYP enzyme (Supersomes ^® , BD Biosciences) and 2 mM NADPH in 100 mM potassium phosphate buffer (pH 7.4; 3 mM MgCl ₂ ) with the exception of CYP3A4 that was used at a concentration of 5 pmol/ml. As can be seen from Fig. 2 the reaction of substrate Ia to reaction product Ib could be catalyzed by CYP3A4, CYPlBl and CYP2D6.

For the determination of the IC ₅₀ value of the CYP3A4- inhibitor ketoconazole this inhibitor was used in concentra- tions of 0.00025-10 μM with 2 μM substance Ia, 5 pmol/ml recombinant human CYP3A4 (Supersomes ^® , BD Biosciences) and 2 mM NADPH in 100 mM potassium phosphate buffer (pH 7.4; 3 mM MgCl ₂ ) . After incubation for 20 minutes at 37°C the metabolite Ib was quantified using liquid chromatography and mass spectrometry. For the calculation of the IC ₅₀ value the Sigma Plot 10.0 software with enzyme kinetic module was used.

The result of the inhibition can be seen in Fig. 3. The cal- culated IC ₅₀ value is 24.9 ± 1.3 nM. This corresponds to the values that had been determined for CYP3A4 using BFC and midazolam as substrate.

For the determination of K _m and V _max of the following CYP2C- catalyzed O-demethylation reaction of substance Ic

different concentrations (0.25, 0,5, 1, 2.5, 5, 10, 25, 50, 75, 100 μM) of substance Ic were contacted with 5 pmol/ml of recombinant human CYP2C8, CYP2C9 or CYP2C19 (Supersomes ^® , BD Biosciences, 2350 Qume Drive, San Jose, CA USA 95131) and 2 mM NADPH as coenzyme in a 100 mM potassium phosphate buffer (pH 7.4; 3 mM MgCl ₂ ) . After incubation for 30 minutes at 37°C the reaction product Id was quantified using mass spectrometry after liquid chromatography.

The enzymatic reactions of substance Ic as substrate for CYP2C8, CYP2C9 and CYP2C19 show Michaelis-Menten kinetics in the range from 0.25 to 100 μM. For the calculation of K _m and V _max the Sigma Plot 10.0 software with enzyme kinetic module (SPSS, Inc., Chicago, IL, USA) was used. For substance Ic the resulting K _m and V _max values for CYP2C8, CYP2C9 and CYP2C19 are summarized in the following table: 1c K _m " max

[μM] [pmol/min/pmol CYP enzyme]

CYP2C8 7.3 1.2

CYP2C9 8.1 9.4

CYP2C19 23.2 22.4

For the determination of the catalytic activity of other CYP- enzymes with respect to the reaction of substance Ic 25 μM of substance Ic were contacted with 15 pmol/ml CYP enzyme (Supersomes ^® , BD Biosciences) and 2 mM NADPH in 100 mM potassium phosphate buffer (pH 7.4; 3 mM MgCl ₂ ) . As can be seen from Fig. 4 the reaction of substrate Ic to reaction product Id could be catalyzed only by CYP2C8, CYP2C9 and CYP2C19. This indicates that the reaction is selective for the CYP2C subfamily.

For the determination of K _m and V _max of the following CYP2D6- catalyzed O-demethylation reaction of substance 2a

2a 2b

different concentrations (0.25, 0,5, 1, 2.5, 5, 10, 25, 50, 75, 100 μM) of substance 2a were contacted with 5 pmol/ml of recombinant human CYP2D6 (Supersomes ^® , BD Biosciences, 2350 Qume Drive, San Jose, CA USA 95131) and 2 mM NADPH as coenzyme in a 100 mM potassium phosphate buffer (pH 7.4; 3 mM MgCl ₂ ) . After incubation for 30 minutes at 37°C the reaction product 2b was quantified using mass spectrometry after liq- uid chromatography.

The enzymatic reaction of substance 2a as substrate for CYP2D6 shows Michaelis-Menten kinetics in the range from 0.25 to 100 μM. For the calculation of K _m and V _max the Sigma Plot 10.0 software with enzyme kinetic module (SPSS, Inc., Chicago, IL, USA) was used. For substance 2a the resulting K _m and V _max values for CYP2D6 was 11.3 μM and 9.7 pmol/min/pmol CYP enzyme, respectively.

For the determination of the catalytic activity of other CYP- enzymes with respect to the reaction of substance 2a 15 μM of substance 2a were contacted with 15 pmol/ml CYP enzyme (Supersomes ^® , BD Biosciences) and 2 mM NADPH in 100 mM potassium phosphate buffer (pH 7.4; 3 mM MgCl ₂ ) . As can be seen from Fig. 5 the reaction of substrate 2a to reaction product 2b could be catalyzed only by CYP2D6. This indicates that the reaction is selective for CYP2D6.

The first compound according to formula 1, e.g., 2-benzyl-7- hydroxy-l-methyl-9H-pyrido [3, 4-£>] indole-2-ium salt, 7- hydroxy-1 , 2-dimethyl-9H-pyrido [ 3, 4-£>] indole-2-ium salt and 9- (4-carboxy-benzyl) -7-hydroxy-l-methyl-9H-pyrido [3, 4-£>] indole- 2-ium salt, and according to formula 2, e.g., 2-benzyl-7- hydroxy-l-methyl-4, 9-dihydro-3H-pyrido [3, 4-£>] indole-2-ium salt or 7-hydroxy-l, 2-dimethyl-4, 9-dihydro-3H-pyrido [3, 4- b] indole-2-ium salt can also be used as substrate for glucu- ronosyltranferases (UGTs) . For example substances Ib and 2b are catalyzed to the O-glucoronides by UGTs from human liver microsomes according to the following reaction scheme:

1b 1b-O-glucuronide

2b 2b-O-glucuronide

For the determination of the catalytic activity of glucurono- syltranferases with respect to the reaction of substances Ib and 2b 100 μM of substances Ib and substance 2b were contacted with 1 mg/ml human liver microsomes (BD Biosciences, 2350 Qume Drive, San Jose, CA USA 95131) and 50 μg/ml alame- thicin in a 100 mM potassium phosphate buffer (pH 7.4; 6 mM MgCl ₂ ) for 15 minutes at 0 ⁰ C each. Afterwards 2 mM UDPGA (uridin-5' -diphosphate-glucuronic acid) as coenzyme was added to each of the reaction mixtures. The reaction mixtures were incubated for 60 minutes at 37°C. The reaction products were identified as the O-glucuronides of substances Ib and 2b by mass spectrometry and by the cleavage of the O-glucuronides using β-glucuronidase of Helix pomatia. Fig. 6 shows HPLC/UV chromatograms (320nm) of incubation samples of substance Ib with human liver microsomes and uridin-5' -diphosphate- glucuronic acid before (panel A) and after the use of β- glucuronidase (panel B) . The peak marked with "lb-Gluc" in panel A was caused by the lb-O-glucuronide that was converted in substance Ib by β-glucuronidase . Therefore, a corresponding peak is absent in panel B.