2-Chloro-4-fluorobenzoic acid (I) was converted to acid chloride (II) upon treatment with oxalyl chloride and a catalytic amount of DMF. Subsequent coupling of (II) with pyrrolobenzodiazepine (III) yielded the corresponding amide (IV). Then, displacement of the fluorine atom of (IV) by the sodium salt of 3-methylpyrazole (V) produced a mixture of the required compound and its regioisomer (VI), which were separated by column chromatography.
Treatment of benzonitrile derivative (I) with 3-methylpyrazole (II) and NaH in DMF or KOtBu in THF yields a mixture of regioisomers from which compound (III) is obtained by recrystallization. Compound (III) is then converted into the corresponding benzamide (IV) by means of K2CO3 and H2O2 in DMSO. Hydrolysis of (IV) with aqueous H2SO4 and NaNO2 affords benzoic acid derivative (V), which is then condensed with benzodiazepine (VI) in the presence of DIEA by means of oxalyl chloride in CH2Cl2 and catalytic DMF. Alternatively (V) can be obtained by direct hydrolysis of (III) with NaOH in EtOH or by following this route: Condensation of methyl ester (VII) with 3-methyl pyrazole (II) by means of KH in DMF provides a mixture of regioisomers from which compound (VIII) is chromatographically separated and finally saponified by treatment with LiOH in THF or NaOH in acetonitrile.
Acylation of the pyrrolobenzodiazepine (I) with 2-chloro-4-fluorobenzoyl chloride (V) ?prepared from the acid (VI) and oxalyl chloride and catalytic DMF ?with H黱ig's base in dichloromethane gives the acylated pyrrolobenzodiazepine (VII). Treatment of (VII) with a solution of the sodium salt of 3-methylpyrazole (VIII) in DMF yields a 85:15 mixture of WAY-VNA-932 and its 5-methyl isomer (IX) which can be separated by column chromatography using an ethyl acetate/hexane mixture over silica gel.
Alternatively, treatment of 2-chloro-4-fluorobenzonitrile (X) with the potassium salt of 3-methylpyrazole (VIII) in THF produces an excellent yield of a 9:1 mixture of the 2-chloro-4-(3-methylpyrazol-1-yl)benzonitrile (XI) and 2-chloro-4-(5-methylpyrazol-1-yl)benzonitrile (XII) which can be separated by fractional crystallization. Hydrolysis of the nitrile (XI) to the acid, activation as the acid chloride and acylation of the pyrrolobenzodiazepine using H黱ig's base in dichloromethane yields WAY-VNA-932 which is isolated by direct crystallization.
The reductocyclization of 1-(2-nitrobenzyl)pyrrole-2-carbaldehyde (I) gives the pyrrolobenzodiazepine (II), which is acylated with 2-chloro-4-nitrobenzoyl chloride (III) giving the expected 10-benzoyl derivative (IV). The reduction of the nitro group of (IV) with H2 over Pd/C or with SnCl2 yields the corresponding 4-amino derivative (V), which is finally acylated with 5-fluoro-2-methylbenzoyl chloride.
The acylation of 4-amino-2-chlorobenzoic acid methyl ester (VII) with 5-fluoro-2-methylbenzoyl chloride (VI) gives the corresponding amide (VIII), which is hydrolyzed at the ester group yielding the corresponding free acid (IX). The reaction of (IX) with SOCl2 affords the acyl chloride (X), which is finally condensed with the pyrrolobenzodiazepine (II) (obtained by the reductocyclization of 1-(2-nitrobenzyl)pyrrole-2-carbaldehyde (I)) to provide the target compound.
The pyrrolobenzodiazepine (I) is prepared in two steps. The sodium salt of pyrrole-2-carboxaldehyde (II) is prepared in DMF using NaH. Alkylation with 2-nitrobenzyl bromide (III) proceeds in excellent yield. Reduction with hydrogen over Raney nickel effects reduction of the nitro group to the amine which cyclizes in situ to the seven-membered imine that is reduced to the pyrrolobenzodiazepine in excellent yield in one pot.