Alkylation of pyrrole-2-carboxaldehyde (II) with 2-nitrobenzyl chloride (I) in the presence of NaH afforded the N-benzyl pyrrole (III). Subsequent reductive ring closure of (III) by hydrogenation over Pd/C produced the pyrrolobenzodiazepine (IV). Acid-catalyzed esterification of 6-aminonicotinic acid (V) with either methanol or ethanol provided the corresponding esters (VIa) or (VIb). Further coupling of (VIa) or (VIb) with two equivalents of 5-fluoro-2-methylbenzoyl chloride (VII) gave rise to imide (VIII). Simultaneous hydrolysis of ester function and one benzoyl group of (VIIIa-b) with NaOH furnished acid (IX), which was then converted to the corresponding acid chloride (X) employing either thionyl chloride or oxalyl chloride. Finally, coupling of acid chloride (X) with amine (IV) in the presence of Et3N yielded the target amide.
Title compound has been obtained by two synthetic procedures: 1) Pyrrole-2-carbaldehyde (I) was alkylated with 2-nitrobenzyl bromide (II) in the presence of NaH to afford the N-nitrobenzyl pyrrole (III). Then, reductive cyclization over Pd/C produced the pyrrolobenzodiazepine (IV). Subsequent condensation of (IV) with acid chloride (VI), prepared from 3-methoxy-4-nitrobenzoic acid (V) and oxalyl chloride, gave benzamide (VII). The nitro group of (VII) was then reduced by catalytic hydrogenation over Pd/C, and the resulting amine (VIII) was further acylated with biphenyl-2-carbonyl chloride (IX) in the presence of diisopropyl ethylamine (DIEA) to yield diamide (X). Finally, the Mannich reaction with tetramethyl diaminomethane and paraformaldehyde introduced the (dimethylamino)methyl group into the pyrrole nucleus. 2) In a related procedure, 3-methoxy-4-nitrobenzoic acid (V) was esterified with MeOH in the presence of SOCl2. The nitrobenzoic ester (XI) was reduced to aminoester (XII) by hydrogenation over Pd/C, and then acylated with biphenyl-2-carbonyl chloride (IX) and DIEA to produce amide (XIII). Subsequent saponification of the ester function of (XIII), followed by treatment with oxalyl chloride furnished acid chloride (XIV), which was then condensed with the tricyclic intermediate (IV) to yield diamide (X). Finally, the (dimethylamino)methyl group was introduced, as before, by means of a Mannich reaction.
The intermediate pyrrolobenzodiazepine (IV) was prepared by alkylation of pyrrole-2-carboxaldehyde (I) with 2-nitrobenzyl bromide (II), followed by reductive cyclization of the resulting nitro aldehyde (III).
Acid chloride (VI) prepared from 2-biphenylcarboxylic acid (V) and SOCl2 was coupled with methyl 4-amino-2-chlorobenzoate (VII) to yield amide (VIII). After hydrolysis of the ester group of (VIII) with NaOH, the resulting carboxylic acid (IX) was converted to acid chloride (X) using SOCl2. Finally, condensation of (X) with the tricyclic amine (IV) in the presence of DIEA furnished the title compound.