5-Amino-1-(chloromethyl)-1,2-dihydro-3H-benz[e]indoles: Relationships between Structure and Cytotoxicity for Analogues Bearing Different DNA Minor Groove Binding Subunits

Abstract
A series of 5-amino-seco-CBI compounds, designed for use as effectors for prodrugs, were prepared to study structure−activity relationships for the cytotoxicity of side chain analogues. Compounds were prepared by coupling 1-(chloromethyl)-5-nitro-1,2-dihydro-3H-benz[e]indole to appropriate carboxylic acids, followed by nitro group reduction, or by coupling suitable 5-amino-protected indolines to α,β-unsaturated acids, followed by deblocking. These AT-specific DNA alkylating agents were evaluated for cytotoxicity in a series of tumor cell lines (AA8, UV4, EMT6, SKOV3). For those analogues bearing an indolecarbonyl side chain, the 5‘-methoxy derivative was the most cytotoxic (IC50 1.3 nM in AA8 cells, 4 h exposure), comparable to that of the parent CBI-TMI (5‘,6‘,7‘-trimethoxyindole) derivative (IC50 0.46 nM in the above assay). A subset of solubilized derivatives bearing O(CH2)2NMe2 substituents were about 10-fold less potent. For compounds containing an acryloyl linker in the side chain, the 4‘-methoxycinnamoyl derivative proved the most cytotoxic (IC50 0.09 nM in the above assay). A number of these 5-amino-seco-CBI-TMI analogues (including the solubilized compounds) are of interest both as cytotoxins and as components of amine-based prodrugs designed for tumor-specific activation.

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