The invention provides processes of preparing 3-substituted 1-(chloromethyl)- 1,2-dihydro-3H-[ring fused indol-5-yl(amine-derived)] compounds of formula (I) and its analogues, or a physiologically functional derivative thereof, (I), wherein A and B together may represent a fused optionally substituted benezene, naphthalene, pyridine, furan or a pyrrole ring, where the optional substituents are represented by Y; X is halogen or OSO.sub.2R, and W is selected from NO.sub.2, NHOH, N(R.sup.3).sub.2NHR.sup.3, NHCO.sub.2R.sup.3, N(phthaloyl) or NH.sub.2, or W is further selected from the group (a), wherein J is selected from OH or H, and P is a group which is a substrate suitable for a nitroreductase or carboxypeptidase enzyme. The invention is also directed to the use of compounds of formula (I) prepared by the processes of the invention as cytotoxins for cancer therapy and as prodrugs for gene-directed enzyme-prodrug therapy (GDEPT) and antibody-directed enzyme-prodrug theraphy (ADEPT).