A method of producing 6-amino-cyclopenta[g]quinazolines, in enantiomerically enriched form, is provided. In particular, the method may be applicable to the synthesis of N-N-4-[N-((6S)-2-hydroxymethyl-4-oxo-3,4,7,8-tetrahydro-6H-cyclo-penta[g]quinazolin-6-yl)-N-(prop-2-ynyl)amino]benzoyl}-L-γ-glutamyl}-D-glutamic acid (ONX-0801).