cyclopentenyl cytosine [ 1-(4-hydroxymethyl-2,3-dihydroxy-4-cyclopenten-1-yl)cytosine,1-cCyd,4-amino-1-(4,5-dihydroxy-3-(hydroxymethyl)-2-cyclopenten-1-yl)-2(1H)-pyrimidinone,CPE-c,CPE-cytosine,NSC 375575,NSC-375575,cCyd,cyclopentenyl cytosine, (1R-(1alpha,4beta,5alpha))-isomer,cyclopentenylcytosine ] inhibits CTP synthetase; used in therapy of colonic neoplasms; structure given in first source; RN given refers to the (1R-(1alpha,4beta,5beta))-isomer