Reaction of 1-n-propyl-1-nitrosourea with DNA in vitro.

[n-propyl-2,3-3H]1-n-Propyl-1-nitrosourea (PNU) (sp. act.: 665 mCi/mmol) was synthesized and incubated with calf thymus DNA at pH 7.0 and 37 degrees C in vitro. The degree of alkylation was proportional to the concentration of PNU added. The extent was 68 pmol/mg of DNA at 1 mM PNU. After mild acid hydrolysis, purine bases were separated by Sephadex G-10 column chromatography. Although O6-n-propylguanine and O6-iso-propylguanine were separated by this method, 7-n-propylguanine and 7-iso-propylguanine were not separated. Then we used a h.p.l.c. equipped with a mu Bondapak-C18 reverse phase column with a linear gradient elution. 7-n-Propylguanine and O6-n-propylguanine were identified as major reaction products, and 7-iso-propylguanine and O6-iso-propylguanine were identified as minor reaction products. The ratio of O6-n- and iso-propylguanine/7-n- and iso-propylguanines was 0.73. This ratio is similar to that produced by 1-ethyl-1-nitrosourea and 1-n-butyl-1-nitrosourea.