n-Propyldiazonium ion alkylates O6 of guanine with rearrangement, but alkylates N-7 without rearrangement.

Treatment of guanosine with n-propylnitrosourea yields 7-n-propylguanine (after acid hydrolysis) but O6-isopropylguanosine. Similarly, injection of [3H]di-n-propylnitrosamine into Sprague--Dawley rats resulted in isolation of 7-n-propylguanine from RNA, but O6-isopropylguanosine. The amounts of the different adducts indicate that attack at both N-7 and O6 of guanine proceed by bimolecular substitution (otherwise significant levels of 7-isopropylguanine should have been seen), but the observed rearrangement indicates that the transition state for reaction at O6 may be much looser than that for reaction at N-7.