PHOTOCHEMICAL REACTIONS OF CYTOSINE AND 5‐METHYLCYTOSINE WITH METHYLAMINE AND n‐BUTYLAMINE

Abstract

The photoinduced exchange reactions of cytosine (la) and 5‐methylcytosine (IIa) with two primary amines have been studied. The reactions of Ia and IIa with methylamine lead, respectively, to 1‐methylcytosine (Ib) and 1,5‐dimethylcytosine (IIb) as final products; the reactions of the same two starting materials with n‐butylamine gives the corresponding n‐butyl compounds. The reactions of IIa with the two amines also gave small amounts of 1‐methylthymine and 1‐n‐butylthymine. An opened ring intermediate, N‐(N'‐methylcarbamoyl)‐3‐arnino‐2‐methylacrylamidine (IVa), was isolated from the IIa‐methylamine system irradiated at pH 7 and shown to be a precursor of both IIb and 1‐methylthymine. The pH profiles for rate of production of IIb, 1‐methylthymine and IVa in the reaction of IIa with methylamine were determined and found to be similar in shape. All three profiles show a maximum in reactivity at about pH 8.7 with some reactivity being detectable at pH values as low as 5.

Opened‐Ring Adducts of 5‐Methylcytosine and 1,5‐Dimethylcytosine with Amines and Water and Evidence for an Opened‐Ring Hydrate of 2′‐Deoxycytidine

“…The presence of a doublet, in the signal corresponding to the CONHC H 3 protons, provides confirmation that these protons are incorporated into the amide group. The chemical shift values of the nonexchangeable protons given in Table 1 for IVb are near the values of those found previously (23) where the NMR of this compound was run in D 2 O.…”

“…The protocols for its preparation, isolation and purification are given in Appendix S1 (It should be noted that the overall protocol given in Appendix S1 is a modified and improved version of that given in [23]. ) Consistent with, but differing very slightly from previously reported data (23), the UV spectrum of P B in distilled water showed λ max = 305 and 228 nm and λ min = 256 nm. The ESI mass spectrum of P B displayed peaks at 157.1 [M + H + ] and 179.1 [M + Na + ], indicating that this product contained both m5C and methylamine.…”

“…The opened‐ring conjugate, formed in the reaction between m5C and methylamine, has been previously isolated and characterized as having the structure IVb (23). The protocols for its preparation, isolation and purification are given in Appendix S1 (It should be noted that the overall protocol given in Appendix S1 is a modified and improved version of that given in [23]. ) Consistent with, but differing very slightly from previously reported data (23), the UV spectrum of P B in distilled water showed λ max = 305 and 228 nm and λ min = 256 nm.…”

“…Reaction of m5C with methylamine (MA) leads to N ‐( N ′‐methylcarbamoyl)‐3‐amino‐2‐methylacrylamidine ( IVb ) (23). Similarly, reaction with methanol leads to N ‐carbomethoxy‐3‐amino‐2‐methylacrylamidine (24).…”

“…Product preparation, isolation and purification in the m5C‐methylamine system and the DMC‐methylamine system. Since the protocols for the preparation, isolation and purification of the m5C‐MA adduct (previously shown to be IVb [23]) and the DMC‐MA adduct are similar to those given for the m5C‐NH 3 system, they are provided in Appendix S1, rather than in the body of this paper.…”