Ring opening photoreactions of cytosine and uracil with ethylamine

C5-Morpholinomethylation of N1-sulfonylcytosines by a one-pot microwave assisted Mannich reaction

A fast and efficient route for the introduction of a morpholinomethyl moiety in the C5 position of the sulfonylated cytosine nucleobase has been developed.

Photohydrate-mediated reactions of uridine, 2'-deoxyuridine and 2'-deoxycytidine with amines at near neutral pH

Photohydrates are formed in high yield when uridine (Urd), 2'-deoxyuridine (dUrd), cytidine (Cyd) and 2'-deoxycytidine (dCyd) are irradiated with UVC in aqueous solution. The thermal reactions of the photohydrates of Urd with amines at pH values near pH 7.5 have been studied using UV spectroscopy, HPLC, mass spectrometry and, in some cases, NMR. It has been found that a number of amines (i.e. ethylenediamine, N,N'-dimethylethylenediamine, glycine, glycinamide, glycylglycine, glycylgylcylglycine, putrescine, spermidine and spermine) react thermally with such hydrates to form products with UV spectra characteristic of opened ring uridine-amine adducts. In general, these products display a strong absorption peak with λmax in the range between 288 and 310 nm. Mass spectral studies of a number of the products indicate that they contain one molecule of parent nucleoside and one molecule of reactant amine. Upon standing in water these products revert to parent hydrate, while heating produces parent nucleoside. Less comprehensive studies indicate that photohydrates of dUrd and dCyd undergo analogous thermal reactions. Preliminary results suggest that UV-irradiated polyuridylic acid and polycytidylic acid undergo similar reactions. These results may have relevance for obtaining a complete understanding of the biological effects of producing Urd and dCyd photohydrates in a cellular environment.

Ring-opening photoreactions of 5-methylcytosine with 3-mercaptopropionic acid and other thiols

The photoproducts from reaction of thymine with cysteine, an amino acid containing a sulfhydryl group, have been studied in detail, whereas results of less extensive studies have been reported for the uracil-cysteine system. However, products arising from corresponding reactions of cytosine and related compounds with compounds containing a sulfhydryl group have not been similarly studied. We report here the results of our study of the photoreaction of 5-methylcytosine (5MeCyt), a minor base occurring in mammalian DNA, with 3-mercaptopropionic acid (3MP), a model compound for cysteine. We found that this reaction proceeds at pH 7 to yield N-(N'-(2'-carboxyethyl)thiocarbamoyl)-3-amino-2-methylacrylamidine (Ia) as a primary photoproduct. A secondary thermal product, identified as 3-(2'-carboxyethylthio)-2-methylacrylamidine (IIa), appears if photoreacted solution is allowed to stand for appreciable times prior to workup; this latter compound is formed via an intermediate product. Heating of purified Ia at 100°C or standing at lower temperatures produces 3-amino-2-methylacrylamidine (IId); similarly, irradiation of Ia with UVB light in aqueous solution converts it into IId. Results from exploratory studies suggest that 5MeCyt similarly reacts with other thiols (2-mercaptoethanol, 2-mercaptoacetic acid) to form analogs of Ia and IIa. Other preliminary results suggest that 5-methyl-2'-deoxycytidine and 1,5-dimethylcytosine photoreact with 3MP to form compounds similar to Ia.

The photochemistry of thymidylyl-(3'-5')-5-methyl-2'-deoxycytidine in aqueous solution

The photochemistry of the dinucleoside monophosphate thymidylyl-(3'-5')-5-methyl-2'-deoxycytidine (Tpm5dC) has been studied in aqueous solution using both 254 nm and UV-B radiation. A variety of dinucleotide photoproducts containing 5-methylcytosine (m5C) have been isolated and characterized. These include two cyclobutane dimers (CBD) (the cis-syn [c,s]and trans-syn forms), a (6-4) adduct and its related Dewar isomer, and two isomers of a product in which the m5C moiety was converted into an acrylamidine. Small amounts of thymidylyl-(3'-5')-thymidine (TpT) were also formed, presumably as a secondary photoreaction product. In addition, a photoproduct was characterized in which the m5C moiety was lost, thus generating 3'-thymidylic acid esterified with 2'-deoxyribose at the 5-hydroxyl on the sugar moiety. The c,s CBD of Tpm5dC readily undergoes deamination to form the corresponding CBD of TpT. The kinetics of this deamination process has been studied; the corresponding enthalpy and entropy of activation for the reaction have been evaluated at pH 7.4 as being, respectively, 73.4 kJ/mol and -103.5 J/K mol. Deamination was not observed for the other characterized photoproducts of Tpm5dC.