- Photophysical and Photochemical Properties of 3-methylpterin as a New and More Stable Pterin-type Photosensitizer
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Pterin derivatives are heterocyclic compounds which are present in different biological systems. Neutral aqueous solutions of pterins present acid–base and keto–enol equilibria. These compounds, under UV-A radiation fluoresce, undergo photooxidation, generate reactive oxygen species and photoinduce the oxidation of biological substrates. As photosensitizers, they may act through different mechanisms, mainly through an electron transfer-initiated process (type-I mechanism), but they also produce singlet molecular oxygen (1O2) upon irradiation (type-II mechanism). In general, upon UV-A excitation two triplet states, corresponding to the lactim and lactam tautomers, are formed, but only the last one is the responsible for the photosensitized reactions of biomolecules. We present a study of the photochemical properties of 3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, exists only in the lactam form. Also an improvement in the synthesis of 3-Mep is reported. The spectroscopic properties 3-Mep in aqueous solution were similar to those of the unsubstituted pterin derivative (Ptr) in its acid form, such as absorption, fluorescent and phosphorescent emission spectra. Experiments using 2′-deoxyguanosine 5′-monophosphate (dGMP) as oxidizable target demonstrated that methylation at C-3 position of the pterin moiety does not affect significantly the efficiency of photosensitization, but results in a more photostable sensitizer.
- Estébanez, Sandra,Lorente, Carolina,Kaufman, Teodoro S.,Larghi, Enrique L.,Thomas, Andrés H.,Serrano, Mariana P.
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- Pteridines. Part CXIII. Protection of Pteridines
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The low solubulity of pterins can drastically be improved by N2-acylation or formation of the N2-[(dimethylamino)methylene] derivatives. Both types of compounds can be alkylated under Mitsunobu conditions to form from N2-acylpterins (see 2 and 3) and their derivatives (see 5, 6, 8, 9, 11, 13, 15, and 17) selectively the O4-alkyl derivatives 22-31, whereas the electron-donating [(dimethylamino)methyleneamino] function in 46-51 gives, in a selective reaction, the N(3)-substitution (->52-61). N2,N2-Dimethylpterins and 18 and 19 and N2-methylpterins 20 and 21 direct alkylation also to the O4-position (->32-35, 38 and 39). Deacylation can be achieved under very mild conditions by solvolysis with MeOH (22->40, 26->41), and displacement of the O4-[2-(4-nitrophenyl)ethyl] group proceeds with ammonia at room temperature to the corresponding pteridin-2,4-diamine 42-45. Cleavage of the N2-[(dimethylamino)methylene] group works well with ammonia (->62-67). The advantage of applying the 2-(4-nitrophenyl)ethyl (npe) group as blocking group is seen in its selective removal by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) under aprotic conditions without harming the other substituents.
- Yao, Qizheng,Pfleiderer, Wolfgang
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