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7‐Substituted 7‐Deaza‐2′‐deoxyadenosines and 8‐Aza‐7‐deaza‐2′‐deoxyadenosines: Fluorescence of DNA‐Base Analogues Induced by the 7‐Alkynyl Side Chain
Author(s) -
Seela Frank,
Zulauf Matthias,
Sauer Markus,
Deimel Michael
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(20000510)83:5<910::aid-hlca910>3.0.co;2-4
Subject(s) - chemistry , fluorescence , deoxyribonucleosides , amine gas treating , alkyl , base (topology) , photochemistry , stereochemistry , combinatorial chemistry , dna , organic chemistry , mathematical analysis , biochemistry , physics , mathematics , quantum mechanics
7‐Alkynylated 7‐deazaadenine (pyrrolo[2,3‐ d ]pyrimidin‐4‐amine) 2′‐deoxyribonucleosides show strong fluorescence which is induced by the 7‐alkynyl side chain ( Table 3 ). A large Stokes shift with an emission around 400 nm is observed when the compound is irradiated at 280 nm. The solvent dependence indicates the formation of a charged transition state. The fluorescence appears when the triple bond is in conjugation with the heterocyclic base. Electron‐donating substituents at the triple bond increase the fluorescence, while electron‐withdrawing residues reduce it. In comparison, the 7‐alkynylated 8‐aza‐7‐deazaadenine (pyrazolo[3,4‐ d ]pyrimidin‐4‐amine) 2′‐deoxyribonucleosides are rather weakly fluorescent ( Table 4 ). Quantum yields and fluorescence decay times are measured. The synthesis of the 7‐alkynylated 7‐deaza‐2′‐deoxyadenosines and 8‐aza‐7‐deaza‐2′‐deoxyadenosines was performed with 7‐deaza‐2′‐deoxy‐7‐iodoadenosine ( 6 ) or 8‐aza‐7‐deaza‐2′‐deoxy‐7‐iodoadenosine ( 22 ) as starting materials and employing the Pd 0 ‐catalyzed cross‐coupling reaction with the corresponding alkynes ( Schemes 1 , 4 , and 5 ). Catalytic hydrogenation of the side chain of the unsaturated nucleosides 5 and 17 afforded the 7‐alkyl derivatives 18 and 19 , respectively, which do not show significant fluorescence ( Scheme 2 ).