2-Aminopurine, a fluorescent analog of guanosine and adenosine, is a widely used fluorescence-decay-based probe of DNA structure. When 2-Aminopurine is inserted in anoligonucleotide, its fluorescence is highly quenched by stacking with the natural bases. 2-Aminopurine has been used to probe nucleic acid structure and dynamics[1][2].

2-Aminopurine (2AP) is not valuable as afluorescent label because its fluorescence is highly quenched by stacking with the natural bases, when it is inserted in anoligonucleotide. However, it is this very susceptibility to interbase quenching that makes 2AP an exquisitely sensitivefluorescent probe of nucleic acid structure[1]. 2-Aminopurine differs from adenine (6-aminopurine) only in the position of the exocyclic amine group, and yet its fluorescence intensity is one thousand times that of adenine[1].

References:
[1]. J M Jean, et al. 2-Aminopurine fluorescence quenching and lifetimes: role of base stacking. Proc Natl Acad Sci U S A. 2001 Jan 2;98(1):37-41.
[2]. Dehong Tan, et al. Decreased glycation and structural protection properties of γ-glutamyl-S-allyl-cysteine peptide isolated from fresh garlic scales (Allium sativum L.). Nat Prod Res. 2015;29(23):2219-22.