Difluoroacetic acid: an alternative acid in the detritylation reaction for the solid-phase synthesis of oligonucleotides.

Dichloroacetic acid or trichloroacetic acid are commonly used in the detritylation reaction of the automated solid-phase synthesis of oligonucleotides. Dichloroacetic acid, however, is often contaminated with trichloroacetaldehyde (chloral), leading to the formation of inseparable impurities in the final oligonucleotide product. In this work, three different sequences, namely T18, d(TAA)6, and an 18-mer mixed sequence, were used as models to compare the deprotection efficiency of three acids: trichloroacetic acid, dichloroacetic acid, and difluoroacetic acid. Comparable purities of full-length products were obtained for the synthesis of the three model sequences when dichloroacetic acid or difluoroacetic acid were used during the detritylation reaction, however, conditions need to be optimized for the synthesis of purine-rich sequences. Therefore, difluoroacetic acid is a potential alternative to dichloroacetic acid in the solid-phase synthesis of oligonucleotides to avoid the impurity formation due to presence of chloral.

Anion exchange chromatography of oligonucleotides under denaturing conditions.

Denaturing anion exchange HPLC simplifies the chromatographic profiles of self-complementary sequences such as d(CG)6, d(CG)6 with locked nucleic acid modifications, d(AT)15, and polymerase chain reaction mixtures. These chromatographic conditions use eluents containing up to 4 M urea at pH 12.4, and lead to the abolishment of secondary structures and meaningful chromatographic patterns of self-complementary sequences. Similarly, PCR template, FAM-labelled primer and FAM-labelled PCR products were resolved, making interpretation of PCR reaction products possible.

Further investigation on the nitration of BODIPY with cupric nitrate: crystal structures of 4,4-di-fluoro-1,3,5,7,8-penta-methyl-2-nitro-4-bora-3a,4a-di-aza-s-indacene, 4,4-di-fluoro-3-nitro-8-phenyl-4-bora-3a,4a-di-aza-s-indacene, and 3-chloro-6-ethyl-5,7,8-trimethyl-2-nitro-4,4-diphenyl-4-bora-3a,4a-di-aza-s-indacene.

The treatment of non-fully substituted 4,4-di-fluoro-4-bora-3a,4a-di-aza-s-indacene (BODIPY) with cupric nitrate leads to the introduction of a nitro group at different positions of the BODIPY core, depending on the substitution pattern. This methodology complements the treatment of fully substituted BODIPY with cupric nitrate that was previously reported. The crystal structures of 4,4-di-fluoro-1,3,5,7,8-penta-methyl-2-nitro-4-bora-3a,4a-di-aza-s-indacene, C14H16BF2N3O2 (5a) 4,4-di-fluoro-3-nitro-8-phenyl-4-bora-3a,4a-di-aza-s-indacene, C15H10BF2N3O2(5b) and 3-chloro-6-ethyl-5,7,8-trimethyl-2-nitro-4,4-diphenyl-4-bora-3a,4a-di-aza-s-indacene, C26H25BClN3O2 (5d) are presented. In all three structures, the fused ring system is in a very flattened 'V-shape', with dihedral angles between the two outer five membered rings of 8.12 (14), 6.67 (9) and 12.30 (18) Šfor 5a, 5b and 5d, respectively. In each case, the central six-membered ring is in a flattened sofa conformation. In the crystal of 5a, mol-ecules are linked by weak C-H⋯O and C-H⋯F hydrogen bonds forming sheets parallel to (10-1). In the crystal of 5b mol-ecules are linked by weak C-H⋯O and C-H⋯F hydrogen bonds and π-π inter-actions forming sheets parallel to (001). In the crystal of 5d, weak C-H⋯O hydrogen bonds link mol-ecules into chains along [001]. In compound 5d, the atoms of the nitro group were refined as disordered over two sets of sites with occupancies 0.618 (12) and 0.382 (12).

Characterization of photophysical and base-mimicking properties of a novel fluorescent adenine analogue in DNA.

To increase the diversity of fluorescent base analogues with improved properties, we here present the straightforward click-chemistry-based synthesis of a novel fluorescent adenine-analogue triazole adenine (A(T)) and its photophysical characterization inside DNA. A(T) shows promising properties compared to the widely used adenine analogue 2-aminopurine. Quantum yields reach >20% and >5% in single- and double-stranded DNA, respectively, and show dependence on neighbouring bases. Moreover, A(T) shows only a minor destabilization of DNA duplexes, comparable to 2-aminopurine, and circular dichroism investigations suggest that A(T) only causes minimal structural perturbations to normal B-DNA. Furthermore, we find that A(T) shows favourable base-pairing properties with thymine and more surprisingly also with normal adenine. In conclusion, A(T) shows strong potential as a new fluorescent adenine analogue for monitoring changes within its microenvironment in DNA.