Ogasawara and co-workers have reported the use of 8-substituted dG derivatives that provide reversible duplex regulation via a light induced trans-cis isomerization.⁽¹⁾ The trans isomer of 8-styryl-2'-deoxyguanosine (8STG) is one such photochromic nucleoside (PCN). When a 12-bp duplex containing 8STG is irradiated for 5 minutes at 370 nm, the double bond isomerizes to the cis geometry with 86% conversion. Subsequent irradiation for 2 minutes at 254 nm returns the double bond to the trans geometry with 94% conversion. Both trans and cis isomers are thermally stable but readily interconvert at room temperature upon irradiation with light of the appropriate wavelength. The Tm value of the duplex containing a trans-PCN is 7.9 degC higher than the Tm value of the same duplex containing a cis-PCN. When three 8STG insertions are inserted into a 20-bp duplex, the trans-PCNs permit duplex formation whereas the cis-PCNs cause denaturation of the duplex. This phenomenon is evidenced by changes in the circular dichroism spectra before and after irradiation of the duplex containing trans-PCNs at 370 nm. Conversely, when the single strands containg cis-PCNs are irradiated at 254 nm hybridization occurs as the trans isomer is formed.
Substitution of other aromatic moieties for the phenyl ring provides PCNs that operate at different wavelengths. For example with 8-(2-napthalen-2-yl)vinly-2'-deoxyguanosine (8NVG) the trans to cis conversion occurs with 410 nm irradiation and reverts at 290 nm and with 8-(2-fluoren-2-yl)vinyl-2'-deoxyguanosine (8FVG)) the trans to cis conversion occurs with 420 nm irradiation and reverts at 310 nm. 8STG, 8NVG, and 8FVG all have the common synthetic precursor 8-vinyl-dG. Thus we also offer PR3335 as a versatile synthetic intermediate for the preparation of these and other PCNs.

Ref:

1. (a) Ogasawara, S.; Saito, I.; Maeda, M. Tetr. Lett., 2008, 49, 2479-82. (b) Ogasawara, S.; Maeda, M. Angew. Chem. Int. Ed., 2008, 47, 8839-42.