Stannabenzene has not been isolated so far because of its high reactivity. In order to synthesize and isolate a stable stannabenzene, we have introduced two steric protection groups, the Tbt (2,4,6-tris[bis(trimethylsilyl)methyl]phenyl) or the Bbt (2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl) group on the tin atom and the t-butyl group on the 2-position, to the stannabenzene skeleton. Such a combination of steric protection groups was found to suppress the dimerization of stannabenzene to some extent, giving an equilibrated mixture of the corresponding stannabenzene and its dimer.

5-Bromouracil ((Br)U) was incorporated into three types of synthetic RNA and the products of the photoirradiated (Br)U-containing RNAs were investigated using HPLC and MS analysis. The photoirradiation of r(GCA(Br)UGC)(2) and r(CGAA(Br)UUGC)/r(GCAAUUCG) in A-form RNA produced the corresponding 2'-keto adenosine ((keto)A) product at the 5'-neighboring nucleotide, such as r(GC(keto)AUGC) and r(CGA(keto)AUUGC), respectively. The photoirradiation of r(CGCG(Br)UGCG)/r(C(m)GCAC(m)GCG) in Z-form RNA produced the 2'-keto guanosine ((keto)G) product r(CGC(keto)GUGCG), whereas almost no products were observed from the photoirradiation of r(CGCG(Br)UGCG)/r(C(m)GCAC(m)GCG) in A-form RNA. The present results indicate clearly that hydrogen (H) abstraction by the photochemically generated uracil-5-yl radical selectively occurs at the C2' position to provide a 2'-keto RNA product.

Charge transfer through DNA is of great interest because of the potential of DNA to be a building block for nanoelectronic sensors and devices. The photochemical reaction of 5-halouracil has been used for probing charge-transfer processes along DNA. We previously reported on unique charge transfer following photochemical reaction of 5-bromouracil within four-base π-stacks in Z-DNA. In this study, we incorporated a guanosine instead of a deoxyguanosine into Z-DNA, and found that electron transfer occurs in a different mechanism through four-base π-stacks.