A two-phase bromination process using tetraalkylammonium hydroxide for the practical synthesis of α-bromolactones from lactones.

A simple and efficient method for α-brominating lactones that affords α-bromolactones under mild conditions using tetraalkylammonium hydroxide (R4N+OH-) as a base was developed. Lactones are ring-opened with Br2 and a substoichiometric amount of PBr3, leading to good yields of the corresponding α-bromocarboxylic acids. Subsequent intramolecular cyclization over 1 h using a two-phase system (H2O/CHCl3) containing R4N+OH- afforded α-bromo lactones in good yields. This method can be applied at the 10 mmol scale using simple operations. α-Bromo-δ-valerolactone, which is extremely reactive and difficult to isolate, could be isolated and stored in a freezer for about one week using the developed method. Optimizing the solvent for environmentally friendly large-scale syntheses revealed that methyl ethyl ketone (MEK) was as effective. In addition, in situ-generated α-bromo-δ-valerolactone was directly converted into a sulfur-substituted functional lactone without difficulty by reacting it with a sulfur nucleophile in one pot without isolation. This new bromination system is expected to facilitate the industrial use of α-bromolactones as important intermediates.

Recognition of a bulged RNA by peptides derived from the influenza NS1 protein.

A competition assay for RNA binding by the influenza virus NS1 protein using model RNAs, U6-45, corresponding to U6 snRNA revealed that deletion of each of the three bulged-out parts reduced the NS1 protein binding and, in contrast, by deleting all three of the bulged-out parts, simultaneously, and thus producing a double-stranded RNA, the binding was recovered. A common feature of target RNAs of the NS1 protein, U6 snRNA, poly(A) and viral RNA, is the stretch of 'bulged-out' A residues. Thus, the NS1 protein was found to recognize either the stretch of 'bulged-out' A residues or dsRNA which is also a target of the NS1 protein. Furthermore, a basic peptide, NS1-2, derived from the helix-2 of the RNA binding site of NS1 protein was designed and its binding to the U6 snRNA was analysed by using a model RNA for U6 snRNA, U6-34. The NMR signals due to H8/H6 and H1' of U6-34 were assigned and their changes upon binding of NS1-2 were analysed. It was indicated that NS1-2 interacts with the residues in the bulge-out region of U6-34. These results suggest that NS1-2 recognizes the U6 snRNA in a similar manner to NS1 protein.

Solution structure of an RNA fragment with the P7/P9.0 region and the 3'-terminal guanosine of the tetrahymena group I intron.

In the second step of the two consecutive transesterifications of the self-splicing reaction of the group I intron, the conserved guanosine at the 3' terminus of the intron (omegaG) binds to the guanosine-binding site (GBS) in the intron. In the present study, we designed a 22-nt model RNA (GBS/omegaG) including the GBS and omegaG from the Tetrahymena group I intron, and determined the solution structure by NMR methods. In this structure, omegaG is recognized by the formation of a base triple with the G264 x C311 base pair, and this recognition is stabilized by the stacking interaction between omegaG and C262. The bulged structure at A263 causes a large helical twist angle (40 +/- 80) between the G264 x C311 and C262 x G312 base pairs. We named this type of binding pocket with a bulge and a large twist, formed on the major groove, a "Bulge-and-Twist" (BT) pocket. With another twist angle between the C262 x G312 and G413 x C313 base pairs (45 +/- 100), the axis of GBS/omegaG is kinked at the GBS region. This kinked axis superimposes well on that of the corresponding region in the structure model built on a 5.0 A resolution electron density map (Golden et al., Science, 1998, 282:345-358). This compact structure of the GBS is also consistent with previous biochemical studies on group I introns. The BT pockets are also found in the arginine-binding site of the HIV-TAR RNA, and within the 16S rRNA and the 23S rRNA.