COMMUNICATIONS
stabilities, the nucleobases close to the 3'-ends have to be
taken into account. Biological phenomena that concern the
accuracy of ribosomal translation should, particularly, be
newly analysed in terms of their codon context. In this sense,
we are extending the current studies towards a systematic
comparison of coded and recoded codon ± anticodon com-
plexes encountered during ribosomal tRNA slippage, in order
to reveal differences in the base-stacking patterns as a
[13] Effects of stabilization by tRNA-purine-37 are discussed, but have
only been quantified with respect to tRNA/tRNA-dimerizations so
far. See: C. Houssier, H. Grosjean, J. Biomol. Struct. Dyn. 1985, 3,
3
87 ± 408.
1
[
14] For the relevance of m G concerning frameshifting see: G. R. Björk,
EMBO J. 1999, 18, 1427 ± 1434.
[
15] a) J. Atkins, R. Gesteland in tRNA: Structure, Biosynthesis, and
Function (Eds.: D. Söll, U. RajBhandary), ASM Press, Washington
DC, 1995, pp. 471 ± 490; b) R. Gesteland, J. Atkins, Annu. Rev.
Biochem. 1996, 65, 741 ± 768; c) P. Farabaugh, Annu. Rev. Genet.
1996, 30, 507 ± 528.
[
15]
determinant for frameshift events.
Received: November 11, 1999 [Z14255]
[
1] a) B. Alberts, D. Bray, J. Lewis, M. Raff, K. Roberts, J. D. Watson,
Molecular Biology of the Cell, Garland, New York, 1995; b) C. M. T.
Spahn, K. H. Nierhaus, Biol. Chem. 1998, 379, 753 ± 772.
[
[
2] J. H. Cate, M. M. Yusupov, G. Z. Yusupova, T. N. Earnest, H. F.
Noller, Science 1999, 285, 2095 ± 2104.
3] a) G. M. Clore, A. M. Gronenborn, L. W. McLaughlin, J. Mol. Biol.
A Convenient and General Tin-Free Procedure
for Radical Conjugate Addition**
1
984, 174, 163 ± 173; b) G. M. Clore, A. M. Gronenborn, E. A. Piper,
L. W. McLaughlin, E. Graeser, J. H. van Boom, Biochem. J. 1985, 221,
37 ± 751; for codon ± anticodon interactions in general, see: c) S.
Cyril Ollivier and Philippe Renaud*
7
Yoshizawa, D. Fourmy, J. D. Puglisi, Science 1999, 285, 1722 ± 1725;
d) R. C. Morris, K. G. Brown, M. S. Elliott, J. Biomol. Struct. Dyn.
Radical reactions are becoming an extremely useful tool in
organic synthesis, particularly for the formation of carbon ±
carbon bonds in intra- and intermolecular processes.[ The
very rapid development of these reactions could be attributed
to the emergence of highly efficient ways to conduct them.
Among these methods, the tin hydride mediated addition of
radicals to activated alkenes has played a major role.[
However, the application of this reaction for the synthesis of
pharmaceuticals is severely limited by the toxicity of the tin
reagents and by the difficulty in removing traces of organotin
residues from the final products. Therefore, alternative ways
of running radical reactions are under intensive investiga-
1999, 16, 757 ± 774; e) V. I. Lim, G. V. Aglyamova, Biol. Chem. 1998,
379, 773 ± 781; f) D. Smith, M. Yarus, Proc. Natl. Acad. Sci. USA 1989,
86, 4397 ± 4401.
1]
[
4] W. Saenger, Principles of Nucleic Acid Structure, Springer, Berlin,
984, pp. 141 ± 149.
5] a) E. Westhof, P. Dumas, D. Moras, Acta Crystallogr. Sect. A 1988, 44,
12 ± 123; b) M. Sprinzl, C. Horn, M. Brown, A. Ioudovitch, S.
1
[
2]
1
Steinberg, Nucleic Acids Res. 1998, 26, 148 ± 153.
[
[
6] For examples of experimental references to interactions of this kind
see: a) D. Ayer, M. Yarus, Science 1986, 231, 393 ± 395; for theoretical
concepts such as ªThe Hypercycleº see also: b) M. Eigen, P. Schuster,
Naturwissenschaften 1978, 65, 341 ± 369.
1
7] For the natural occurrence and significance of m G see: a) G. R. Björk
in tRNA: Structure, Biosynthesis, and Function (Eds.: D. Söll, U.
RajBhandary), ASM Press, Washington DC, 1995, pp. 165 ± 205; b) S.
Yokoyama, S. Nishimura in tRNA: Structure, Biosynthesis, and
Function (Eds.: D. Söll, U. RajBhandary), ASM Press, Washington
[3]
tion. Recently, we have reported a modified version of the
[4]
Brown ± Negishi reaction where efficient hydroborations
with catecholborane and radical additions to enones and enals
were performed in a one-pot procedure (Scheme 1).[ This
oxygen-initiated reaction proved to be efficient with enones
and enals. However, other classical radical traps such as
unsaturated esters, amides, and sulfones failed to react.
Herein, we present an efficient procedure to run one-pot
hydroboration for radical addition to any kind of activated
alkenes. The reaction is based on the use of a Barton
5a]
1
DC, 1995, pp. 207 ± 223; for the preparation of m G building blocks for
automated solid-phase synthesis see: c) M. Sekine, T. Satoh, J. Org.
Chem. 1991, 56, 1224 ± 1227; d) P. F. Agris, A. Malkiewicz, A.
Kraszewski, K. Everett, B. Nawrot, E. Sochacka, J. Jankowska, R.
Guenther, Biochimie 1995, 77, 125 ± 134.
[
8] Linkers based on ethylene glycol, tri- and tetrakisethylene glycol
phosphate, and 1-hydroxy-propan-3-phosphate were optimized at
various length as loop replacements within the hairpin sequences
rUGGA-UUUU-UCCAG, rUCCAG-UUUU-UGGA, and rUGGA-
UUUU-GUCCA: W. Pils, R. Micura, unpublished results; see also:
a) S. Rumney, E. T. Kool, J. Am. Chem. Soc. 1995, 117, 5635 ± 5646;
b) F. Benseler, D.-j. Fu, J. Ludwig, L. W. McLaughlin, J. Am. Chem.
Soc. 1993, 115, 8483 ± 8484; c) A. C. Moses, A. Schepartz, J. Am.
Chem. Soc. 1997, 119, 11591 ± 11597; d) J. P. Bartley, T. Brown, A. N.
Lane, Biochemistry 1997, 36, 14502 ± 14511; e) M. Durant, K. Chevrie,
M. Chassignol, N. T. Thuong, J. C. Maurizot, Nucleic Acid. Res. 1990,
[6]
carbonate as radical chain transfer reagent (RCTR).
The failure of our modified version of the Brown ± Negishi
reaction with classical radical traps such as acrylate moieties
was interpreted as a consequence of an inefficient propaga-
tion step resulting from the reaction between the radical
adducts and B-alkylcatecholboranes. This inefficiency is
caused by the lower density of unpaired electrons at the
18, 6353 ± 6359; f) M. Y.-X. Ma, K. McCallum, S. C. Climie, R.
Kuperman, W. C. Lin, M. Sumner-Smith, R. W. Barnett, Nucleic
Acids Res. 1993, 21, 2585 ± 2589.
9] tRNA comprising m G (position 37) together with guanosine or 2'-
O-methylguanosine (position 34) is found in several organisms see:
ref. [5b].
Phe
1
[*] Prof. P. Renaud, C. Ollivier
Universit e de Fribourg
[
Institut de Chimie Organique
P e rolles, 1700 Fribourg (Switzerland)
Fax : ( 41)26-300-9739
[
[
10] R. Micura, Chem. Eur. J. 1999, 5, 2077 ± 2082.
11] a) L. Marky, K. Breslauer, Biopolymers 1987, 26, 1601 ± 1620; b) T.
Xia, D. H. Mathews, D. H. Turner in Comprehensive Natural Product
Chemistry, Vol. 8 (Eds.: D. Söll, S. Nishimura, P. Moore), Elsevier,
Oxford, UK, 1999, pp. 21 ± 47; c) M. Petersheim, D. H. Turner,
Biochemistry 1983, 22, 256 ± 263.
E-mail: philippe.renaud@unifr.ch
[**] Organoboranes in Radical Reactions. Part 4. This work was gener-
ously supported by the Fonds National Suisse de la Recherche
Scientifique. We thank Val e ry Weber for performing some preliminary
experiments. Parts 1 ± 3: see ref. [5].
[
12] P. Strazewski, Helv. Chem. Acta 1995, 78, 1112 ± 1143.
Angew. Chem. Int. Ed. 2000, 39, No. 5
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