6522
J. Am. Chem. Soc. 1996, 118, 6522-6523
tion.7 Illustrative of this point, commercially available benzo-
triazole (4) has been shown to be transformed photochemically
at 77 K into the spectroscopically observable intermediate 6.8
This reaction is proposed to proceed from the lowest excited
singlet state of 4 (π,π*), leading initially to a detectable azoimine
5. 5 is stable only at low temperature and converts thermally
or photochemically to 6. Singlet 6 can react directly or undergo
intersystem crossing to the triplet which is capable of hydrogen
abstraction and thereby of serving as a potential agent for DNA
cleavage.
Triazole Photonucleases: A New Family of Light
Activatable DNA Cleaving Agents
Paul A. Wender,* Sofia M. Touami, Carole Alayrac, and
Ulrich C. Philipp
Department of Chemistry, Stanford UniVersity
Stanford, California 94305
ReceiVed February 28, 1996
Esperamicin, calicheamicin, dynemicin, neocarzinostatin, and
related DNA cleaving agents have attracted considerable interest
in recent years due in part to their highly potent antitumor
activity, novel mode of action, and potential service as reagents
in nucleic acid research.1,2 Common to all of these agents is
their ability to undergo inducible cycloaromatization to an aryl
or indenyl diradical which abstracts hydrogens from proximate
deoxyribosyl sites, leading to DNA scission.1-3 Efforts to
synthesize these natural products or superior analogs have
progressed impressively, resulting in a number of imaginative
strategies for the assembly of the enediyne precursors of the
DNA-damaging diradicals.4 In contrast, relatively little effort
has been directed at the investigation of simple aryl (mono)
radicals or related species as nucleic acid cleaving agents, even
though such intermediates are readily prepared and exhibit
similar reactivity to aryl diradicals,5 being implicated in the
mechanism of action of the above agents.6 Several years ago,
we started studies directed at the development of conceptually
new approaches to radical-based DNA cleaving agents and
describe below our initial investigation of a novel family of
activatable DNA cleaving agents represented by triazoles 1-3.
Agents 1-3, incorporating several structural and chromophore
variations of interest, were selected for cleavage studies. 1-(2-
Naphthoyl)benzotriazole (1) was formed quantitatively by
treatment of 4 with Et3N and 2-naphthoyl chloride. The
amidobenzotriazole 2 was obtained through a 1-(3-dimethyl-
aminopropyl)-3-ethylcarbodiimide-mediated coupling of ben-
zotriazole-5-carboxylic acid and aniline in the presence of
1-hydroxybenzotriazole in DMF (91%). Finally, naphthotriazole
3 was synthesized from 2,3-diaminonaphthalene by published
procedures.9
As a test of its competency as a radical generator, triazole 1
was photolyzed in ethanol at 300 and 350 nm. Products 7 and
8 were obtained, in accord with studies on benzotriazole itself,8
along with solvolysis products 9 and 10. When the photolysis
of 1 was carried out in CD3OD, deuterium incorporation (75%)
was observed. Photolysis of 3 produced 2-aminonaphthalene
(11, 80% isolated yield). Deuterium incorporation (>90%) was
observed when this reaction was carried out in THF-d8.
Photolysis of benzotriazole 2 in methanol or acetonitrile also
produced a photoextrusion product, 4-aminobenzanilide.
Our initial studies were guided by the mechanistic and
operational advantages offered by photoinducible radical forma-
(1) For recent reviews, see: Enediyne Antibiotics As Antitumor Agents;
Borders, D. B., Doyle, T. W., Eds.; Marcel-Dekker: New York, 1995.
Maier, M. E. Synlett 1995, 13-26. Nicolaou, K. C.; Dai, W. M. Angew.
Chem., Int. Ed. Engl. 1991, 30, 1387-1416. Tetrahedron Symposia-In-
Print Number 53; Doyle, T. W., Kadow, J. F., Eds.; Elsevier: Oxford, 1994;
Vol. 50, pp 1311-1538.
(2) For lead references on other nucleic acid cleaving agents, see: Singh,
U. S.; Scannell, R. T.; An, H.; Carter, B. J.; Hecht, S. M. J. Am. Chem.
Soc. 1995, 117, 12691-12699. Chen, C.-H.; Garin, M. B.; Sigman, D. S.
Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 4206-4210. Absalon, M. J.; Wu,
W.; Kozarich, J. W.; Stubbe, J. Biochemistry 1995, 34, 2076-2086. Dervan,
P. B. In Structure & Methods; Sarma, R. H., Sarma, M. H., Eds.; Adenine
Press: Schenectady, NY, 1990; Vol. 1, pp 37-50. Shields, T. P.; Barton,
J. K. Biochemistry 1995, 34, 15037-15048. Bernadou, J.; Meunier, B.
Angew. Chem., Int. Ed. Engl. 1995, 34, 746-769 and references cited
therein.
(3) (a) Bergman, R. G. Acc. Chem. Res. 1973, 6, 25-31. (b) Myers, A.
G. Tetrahedron Lett. 1987, 28, 4493-4496. Dedon, P. C.; Goldberg, I. H.
In Nucleic Acid Targeted Drug Design; Propst, C. L., Perun, T. J., Eds.;
Dekker: New York, 1992; pp 475-523.
(4) Significant contributions have been made by several groups, including
those of Bru¨ckner, Danishefsky, Doyle, Grierson, Hirama, Isobe, Kadow,
Kende, Krause, Krebs, Magnus, Maier, Myers, Nicolaou, Nuss, Saito,
Schreiber, Semmelhack, Suffert, Takahashi, and Terashima. For lead
references and examples, see: ref 1. Danishefsky, S. J.; Shair, M. D. J.
Org. Chem. 1996, 61,16-44. Myers, A. G.; Fraley, M. E.; Tom, N. J.;
Cohen, S. B.; Madar, D. J. Chem. Biol. 1995, 2, 33-43. Smith, A. L.;
Pitsinos, E. N.; Hwang, C.-K.; Mizuno, Y.; Saimoto, H.; Scarlato, G. R.;
Suzuki, T.; Nicolaou, K. C. J. Am. Chem. Soc. 1993, 115, 7612-7624.
Magnus, P. Tetrahedron 1994, 50, 1397-1418. Wood, J. L.; Porco, J. A.,
Jr.; Taunton, J.; Lee, A. Y.; Clardy, J.; Schreiber, S. L. J. Am. Chem. Soc.
1992, 114, 5898-5900. Wender, P. A.; Tebbe, M. J. Tetrahedron 1994,
50, 1419-1434.
The ability of these molecules to cleave DNA was determined
by their effectiveness in converting circular supercoiled DNA
(form I) to circular relaxed DNA (form II) and linear DNA (form
III). For this purpose, triazoles 1-3 (Figure 1) were irradiated
(6) Notable exceptions include studies on the use of trimethylene methane
diradicals from diazo extrusions and phenyl radicals from diazene and
diazonium ion decompositions: Bregant, T. M.; Groppe, J.; Little, R. D. J.
Am. Chem. Soc. 1994, 116, 3635-3636. Jebaratman, D. J.; Kugabalasooriar,
S.; Chen, H.; Arya, D. P. Tetrahedron Lett. 1995, 36, 3123-3126. Griffiths,
J.; Murphy, J. A. J. Chem. Soc., Chem. Commun. 1992, 24-26. See also:
Sullivan, R. W.; Coghlan, V. M.; Munk, S. A.; Reed, M. W.; Moore, H.
W. J. Org. Chem. 1994, 59, 2276-2278.
(7) Wender, P. A.; Beckham, S.; O’Leary, J. G. Synthesis 1994, 1278-
1282.
(8) For lead references, see: Shizuka, H.; Hiratsuka, H.; Jinguji, M.;
Hiraoka, H. J. Phys. Chem. 1987, 91, 1793-1797. Murai, H.; Torres, M.;
Strausz, O. P. J. Am. Chem. Soc. 1980, 102, 1421-1422. Claus, P.; Doppler,
T.; Gakis, N.; Georgarakis, M.; Giezendanner, H.; Gilgen, P.; Heimgartner,
H.; Jackson, B.; Ma¨rky, M.; Narasimhan, N. S.; Rosenkranz, H. J.; Wunderli,
A.; Hansen, H. J.; Schmid, H. Pure Appl. Chem. 1973, 33, 339-361.
Burgess, E. M.; Carithers, R.; McCullagh, L. J. Am. Chem. Soc. 1968, 90,
1923-1924. Boyer, H.; Selvarajan, R. J. Heterocycl. Chem. 1969, 6, 503-
506. Tsujimoto, K.; Ohashi, M.; Yonezawa, T. Bull. Chem. Soc. Jpn. 1972,
45, 515-519.
(5) Kryger, R. G.; Lorand, J. P.; Stevens, N. R.; Herron, N. R. J. Am
Chem. Soc. 1977, 99, 7589-7600. Scaiano, J. C.; Stewart, L. C. J. Am.
Chem. Soc. 1983, 105, 3609-3614. Bridger, R. T.; Russell, G. A. J. Am
Chem. Soc. 1963, 85, 3754-3766. Madhavan, V.; Schuler, R. H.; Fessenden,
R. W. J. Am. Chem. Soc. 1978, 100, 888-893.
(9) Hijazi, A.; Pfleiderer, W. Nucleotides Nucleosides 1986, 5, 243-
252.
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