Preparation of pyrenyl-modified nucleosides via Suzuki-Miyaura cross-coupling reactions

Article abstract of DOI:10.1055/s-2002-25349

The modified nucleosides 5-pyrenyl-2′-deoxyuridine (1) and 8-pyrenyl-2′-deoxyguanosine (2) were synthesized via palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of pyren-1-yl boronic acid (3) to either 5-iodo-2′-deoxyuridine (4), or 8-bromo-2′-deoxyguanosine (7), respectively. No protecting groups for the hydroxy and amino functions of the nucleoside are needed during the preparation. Both pyrene derivatives are suitable nucleoside models for the spectrosopic investigation of reductive electron transfer (in 1), or oxidative hole transfer (in 2).

Full text of DOI:10.1055/s-2002-25349

LETTER
687
Preparation of Pyrenyl-Modified Nucleosides via Suzuki–Miyaura
Cross-Coupling Reactions
P
N
reparationof
P
yr
i
e
nyl-M
c
odified
N
u
o
Technical University of Munich, Institute for Organic Chemistry and Biochemistry, Lichtenbergstr. 4, 85747 Garching, Germany
Fax +49(89)28913210; E-mail: wagenknecht@ch.tum.de
Received 29 January 2002
9
into the oligonucleotide. Despite the fact that spectro-
scopic measurements with this system have not been pub-
lished, the thymine-thymine dimer splitting was
Abstract: The modified nucleosides 5-pyrenyl-2 -deoxyuridine (1)
and 8-pyrenyl-2 -deoxyguanosine (2) were synthesized via palladi-
um-catalyzed Suzuki–Miyaura cross-coupling reactions of pyren-1-
yl boronic acid (3) to either 5-iodo-2 -deoxyuridine (4), or 8-bromo- interpreted as the chemical result of a reductive electron
-deoxyguanosine (7), respectively. No protecting groups for the transfer through the DNA base stack. This interpretation
2
hydroxy and amino functions of the nucleoside are needed during
the preparation. Both pyrene derivatives are suitable nucleoside
models for the spectrosopic investigation of reductive electron
transfer (in 1), or oxidative hole transfer (in 2).
is based mainly on the redox properties of the flavin inter-
calator in its reduced and deprotonated state and on the ab-
sence of a typical DNA base sequence dependence, which
should be observed in case of an oxidative hole hopping
Key words: charge transfer, nucleoside, cross-coupling, palladium,
pyrene
10
mechanism.
Until now suitable DNA assays for the time-resolved
spectroscopic investigation of reductive electron transfer
through DNA are elusive. Herein we want to present pre-
liminary results regarding the synthesis of 5-pyrenyl-2 -
deoxyuridine (1) and 8-pyrenyl-2 -deoxyguanosine (2) as
nucleoside model systems for the time-resolved spectro-
scopic investigation of the two different types of charge
transfer (electron transfer vs. hole transfer). In principle,
both compounds allow the later incorporation into DNA
duplexes via phosphoramidite chemistry. Pyrene deriva-
tives have been used previously as artificial DNA bases
by Kool et al. With respect to the relative redox proper-
ties we chose to attach a pyrenyl group (Py) to the nucle-
obases thymine (resp. uracil) and guanine (Figure 1). In
case of the uridine derivative 1, excitation of the pyrene
moiety leads to an intramolecular reductive electron trans-
Charge migration processes through DNA have been a
subject of an intense scientific debate over the last 10 to
1
–4
1
5 years. The motivation for this research is mainly fo-
cused on the biological consequences of these processes,
5
such as DNA damage, mutations, and cancer. Charge
transfer reactions through DNA have been initiated by
photoexcitation of suitable charge donors and have been
probed by various different methods, including fluores-
1
2
cence quenching, transient absorption spectroscopy,
11
3
electron spin resonance spectroscopy, and gel electro-
phoretic or HPLC analysis of lesions of the nucleic acids.4
It is important to emphasize that in most of these experi-
ments oxidative hole transfer processes have been ob-
served resulting in oxidative guanine damage at distant
0
fer yielding the corresponding uracil radical anion [E
sites on the nucleic acid. Spectroscopic efforts have fo-
+
12
0
–
13
cused on hole transport over short distances (10–20 Å)1,2
(Py /Py) = 1.28 V and E (dT/dT ) = –1.4 V]. In con-
trast, excitation of the pyrenyl group in the guanosine de-
rivative 2 results in formation of the guanine radical
while biochemical measurements have explored oxidative
guanine damage at more distant sites (30–200 Å).6
0
cation as the product of an oxidative hole transfer [E (Py/
On the other hand, reductive electron transfer through
DNA duplexes is currently used extensively in DNA chip
technology and DNA nanotechnology without under-
standing the mechanism of this type of charge migration.7
Only a few publications deal with a reductive electron
transfer through DNA. In the past, Barton et al. investigat-
ed charge transfer reactions using intercalated and co-
valently tethered metal complexes as charge donors and
acceptors which can be interpreted in parts as electron
–
12
0
+
14
Py ] = –2.1 V and E (dG /dG) = 1.3 V. Both charge
transfer assignments are proven by ps transient absorp-
15
tion experiments using 5-(1-pyrenoyl)-2 -deoxyuridin
and using benzo{a}pyrenyl-2 -deoxygu-anosine conju-
16
gates.
Only for the preparation of nucleoside 1 exists a published
procedure by Netzel et al.11 using a palladium-catalyzed
Stille-type cross coupling of 1-pyrenyl-(tributyl)-stan-
nane with a fully protected 5-iodo-2 -deoxyuridine deriv-
ative. According to the authors, a glove box is needed
during this procedure in order to ensure that moisture and
air are excluded from the preparation. Our new approach
to synthesize the pyrene-modified nucleosides 1 and 2
was to apply the palladium-catalyzed Suzuki–Miyaura-
type cross coupling of pyren-1-yl boronic acid (3) to the
halogenated nucleosides. In general, Suzuki–Miyaura-
8
transfer reactions. More recently, Carell et al. described
the repair of thymine-thymine dimers through DNA-me-
diated electron transfer from a distant flavine derivative as
an artificial base which was synthetically incorporated
Synlett 2002, No. 5, 03 05 2002. Article Identifier:
1
©
437-2096,E;2002,0,05,0687,0691,ftx,en;G02302ST.pdf.
Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214

6
88
N. Amann, H.-A. Wagenknecht
LETTER
According to this new synthetic strategy, the nucleoside 1
was prepared via the cross coupling of pyren-1-yl boronic
acid (3) to 5-iodo-2 -deoxyuridine (4) using Pd(PPh ) as
3
4
the catalyst and THF/MeOH/H O = 2:1:2 as the solvent
2
(
Scheme 1). The starting material 4 is commercially avail-
able. The two hydroxy groups of the 2 -deoxyribose moi-
ety of 4 were not protected. A strong base (NaOH) was
required in order to get the desired sterically hindered
coupling product 1 in sufficient yield (70%). The pyren-1-
yl boronic acid (3) was synthesized according to a combi-
nation of different literature procedures by lithiation of 1-
bromopyrene (5) at 0 °C and treatment with trimethyl
borate at –78 °C and subsequent acidic workup at room
18
temperature. Interestingly, when the lithiation of 1-bro-
mopyrene (5) was performed at –78 °C, a rather low yield
of the desired boronic acid 3 (40%) was obtained whereas
the lithiation of 5 at 0 °C results in an increased yield of 3
(
73%). We also prepared 3 ,5 -di-O-acetyl-2 -deoxy-5-
19
iodo-uridine (6) and used it for the palladium-catalyzed
cross coupling with the boronic acid 3 in dry THF and
Figure 1 Pyrene-modified nucleosides 1 and 2. Excitation of the
pyrene moiety at = 340 nm results in either reductive electron trans-
fer (ET) yielding the uracil radical anion (in 1) or oxidative hole trans-
fer (HT) yielding the guanine radical cation (in 2).
Et N as the base. The overall yield of 1 after deprotection
3
of the intermediate acetylated pyrene-modified uridine
using NaOMe/MeOH was slightly lower than the direct
cross coupling of the unprotected starting material 4 with
the boronic acid 3 (55%). The structure of the nucleoside
1
was confirmed by different spectroscopic measure-
type couplings are easier to handle because they work in
moist or even aqueous solutions and under air, too. Many
boronic acids are commercially available and inexpen-
ments, including ESI mass spectrometry and 2D-NMR
experiments, such as DQF-COSY and HMQC.20
sive, they are non-toxic and they tolerate the presence of The second modified nucleoside, 8-pyrenyl-2 -deoxy-
some unprotected functional groups. Suzuki–Miyaura- guanosine (2) was prepared in a similar fashion
type couplings have been performed for the preparation of (Scheme 2). The starting material 8-bromo-2 -deoxy-
1
7
arylated and alkenylated purines but have not yet been guanosine (7) was obtained in good yield (85%) via bro-
used for the direct synthesis of aryl-modified nucleosides. mination of 2 -deoxyguanosine (8) using N-bromo-
Scheme 1 Synthesis of 5-Pyrenyl-2 -deoxyuridin (1): (a) 1. n-BuLi (1.1 equiv), Et O, 0 °C, 30 min; 2. B(OCH ) (5.0 equiv), –78 °C, 6 h,
2
3 3
+
then r.t., 20 h. 3. H O , r.t., 3 h; 73%, (b) 3 (1.0 equiv), Pd(PPh ) (0.1 equiv), NaOH (20 equiv), THF/MeOH/H O = 2:1:2, reflux, 20 h; 70%;
3
3 4
2
(
c) Ac O (2.5 equiv), pyridine, r.t., 20 h; (d) 3 (1.0 equiv), Pd(PPh ) (0.1 equiv), Et N (4.2 equiv), THF, reflux, 20 h; (e) NaOMe (1.0 equiv),
2
3
4
3
MeOH, r.t., 18 h; 55% (d + e).
Synlett 2002, No. 5, 687–691 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Preparation of Pyrenyl-Modified Nucleosides
689
Scheme 2 Synthesis of 8-Pyrenyl-2 -desoxyguanosin (2): (a) N-bromosuccinimide (1.1 equiv), H O, r.t., 2 h; 85%; (b) 3 (1.0 equiv),
2
Pd(PPh ) (0.1 equiv), NaOH (20 equiv), THF/MeOH/H O = 2:1:2, reflux, 20 h; 65%.
3
4
2
2
1
succinimide in H O. The subsequent coupling of 7 to citation wavelength for both nucleosides was chosen to be
2
pyren-1-yl boronic acid (3) was performed in THF/
= 340 nm. In the steady-state fluorescence spectra, both
MeOH/H O = 2:1:2 and using Pd(PPh ) as the catalyst. compounds display an emission profile, which is different
2
3 4
Both, the hydroxy groups of the 2 -deoxyribose part of 7, from pure pyrene indicating a strong electronic interaction
and the exocyclic amino function in position 2 of the gua- between the nucleoside moiety and the covalently at-
nine moiety of 7 were not protected during the coup- tached pyrene. In fact, preliminary femtosecond-resolved
ling. After purification (65% yield), the pyrene-modified transient absorption data indicates charge transfer pro-
24
nucleoside 2 has been characterized by different spectro- cesses in both pyrene-modified nucleosides. Interesting-
scopic measurements, including ESI mass spetrometry ly, when excited at = 340 nm, the uridine derivative 1
2
2
and 2D-NMR experiments.
shows a remarkable bathochromic shift of the emission
wavelength in comparison between MeCN ( em = 422
nm) and MeOH ( em = 482 nm) as a solvent, which has
also been observed previously. This observation was in-
terpreted by protonation of the uracil radical anion. But,
according to Steenken et al., protonation of the uracil rad-
The pyrene-modified nucleosides 1 and 2 were character-
ized by UV/VIS absorbance and steady-state fluorescence
spectroscopy. The measurements were performed in
MeCN and MeOH as typical examples of organic solvents
without (MeCN) or with hydrogen bonding capabilities
15
2
3
ical anion by MeOH is rather unlikely since the pK value
a
(
MeOH). In case of the uridine derivative 1, the previous-
24
1
5
of the protonated uracil radical is 6.9. Another explana-
tion could be the solvation of the charge-separated species
ly published absorbance and emission spectra could be
reproduced. As expected, the UV/Vis spectrum of both
compounds, 1 and 2, exhibit a similar shape of absorbance
in both solvents. Based on this absorbance spectra, the ex-
25
of 1 in MeOH via hydrogen bonding. Interestingly, the
guanosine derivative fluorescence does not display this
Figure 2 UV/Vis absorbance spectra (left) and steady-state fluorescence spectra (right) of the pyrene-modified nucleoside 2 ( A = 0.2 at
1
5
=
340 nm). The corresponding absorption and emission spectra of 1 have been published previously by Netzel et al.
exc
Synlett 2002, No. 5, 687–691 ISSN 0936-5214 © Thieme Stuttgart · New York

6
90
N. Amann, H.-A. Wagenknecht
LETTER
difference between MeCN ( em = 477 nm) and MeOH
( em = 485; Figure 2). Currently, time-resolved spectro-
scopic measurements on the femtosecond time scale are
conducted in order to detect the intermediates by transient
absorption, to characterize the nature of the charge-sepa-
rated species, and, finally, to explore the detailed mech-
anisms of the charge transfer processes observed in the
(7) (a) Boon, E. M.; Ceres, D.; Drummond, T. G.; Hill, M. G.;
Barton, J. K. Nat. Biotechnol. 2000, 18, 1096. (b) Jackson,
N. M.; Hill, M. G. Curr. Opin. Chem. Biol. 2001, 5, 209.
(c) Fink, H.-W.; Schönenberger, C. Nature (London) 1999,
398, 407. (d) Porath, D.; Bezryadin, A.; de Vries, S.;
Dekker, C. Nature (London) 2000, 403, 635.
8) Murphy, C. J.; Arkin, M. R.; Jenkins, Y.; Ghatlia, N. D.;
Bossmann, S. H.; Turro, N. J.; Barton, J. K. Science
(Washington, D.C.) 1993, 262, 1025.
9) Schwögler, A.; Burgdorf, L. T.; Carell, T. Angew. Chem. Int.
Ed. 2000, 39, 3918.
(
(
2
6
pyrene-modified nucleosides 1 and 2.
In this communication, we present a new approach for the
synthesis of pyrene-modified nucleosides via palladium-
catalyzed Suzuki–Miyaura-type cross couplings. This
protocol is very versatile and can be extended to other nu-
cleosides as well as to other aryl boronic acids. The two
synthesized pyrene-modified nucleosides 1 and 2 are suit-
able as nucleoside models for electron vs. hole transfer.
(
10) (a) Giese, B.; Spichty, M. Chem. Phys. Chem 2000, 1, 195.
(b) Giese, B.; Amaudrut, J.; Köhler, A.-K.; Spormann, M.;
Wessely, S. Nature (London) 2001, 412, 318.
11) Kool, E. T.; Morales, J. C.; Guckian, K. M. Angew. Chem.
Int. Ed. 2000, 39, 990.
(
(
12) Kubota, T.; Kano, J.; Uno, B.; Konse, T. Bull. Chem. Soc.
Jpn. 1987, 60, 3865.
(
(
13) Hissung, A.; Sonntag, C. Int. J. Radiat. Biol. 1979, 35, 449.
14) Steenken, S.; Jovanovic, S. V. J. Am. Chem. Soc. 1997, 119,
Acknowledgement
617.
We are grateful to Prof. Horst Kessler, Technical University of Mu-
nich, for his generous support.
(15) Netzel, T. L.; Zhao, M.; Nafisi, K.; Headrick, J.; Sigman, M.
S.; Eaton, B. E. J. Am. Chem. Soc. 1995, 117, 9119.
(
16) (a) O’Connor, D.; Shafirovich, V. Y.; Geacintov, N. E. J.
Phys. Chem. 1994, 98, 9831. (b) Shafirovich, V. Y.;
References
Courtney, S. H.; Ya, N.; Geacintov, N. E. J. Am. Chem. Soc.
1
995, 117, 4920.
17) Havelková, M.; Dvorák, D.; Hocek, M. Synthesis 2001,
704.
(
1) (a) Arkin, M. R.; Stemp, E. D. A.; Holmlin, R. E.; Barton, J.
(
(
K.; Hörmann, A.; Olson, E. J. C.; Barbara, P. F. Science
1
1
996, 273, 475. (b) Fukui, K.; Tanaka, K. Angew. Chem. Int.
Ed. 1998, 37, 158. (c) Kelley, S. O.; Barton, J. K. Science
999, 283, 375. (d) Jean, J. M.; Hall, K. B. Proc. Natl. Acad.
18) The crude product was purified by column chromatography
on silica gel (hexane:EtOAc = 20:1, then EtOH) yielding a
1
pale yellow solid. R = 0.42 (hexane:EtOAc = 3:1). All
f
Sci. U.S.A. 2001, 98, 37. (e) Kawai, M.; Lee, M. J.; Evans,
K. O.; Nordlund, T. M. J. Fluoresc. 2001, 11, 23.
spectroscopic data of 3 were in agreement with the published
data in: (a) Suenaga, H.; Nakashima, K.; Mizuno, T.;
Takeuchi, M.; Hamachi, I.; Shinkai, S. J. Chem. Soc., Perkin
Trans. 1 1998, 1263. (b) Beinhoff, M.; Weigel, W.; Jurczok,
M.; Rettig, W.; Modrakowski, C.; Brüdgam, I.; Hartl, H.;
Schlüter, A. D. Eur. J. Org. Chem. 2001, 3819.
(
f) Larsen, O. F. A.; van Stokkum, I. H. M.; Gobets, B.; van
Grondelle, R.; van Amerongen, H. Biophys. J. 2001, 81,
115.
2) (a) Stemp, E. D. A. J. Am. Chem. Soc. 1997, 119, 2921.
b) Lewis, F. D.; Liu, X.; Liu, J.; Miller, S. E.; Hayes, R. T.;
Wasielewski, M. R. Nature (London) 2000, 406, 51.
c) Wan, C.; Fiebig, T.; Schiemann, O.; Barton, J. K.;
Zewail, A. H. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 14052.
d) Shafirovich, V.; Dourandin, A.; Huang, W.; Luneva, N.
P.; Geacintov, N. E. J. Phys. Chem. B 1999, 103, 10924.
e) Wagenknecht, H.-A.; Rajski, S. R.; Pascaly, M.; Stemp,
E. D. A.; Barton, J. K. J. Am. Chem. Soc. 2001, 123, 4400.
f) Hess, S.; Götz, M.; Davis, W. B.; Michel-Beyerle, M.-E.
1
(
(
(
19) The crude product was purified by column chromatography
on silica gel (CH Cl /acetone = 4:1) yielding a white solid.
2
2
(
R = 0.74 (CH Cl /acetone = 4:1). All spectroscopic data of
f
2
2
6
were in agreement with the published data in: Robins, M.
(
J.; Barr, P. J. J. Org. Chem. 1983, 48, 1854.
(
20) The crude product was purified by column chromatography
on silica gel (CH Cl /acetone = 4:1 then EtOAc/
(
2
2
MeOH = 10:1) yielding a pale yellow solid (70%).
Analytical HPLC (RP-18 column, gradient A/B = 10:90 to
(
J. Am. Chem. Soc. 2001, 123, 10046. (g) Lewis, F. D.; Wu,
Y. J. Photochem. Photobiol., C 2001, 2, 1.
9
0
9
0:10 over 45 min, A = MeCN + 0.1% TFA, B = H O +
.1% TFA) was performed to ensure the purity of 1 of >
2
(
(
3) Schiemann, O.; Turro, N. J.; Barton, J. K. J. Phys. Chem. B
9.5%. Spectroscopical Data of 1: R = 0.65 (EtOAc/MeOH/
f
2000, 104, 7214.
H O = 10:1:0.5). NMR signals were assigned based on 2D
2
4) (a) Arkin, M. R.; Stemp, E. D. A.; Coates Pulver, S.; Barton,
J. K. Chem. Biol. 1997, 4, 389. (b) Nakatani, K.; Dohno, C.;
Saito, I. J. Am. Chem. Soc. 1999, 121, 10854. (c) Williams,
T. T.; Odom, D. T.; Barton, J. K. J. Am. Chem. Soc. 2000,
1
NMR measurements (DQF-COSY, HMQC). H NMR (500
MHz, CD OD): = 2.29 (m, J = 6.4 Hz, 2 H, 2 -H), 3.50–
3
3.60 (ddd, J = 12.0 Hz, 3.3 Hz, 2 H, 5 -H), 3.84 (m, J = 3.2
Hz, 1 H, 3 -H), 4.31 (m, J = 4.3 Hz, 1 H, 4 -H), 6.35 (t,
122, 9048. (d) Schuster, G. B. Acc. Chem. Res. 2000, 33,
J = 6.6 Hz, 1 H, 1 -H), 7.84–8.14 (m, 9 H, Pyren-H), 8.21 (s,
253. (e) Giese, B. Acc. Chem. Res. 2000, 33, 613.
1
1
H, H-6) ppm; additional signals in H NMR (250 MHz, d -
6
(
5) (a) O’Neill, P.; Fielden, M. Adv. Radiat. Biol. 1993, 17, 53.
b) Wang, D.; Kreutzer, D. A.; Essigmann, J. M. Mutat. Res.
998, 400, 99.
6) (a) Núñez, M. E.; Hall, D. B.; Barton, J. K. Chem. Biol. 1999,
, 85. (b) Henderson, P. T.; Jones, D.; Hampikian, G.;
Schuster, G. B. Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 8353.
DMSO): = 4.79 (t, 1 H, 5 -OH), 5.24 (d, 1 H, 3 -OH), 11.64
(
1
1
3
1
(
s, br, 1 H, NH) ppm. C{ H} NMR (75 MHz, CD OD):
3
=
174.87, 174.13, 167.41, 163.91, 153.37, 153.15, 144.63,
(
1
1
44.07, 134.89, 134.29, 134.13, 133.93, 131.21, 131.01,
30.45, 129.49, 127.94, 126.83, 103.76, 104.41, 90.16 (4 -
6
C), 87.76 (1 -C), 73.42 (3 -C), 62.67 (5 -H), 42.52 (2 -C)
+
+
ppm. ESI-MS: m/z = 429 [M + H] , 451 [M + Na] , 857 [2
M + H] , 879 [2 M + Na] .
+
+
Synlett 2002, No. 5, 687–691 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Preparation of Pyrenyl-Modified Nucleosides
691
(
21) All spectroscopic data of 7 were in agreement with the
published data: Gannett, P.; Sura, T. P. Synth. Commun.
solubility of 2 in suitable NMR solvents. ESI-MS: m/z = 468
+
+
+
+
[M + H] , 490 [M + Na] , 936 [2 M + H] , 959 [2 M + Na] .
(23) Steady-state fluorescence spectroscopy was performed at r.t.
on a Spex Fluoromax II spectrometer. The emission spectra
are corrected according to detection system variation with
wavelength. UV/Vis absorbance spectroscopy was
performed at r.t. on a Varian Cary 50 photometer. Dry
solvents (Fluka puriss. over molecular sieve, water < 0.01%)
were used for the measurements. The septum-closed
cuvettes were filled under argon.
1993, 23, 1611.
(22) The crude product was purified by column chromatography
on silica gel (CH Cl /acetone = 4:1 then EtOAc/
2
2
MeOH = 10:1 then EtOAc/MeOH/H O = 10:1:0.5) yielding
2
a yellow solid (65%). Analytical HPLC (RP-18 column,
gradient A/B = 10:90 to 90:10 over 45 min, A = MeCN +
0
.1% TFA, B = H O + 0.1% TFA) was performed to ensure
2
the purity of 2 of > 99.5%. R = 0.73 (EtOAc/MeOH/
f
H O = 6:2:1). NMR signals were assigned based on 2D-
NMR measurements (DQF-COSY, HMQC). H NMR (500
(24) Amann, N.; Pandurski, E.; Wagenknecht, H.-A.; Fiebig, T.
in preparation.
2
1
MHz, CD OD): = 1.98 (m, J = 13.4 Hz, 5.8 Hz, 1 H, 2 -H),
(25) Steenken, S. Free Rad. Res. Commun. 1992, 16, 349.
(26) Currently, time-resolved spectroscopic measurements on the
femtosecond time scale are performed in order to detect and
characterize the short-lived intermediates by their transient
absorption: Amann, N.; Pandurski, E.; Wagenknecht, H.-A.;
Fiebig, T. in preparation.
3
3
.05 (m, 1 H, 2 -H), 3.58–3.72 (m, J = 9.9 Hz, 8.9 Hz, 4.2
Hz, 3 H, 5 -H, 4 -H), 4.32 (m, 1 H, 3 -H), 5.75 (t, J = 7.5 Hz,
H, 1 -H), 7.99–8.27 (m, 9 H, Pyren-H) ppm; additional
1
1
signals in H NMR (250 MHz, D -DMSO): = 4.93 (m, 2 H,
6
5
-OH, 3 -OH), 6.47 (s br, 2 H, NH ), 10.87 (s br, 1 H, NH)
2
13
ppm; no C NMR data could be obtained due to the low
Synlett 2002, No. 5, 687–691 ISSN 0936-5214 © Thieme Stuttgart · New York