Scheme 3 Reagents and conditions: (a) TFA, rt, 92%; (b) 1a, DCC, HOBt, i-Pr2NEt, NMP, rt; (c) 1% TFA–CH2Cl2, rt (77%, 2 steps).
2.99–2.97 (m, 2H), 2.94 (br s, 2H), 2.80 (dd, 1H, J = 12.6, 12.2 Hz), 2.57
tion of the (+)-biotin pentafluorophenyl ester (Bio-OPfp) and
deprotection of the Ns group gave the secondary amines 10a,b.
(d, 1H, J = 12.2 Hz), 2.01 (t, 2H, J = 7.3 Hz), 1.62–1.24 (m, 18H); 13C
NMR (DMSO-d6, 100 MHz): d 194.9, 171.9, 162.8, 138.9, 137.2, 136.8,
Attachment of 10a,b to the resin 2 was induced by i-Pr2NEt, and
136.8, 130.0, 129.8, 128.9, 128.9, 61.1, 59.3, 55.5, 49.6, 48.6, 46.8, 41.9,
subsequent reduction of the azide group with SnCl2, PhSH and
39.9, 39.9, 38.3, 35.2, 29.2, 28.5, 28.2, 28.1, 26.3, 25.9, 25.4; HRMS (FAB):
Et3N afforded the amines 1a,b. Confirmation of the structures
of 1a,b was determined by examination of 11a,b† after
cleavage from the resin. As shown in Scheme 2, the alcohol type
probe precursor 1c was synthesized by a similar procedure with
1a,b. Condensation of the alcohol 4 and the sulfonamide 12.5c
under Mitsunobu conditions and switching from the THP group
to TBS group afforded 15. After removal of the Alloc-group,
installation of the biotin unit and removal of the Ns-group gave
the secondary amine 16. Loading 16 onto the resin 2 and
deprotecting the TBS group provided 1c, the structure of which
was also confirmed by conversion to 17.†
calcd for C33H48N5O3S (M + H)+: 594.3477, found: 594.3470. 11b: 1H
NMR (DMSO-d6, 400 MHz): d 8.87 (br s, 1H), 8.30 (br s, 1H), 7.77 (d, 4H,
J = 8.3 Hz), 7.68–7.63 (m, 4H), 6.39 (br s, 1H), 4.30–4.25 (m, 3H),
4.17–4.10 (m, 3H), 3.12–3.93 (m, 3H), 2.93 (br s, 2H), 2.80 (dd, 1H, J =
12.2, 5.1 Hz), 2.56 (d, 1H, J = 12.2 Hz), 2.07 (t, 2H, J = 7.8 Hz), 1.76–1.74
(m, 2H), 1.51–1.08 (m, 8H); 13C NMR (DMSO-d6, 100 MHz): d 195.1,
173.0, 163.1, 140.9, 137.6, 136.7, 136.5, 130.2, 130.0, 129.1, 128.5, 61.4,
59.5, 55.6, 55.1, 53.3, 49.8, 48.7, 35.7, 35.3, 28.4, 28.2, 26.2, 25.4; HRMS
(FAB): calcd for C28H38N5O3S (M + H)+: 524.2695, found: 524.2708. 17:
1H NMR (DMSO-d6, 400 MHz): d 8.85 (br s, 1H), 7.95 (br s, 1H), 7.75 (d,
2H, J = 8.1 Hz), 7.68 (d, 2H, J = 8.3 Hz), 7.61 (d, 2H, J = 8.3 Hz), 7.50
(d, 2H, J = 8.1 Hz), 6.36 (br s, 1H), 5.14 (s, 2H), 4.26–4.19 (m, 3H),
4.08–4.05 (m, 1H), 3.09–3.04 (m, 3H), 2.88 (br s, 2H), 2.75 (dd, 1H, J =
12.4, 5.1 Hz), 2.51 (d, 1H, J = 12.4 Hz), 2.05 (s, 3H), 2.02 (t, 2H, J = 7.4
Hz), 1.71 (t, 2H, J = 7.1 Hz), 1.52–1.22 (m, 8H); 13C NMR (DMSO-d6, 100
MHz): d 195.0, 172.7, 170.4, 162.7, 145.4, 141.3, 136.5, 136.2, 130.3,
129.9, 129.8, 127.7, 64.8, 61.0, 59.2, 55.4, 49.7, 48.5, 44.8, 39.8, 35.5, 35.1,
28.3, 28.0, 26.1, 25.2, 20.7; HRMS (FAB): calcd for C30H39N4O5S (M +
H)+: 567.2641, found: 567.2655.
As shown in Scheme 3, the utility of the probe precursor 1a
was demonstrated by synthesis of the photoaffinity probe 20 for
investigation of the g-secretase. The g-secretase may be
involved in the generation of an amyloid b-peptide (Ab), which
is implicated in Alzheimers’ disease (AD).8 Since the g-
secretase inhibitor may be important as a therapeutic agent for
AD, numerous inhibitors have been investigated. Recently,
researchers at Elan reported that N-[N-3,5-difluorophenylace-
tyl- -alanyl-]-S-phenylglycine-tert-butyl ester (DAPT 18) ex-
L
hibited excellent inhibitory activity toward g-secretase.9 Our
preliminary investigation of the structure–activity relationship
of DAPT proved that modification of the C-terminal of DAPT
18 to a benzyl amide maintained its activity.10 Thus, incorpora-
tion of the labelling moiety into the C-terminal of 18 seemed
appropriate. Attachment of the carboxylic acid 19 readily
derived from 18 with the resin 1a was performed in the presence
of DCC and HOBt. Cleavage from the resin under acidic
conditions (1% TFA–CH2Cl2) afforded 20 in high purity
without any purification. The cross-linking experiment of the
probe 20 with g-secretase was carried out in our laboratories, the
results of which will be reported elsewhere.
1 For a review of photo-affinity labelling, see:(a) F. Kotozyba-Hilbert, I.
Kapfer and M. Goeldner, Angew. Chem., Int. Ed. Engl., 1995, 34, 1296;
(b) G. Dorman and G. D. Prestwich, Biochemistry, 1994, 33, 5661.
2 A. Singh, E. R. Thorton and F. H. Westheimer, J. Biol. Chem., 1962,
237, 3006.
3 (a) Y. Hatanaka, U. Kempin and P. Jong-Jip, J. Org. Chem., 2000, 65,
5639; (b) Y. Hatanaka, H. Hashimoto and Y. Kanaoka, J. Am. Chem.
Soc., 1998, 120, 453.
4 B. A. Gilbert and R. R. Rando, J. Am. Chem. Soc., 1995, 117, 8061.
5 (a) T. Kan, H. Kobayashi and T. Fukuyama, Synlett, 2002, 1338; (b) Y.
Hidai, T. Kan and T. Fukuyama, Tetrahedron Lett., 1999, 40, 4711; (c)
Y. Hidai, T. Kan and T. Fukuyama, Chem. Pharm. Bull., 2000, 48,
1570.
6 B. D. Douty, J. M. Salvino, P. R. Seoane and R. E. Dolle, Bioorg. Med.
Chem. Lett., 1995, 5, 363.
In conclusion, the polymer-supported probe precursors 1a–c
may be powerful tools for the preparation of photoaffinity
probes. It should be noted that the hydroxyl group of 1c was
readily converted to the corresponding halide, which could be
reacted with several nucleophiles such as amines and thiols.
This solid-phase synthetic strategy has the advantage of not
only facilitating purification but also of generating a library of
probes. Indeed, by attaching several lengths of linkers and cross
linking groups (azides and diazirines) to the resin, this protocol
would conceivably generate numerous probes. Further in-
vestigation on the development of solid-phase synthetic strate-
gies are underway in our labolatories.
7 (a) For a review of Ns chemistry, see: T. Kan and T. Fukuyama, J. Synth.
Org. Chem., Jpn., 2001, 59, 779; (b) T. Fukuyama, C.-K. Jow and M.
Cheung, Tetrahedron Lett., 1995, 36, 6373; (c) T. Fukuyama, M.
Cheung, C.-K. Jow, Y. Hidai and T. Kan, Tetrahedron Lett., 1997, 38,
5831; (d) T. Fukuyama, M. Cheung and T. Kan, Synlett, 1999, 1301.
8 For a review on secretases, see: M. S. Wolfe, J. Med. Chem., 2001, 44,
2039.
9 H. F. Dovey, V. John, J. P. Anderson, L. Z. Chen, P. de Saint Andrieu,
L. Y. Fang, S. B. Freedman, B. Folmer, E. Goldbach, E. J. Holsztynska,
K. L. Hu, K. L. Johnson-Wood, S. L. Kennedy, D. Kholodenko, J. E.
Knops, L. H. Latimer, M. Lee, Z. Liao, I. M. Lieberburg, R. N. Motter,
L. C. Mutter, J. Nietz, K. P. Quinn, K. L. Sacchi, P. A. Seubert, G. M.
Shopp, E. D. Thorsett, J. S. Tung, J. Wu, S. Yang, C. T. Yin, D. B.
Schenk, P. C. May, L. D. Altstiel, M. H. Bender, L. N. Boggs, T. C.
Britton, J. S. Clemens, D. L. Czilli, D. K. Dieckman-MacGinty, J. J.
Droste, K. S. Fuson, B. D. Gitter, P. A. Hyslop, E. M. Johnstone, W. Y.
Li, S. P. Little, T. E. Mabry, F. D. Miller and J. E. Audia, J. Neurochem.,
2001, 76, 173.
This work was partialy supported by 21st Century COE
Program.
Notes and references
†
Spectroscopic data for 11a–11c: 11a: 1H NMR (DMSO-d6, 400 MHz):
d 9.07 (br s, 1H), 8.40 (br s,1H), 7.77–7.75 (m, 4H), 7.68–7.63 (m, 4H), 6.45
(br s, 1H), 4.30–4.25 (m, 3H), 4.17–4.10 (m, 3H), 3.12–3.06 (m, 1H),
10 The determination of the structure of the DAPT derivatives and g-
secretase inhibition activity will be reported elsewhere.
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