G. Allegrone et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3528–3531
3531
current of 4.8 · 10À3 mA and heated capillary at 200 ꢁC.
The mass spectrometer operated in positive-ion mode,
with a scan range from m/z 100 to 500 (scan rate of 0.5
scan/s). APCI-MS/MS experiments in positive-ion mode
were performed by setting the collision energy at 32%
(optimized by using the LCQ–Xalibur software) on m/z
299 (M+HÀ32)+, using helium as collision gas. Retention
time of the impurity, the APCI/MS [m/z 299 (M+HÀ32)+],
and the APCI-MS/MS spectra were in agreement with
those of the structure assigned herein.
parameters were determined using 45 reflections in the
range 12.00ꢁ 6 2h 6 45.6ꢁ. A total of 4087 reflections
(3321 unique, Rint = 0.1095) were collected up to 136ꢁ in
2h and the index range: À1 6 h P 7, À8 6 k P 9 and
À25 6 l P 25. Three standard reflections, monitoring
every 100 reflections, showed no intensity decay. No
empirical adsorption correction was deemed necessary.
13. The structure was solved by a direct method using the
SIR97 program (Altomare, A.; Burla, M. C.; Camalli, M.;
Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Molit-
eni, A. G. G.; Polidori, G. P.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115), which revealed the position of
all non H-atoms. The refinement was carried out on F2 by
a full-matrix least-squares procedure with SHELXL97
(Sheldrick, G. M. SHELXL97. Release 97-2. Program for
the Refinement of Crystal Structures. (1997). University of
Go¨ttingen, Germany) for 273 parameters, with anisotropic
temperature factors for non-H atoms.
14. The site occupation factors converged to about 80% and
20% for the two positions, respectively. The final stage
converged to R = 0.0712 (Rw = 0.159) for 1509 observed
reflections, with I P 2r(I), and R = 0.163 (Rw = 0.208) for
3321 unique reflections after merging the equivalents. H
atoms, except for the carboxyl H atom, which was freely
refined with individual isotropic temperature factors, were
placed in geometrically calculated positions and refined in
a riding model.
10. The sample of the impurity 2 was dissolved in deuterated
chloroform, and the proton and carbon spectra were
acquired on a Bruker ARX 400 instrument at a temper-
ature of 305 K. The hydrogen and carbon chemical shifts
are referred to the signals of the solvent taken, respec-
tively, at 7.26 and 77.23 ppm from tetramethylsilane
(TMS). The coupling constants are expressed in Hz. The
assignment of the 1H and 13C NMR spectra was
performed by a comparison with the known spectra of
the parent compound tretinoin. 1H NMR of impurity 2: d
(ppm) 11.0 (1H, br s, COOH), 7.03 (1H, dd, J = 11.3 and
15.3 Hz, H–C(11)), 6.32 (1H, d, J = 15.3 Hz, H–C(12)),
6.25 (1H, d, J = 16.2 Hz, H–C(7) or H–C(8)), 6.17 (1H, d,
J = 16.2 Hz, H–C(8) or H–C(7)), 6.16 (1H, d, J = 11.3 Hz,
H–C(10)), 5.81 (1H, s, H–C(14)), 3.52 (1H, t, J = 4.3 Hz,
H–C(4)), 3.39 (3H, s, OCH3), 2.36 (3H, s, CH3C(13)), 2.00
(3H, s, CH3C(9)), 1.79 (3H, s, CH3–C(5)), 1.87–1.62 (3H,
m), 1.36 (1H, m), 1.03 (3H, s, CH3–C(1)), 1.02 (3H, s,
CH3C(1)). 13C NMR: d (ppm) 171.97 (COOH), 155.19
(C13), 142.37 (C6), 139.94 (C9), 129.41 (C5), 138.40 (C8),
135.63 (C12), 131.77 (C11), 130.30 (C10), 128.40 (C7),
118.19 (C14), 79.34 (C4), 56.88 (OCH3), 34.98 (C1), 34.92
(C2), 29.23 (C1), 27.67 (C1), 23.32 (C3), 19.08 (C5), 14.30
(C13), 13.11 (C9).
15. Malpezzi, L.; Fuganti, C.; Grasselli, P. Acta. Crystallogr.,
Sect. C 1997, 53, 508.
16. Malpezzi, L.; Boschetti, C.; Fuganti, C.; Grasselli, P.;
Magnone, G. A.; Pellegatta, C. Pharm. Ind. 1998, 60, 983.
17. Malpezzi, L.; Bruckner, S.; Ferro, D. R.; Luckhurst, G. R.
¨
Liq. Cryst. 2001, 28, 357.
18. Sawatzki, P.; Mikeska, T.; Nieger, M.; Bolte, M.; Kolter,
T. Acta Crystallogr., Sect. C 2003, 59, 225.
19. Newton, D. L.; Henderson, W. R.; Sporn, M. B. Cancer
Res. 1980, 40, 3413.
11. (a) Curley, R. W., Jr.; Carson, D. L. Bioorg. Med. Chem.
Lett. 1992, 2, 1133; (b) Rosenberg, M. J. Org. Chem. 1982,
47, 1698.
12. X-ray single crystal diffraction for molecular and crystal
structure determination. The crystal used in X-ray anal-
ysis, with approximate dimensions of 0.4 · 0.5 · 0.01 mm,
was obtained upon slow crystallisation from hexane.
Intensity data were collected, at room temperature, on a
Siemens P4 diffractometer with graphite monochromated
20. See for example Patel, J. B.; Huynh, C. K.; Handratta, V.
D.; Gediya, L. K.; Brodie, A. M. H.; Goloubeva, O. G.;
Clement, O. O.; Nanne, I. P.; Soprano, D. R.; Njar, V. C.
O. J. Med. Chem. 2004, 47, 6716.
21. Tanaka, H.; Kagechika, H.; Shudo, K. Chem. Pharm.
Bull. 1995, 43, 356.
˚
Cu-Ka radiation (k = 1.54179 A), using h/2h scan tech-
nique, voltage 40 kV and current 40 mA. Unit cell
22. Chen, Y.; Xiong, Z.; Yang, J.; Li, Y. J. Chem. Res., Synop.
1997, 472.