9080 J. Phys. Chem. A, Vol. 107, No. 43, 2003
Bussotti et al.
1
thiocolchicine was obtained, mp 190 °C. H NMR (DMSO-d6,
δ): 8.66 (1 H, d, J ) 7 Hz), 7.26 (1 H, d, J ) 11 Hz), 7.12 (1
H, d, J ) 11 Hz), 7.00 (1 H, s), 6.78 (1 H, s), 4.33 (1 H, m),
3
.92 (3 H, s), 3.85 (3 H, s), 3.47 (3 H, s), 2.44 (3 H, s), 2.30 (1
H, m), 2.22 (1 H, m), 2.12 (1 H, m), 1.82 (1 H, m), 1.77 (3 H,
13
s). C NMR (DMSO-d6, δ): 181.0, 168.5, 157.5, 153.4, 151.5,
Figure 1. Colchicine (1) and thiocolchicine (5).
5) (Figure 1). Our data fit the hypothesis that photoisomeriza-
150.4, 141.0, 137.8, 134.3, 134.0, 128.0, 126.8, 126.0, 107.9,
6
1.2, 61.0, 55.9, 51.4, 35.5, 29.1, 22.3, 14.4.
(
Photochemical Reactions. Colchicine and thiocolchicine (10
tion occurs from the first singlet excited state. DFT and extended
multireference configuration interaction calculations are carried
out to reinforce such a hypothesis.
mg) were dissolved in methanol (10 mL) and irradiated for 1 h
with a 125-W high-pressure mercury arc lamp (Helios-Italquartz)
surrounded by a Pyrex water jacket. The solvent was evaporated,
and the crude product was chromatographed on silica gel.
Elution with acetone-CH2Cl2 2:8 gave the products. In the case
of colchicine, â- and γ-lumicolchicine were obtained. The
irradiation of thiocolchicine did not give products. â-Lumi-
Materials and Methods
Colchicine (1). The dark-brown gum (330 g) from the alcohol
extract of Colchicum seeds is diluted with 540 mL of water,
and the solution, which contains undissolved solid and resinous
material, is heated with 75 g of paraffin wax until the wax is
molten. The mixture is stirred vigorously and then allowed to
cool. The solid wax, which dissolves the resin, is lifted from
the surface, and the process is repeated twice with fresh wax.
The combined wax layers are extracted three times with 100
mL of boiling water, and the aqueous extracts are added to the
solution of the alkaloid. A paste of filter paper pulp (50 g)
1
colchicine: H NMR (CDCl3, δ): 6.66 (1 H, d, J ) 3 Hz),
6
.50 (1 H, s), 6.20 (1H, d, J ) 7 Hz), 4.82 (1 H, m), 4.09 (1 H,
dd, J1 ) J2 ) 3 Hz), 3.96 (3 H, s), 3.90 (3 H, s), 3.85 (3 H, s),
.70 (3 H, s), 3.60 (1 H, dd, J1 ) 3 Hz, J2 ) 2 Hz), 2.77 (2 H,
3
dd, J1 ) 15 Hz, J2 ) 9 Hz), 2.60 (1 H, dd, J1 ) 15 Hz, J2 )
1
3
9
1
1
Hz), 2.04 (3 H, s), 2.00 (1 H, m). C NMR (CDCl3, δ): 201.0,
70.1, 158.0, 153.0, 151.5, 145.4, 140.0, 138.5, 128.9, 117.5,
09.2, 61.7, 61.0, 56.8, 56.2, 51.6, 43.3, 32.5, 31.3, 23.5.
1
γ-Lumicolchicine: H NMR (CDCl3, δ): 6.65 (1 H, d, J ) 4
Hz), 6.50 (1 H, s), 6.05 (1H, d, J ) 8 Hz), 4.64 (1 H, dt, J1 )
(prepared by boiling filter paper with concentrated hydrochloric
acid to effect complete disintegration; the mass is then washed
with water until neutral) is then added to the aqueous colchicine
solution. The mixture is filtered on a filter bed, to which some
paper pulp has already been added, and yields a clear brown
solution. The filter bed is boiled with a little water and then
refiltered. The combined filtrates are extracted with 12 200-
mL portions of chloroform, with care being taken to ensure that
the chloroform is free from hydrochloric acid. The addition of
potassium carbonate to the yellow extract causes the precipita-
tion of some brown flocculent material, which is filtered from
the dried solution. The latter is evaporated, leaving a golden-
brown syrup. The syrup is redissolved in chloroform (150 mL),
and the solution is passed through a column of alumina,
previously saturated with benzene. Three bands are formeds
an upper, reddish-brown band; a larger, bright-yellow band; and
a lower, almost colorless band that contains colchicine. The
column is washed with chloroform until the yellowish eluate
becomes colorless and yields no residue on evaporation. The
distillation of chloroform out of the total eluate gives a golden-
yellow syrup, which is distilled three times with an equal volume
of absolute alcohol to remove the residual chloroform. The
residue is finally crystallized from ethyl acetate and yields 10
8
(
Hz, J2 ) 7 Hz), 4.03 (1 H, dd, J1 ) 4 Hz, J2 ) 3 Hz), 3.94
3 H, s), 3.87 (6 H, s), 3.70 (3 H, s), 3.60 (1 H, dd, J1 ) 3 Hz,
13
J2 ) 1 Hz), 2.66 (2 H, m), 2.00 (3 H, s), 1.96 (2 H, m).
C
NMR (CDCl3, δ): 198.9, 169.3, 157.5, 153.0, 151.5, 146.4,
1
5
40.5, 138.9, 138.4, 128.0, 118.0, 109.4, 61.3, 60.8, 56.8, 56.3,
0.4, 43.3, 49.1, 32.3, 30.9, 23.6.
Femtosecond Transient Spectroscopy. The experimental
instrumentation and data processing for femtosecond time-
resolved transient absorption (TA) spectroscopy have been
2
5-29
described in detail in previous papers.
Briefly, ultrashort pulses (duration ∼100 fs at 800 nm,
repetition rate 1 kHz, energy 700 µJ/pulse) are produced by a
Ti:sapphire-based laser system. The output of the amplifier is
divided into two portions. The most intense portion generates,
through the optical parametric process into a BBO crystal, signal
and idler output from 1.2-1.6 and 1.6-2.4 µm, respectively.
In the present experiment, the fourth harmonic of the signal
(1.38 µm) at 345 nm pumps the colchicine molecules directly
into the vibrational manifold of the S1 state. The weakest portion,
2 µJ/pulse, is focused onto a CaF2 plate and produces pulses of
2
6-29
a slightly chirped white-light continuum.
A portion of the
1
g of colchicine as fine colorless needles, mp 148-150 °C. H
continuum, from 350 to 700 nm, is selected after reflection onto
two broad band dielectric mirrors. The white beam is further
split into two parts of equal intensity by a 50/50 fused-silica-
Al beam splitter. One of these, acting as the probe beam,
spatially overlaps with the excitation beam and measures the
transient transmittance at any given delay time. The second
interacts with the sample in a different position and provides a
convenient reference signal. The intensity is detected by means
of a back-illuminated CCD camera with a spectral response in
the range of 300-1000 nm. Two horizontal strips covering 350
nm are selected on the CCD target to measure the probe and
reference intensities that are spectrally dispersed after passing
through a flat-field 25-cm Czerny-Turner spectrograph.
NMR (CDCl3, δ): 8.62 (1 H, d, J ) 6 Hz), 7.70 (1 H, s), 7.41
(
4
1 H, d, J ) 11 Hz), 6.91 (1 H, d, J ) 11 Hz), 6.54 (1 H, s),
.68 (1 H, dt, J1 ) 12 Hz, J2 ) 6 Hz), 4.04 (3 H, s), 3.95 (3 H,
s), 3.90 (3 H, s), 3.70 (3 H, s), 2.50 (2 H, m), 2.36 (1 H, m),
13
2
1
1
.02 (1 H, m), 1.96 (3 H, s). C NMR (CDCl3, δ): 179.0, 170.2,
64.3, 153.2, 152.8, 151.2, 141.3, 136.8, 136.0, 134.4, 130.4,
25.6, 113.4, 107.0, 61.5, 61.3, 56.5, 56.3, 53.2, 36.3, 29.2, 22.4.
Thiocolchicine (5). Colchicine (2.5 g) and PTSA (0.3 g) at
-80 °C were treated with cold CH3SH (15 g) in a sealed tube.
The mixture was warmed to -20 °C, and a yellow solution
was obtained. The mixture then became red. After several days
at -80 °C, CH3SH was distilled between 20 and 40 °C. The
residue was dissolved in a water-EtOAc mixture. The organic
phase was treated with NaHCO3 until neutrality was achieved.
The evaporation of the solvent gave 2.6 g of a brown gum.
After crystallization with 10 mL of EtOAc, 2.1 g (80%) of
The transient transmittance at a given delay time τ and
wavelength λ, T(τ, λ), is defined as I(τ, λ)/I0(λ), where I(τ, λ)
and I0(λ) are the intensities of the white-light continuum
component at λ reaching the detector having or having not