The Photochemical Behavior of Colchicone and Thiocolchicone

Bussotti, Laura; D’Auria, Maurizio; Foggi, Paolo; Lesma, Giordano; Righini, Roberto; Silvani, Alessandra

doi:10.1562/0031-8655(2000)071<0029:tpboca>2.0.co;2

Cited by 10 publications

(20 citation statements)

References 32 publications

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“…These results are in perfect agreement with those obtained in colchicone. 25 Our observation is also in agreement with previous results, indicating that the photochemical conversion of colchicine to lumicolchicines does not involve or only partially involves triplet transients.…”

Section: Resultssupporting

confidence: 93%

“…The experimental instrumentation and data processing for femtosecond timeresolved transient absorption (TA) spectroscopy have been described in detail in previous papers. [25][26][27][28][29] 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.…”

Section: Methodsmentioning

confidence: 99%

“…25,26 Mathematically, the measured relaxation kinetics are given by the following convolution integral:…”

Section: Methodsmentioning

confidence: 99%

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Photochemical Isomerization of Colchicine and Thiocolchicine

et al. 2003

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The photochemical reactivity of colchicine and thiocolchicine is described. Although the irradiation of colchicine gave a well-known transposition reaction to -and γ-lumicolchicines, thiocolchicine did not react. Femtosecond transient spectroscopy of colchicine showed a strong band with maximum at 510 nm appearing at τ ) 0. It disappeared within few hundred femtoseconds, leaving a broad structureless band with a maximum around 470 nm. A second band is observed around 410 nm. The analysis in time showed that the 510-nm component appeared instantaneously and decayed following a biexponential low with time constants of 300 ( 100 fs and 40 ps. The kinetics at 420 nm has a measurable rise time of 300 ( 150 fs. Quantum mechanical calculations on colchicine showed that this absorption is due to a S 1 f S 11 transition. In thiocolchicine, the instantaneous formation of a structure with maxima out of the investigated spectral region was observed. A strong absorption around 650 nm indicated the presence of a band with a maximum at longer wavelengths (> 700 nm) and a peak around 380 nm, which partially coincides with the ground-state absorption and therefore strongly affected by its bleaching. The instantaneous formation of an absorption around 650 nm and its rapid (∼500 fs) decay was observed. At shorter wavelengths (400 nm), the decay was fitted with a biexponential curve with the first time constant of about 80 ps. The second part of the decay had a very long tail up to 500 ps. Transient spectroscopy and configuration interaction calculations are in agreement with a mechanism involving a disrotatory cyclization of colchicine in its first excited singlet state. The lack of reactivity observed in thiocolchicine was explained by considering the presence of efficient ISC to the triplet state.Colchicine (1) is the major alkaloid of Colchicum autumnale (autumn crocus) and Gloriosa superba (flory lily), Liliacee. It is an ancient drug used in medicine for its antimitotic, antiinflammatory, and antineoplastic effects. 1,2 It has been used as a neurotoxin in animal models of Alzheimer's disease and epilepsy. 3 Several derivatives have been synthesized in order to improve antitumor activity. [4][5][6] The irradiation of colchicine leads to the formation of -and γ-lumicolchicine (3 and 4) (Scheme 1). Prolonged irradiation times lead to the formation of R-lumicolchicone (2) (Scheme 1). 7-21 -Lumicolchicine is a biologically active compound. 22 Previous photolysis studies indicated that the quantum yield of colchicine conversion depends on solvent polarity. 23 This behavior was explained by assuming the formation of a solvation complex in the ground state. The nature of the excited state responsible for the formation of photoproducts has not been determined; the authors proposed that colchicine isomerization occurs from the triplet excited state. However, in a subsequent study, they did not observe any quenching effect of several triplet acceptors on the reactivity. 24 In a previous paper, we found that transient absorption spectrosc...

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Section: Resultssupporting

confidence: 93%

Section: Methodsmentioning

confidence: 99%

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Photochemical Isomerization of Colchicine and Thiocolchicine

et al. 2003

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“…The occurrence of transport of lumicolchicines formed in the aerial part of the plant (flowers and leaves) to the corms and roots might also explain the presence of ␤-LC in these dark parts of the plants, although as noted above ␤-LC has been detected in the corms in the complete absence of light. Bussotti et al (31) recently reported that the non-nitrogen-containing 7-desacetamido-7-oxo-colchicine (colchicone), similar to colchicine photoisomerizes to ␤-lumicolchicone probably via its first excited singlet state.…”

Section: Discussionmentioning

confidence: 99%

Does the Photochemical Conversion of Colchicine into Lumicolchicines Involve Triplet Transients? A Solvent Dependence Study¶

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Quina

Moreira

et al. 2001

Photochem Photobiol

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beta- and gamma-lumicolchicines are photoproducts formed by the cycloisomerization of the tropolone ring of colchicine (COL) alkaloids. The mechanism of the photoconversion, suggested to involve the triplet state, is examined here by studying the effect of the solvent polarity on the lumicolchicine photoisomer ratio. Triplet COL, detected by laser flash photolysis, is quenched by oxygen, but not by transtilbene or 1-methylnaphtalene. Neither the quantum yield of conversion of COL nor the photoproduct ratio was altered by the presence of oxygen. Likewise, energy transfer to COL from triplet acetone produced by either isobutanal/horseradish peroxidase system or tetramethyldioxetane thermolysis failed to provoke photoreaction of COL. Our data argue against the intermediacy of a COL triplet state in the photoisomerization and stress on the role of specific solvent-solute interactions in determining the partitioning of excited singlet state into the beta- and gamma-isomer formation.

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“… 32 , 33 This is important from a clinical point of view, as considerable amounts of lumicolchicine were found in clear-glass ampules filled with colchicine for intravenous injections. 32 Studies on colchicine photoisomerization have been reported, 30 , 32 − 34 but the influence of different substituents on colchicine photosensitivity has not been investigated. It has been reported that the colchiceine (C10-demethylated colchicine analogue) undergoes photoisomerization similarly as colchicine, whereas thiocolchicine (C10-thiomethyl analogue) is resistant to UV irradiation.…”

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Photoinduced Skeletal Rearrangement of N-Substituted Colchicine Derivatives

et al. 2020

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Colchicine is an active pharmaceutical ingredient widely used for treating gout, pericarditis, and familial Mediterranean fever with high antimitotic activity. The photoisomerization of colchicine deactivates its anti-inflammatory and antimitotic properties. However, despite numerous reports on colchicine derivatives, their photostability has not been investigated in detail. This report reveals the effects of UV-induced rearrangement on the structure and reports the biological activity of new N -substituted colchicine derivatives.

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The Photochemical Behavior of Colchicone and Thiocolchicone

Cited by 10 publications

References 32 publications

Photochemical Isomerization of Colchicine and Thiocolchicine

Photochemical Isomerization of Colchicine and Thiocolchicine

Does the Photochemical Conversion of Colchicine into Lumicolchicines Involve Triplet Transients? A Solvent Dependence Study¶

Photoinduced Skeletal Rearrangement of N-Substituted Colchicine Derivatives

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