Photochemical Isomerization of Colchicine and Thiocolchicine

Photolysis and cytotoxicity of the potentially toxic composition of daylily flower: colchicine

The photolysis of colchicine under ultraviolet and visible light irradiation was studied by ultraviolet (UV) scanning and HPLC-MS. The photoproduct was proposed and the cytotoxicity change before and after irradiation was investigated. Results showed that both ultraviolet and visible light irradiation could effectively degrade colchicine into deacetamido-lumicolchicine. The process conformed to first-order kinetics, in which a high degradation rate (K = 0.5862 h^− 1) was observed when colchicine was dissolved in ethanol and irradiated by UV light. Cell viability and cell cycle studies proved that a photolysis treatment of colchicine could weaken the cytotoxicity effectively. Colchicine inhibited the division of BRL 3 A cells in G2/M phase with an IC₅₀ value of 0.48 µg/mL, while the toxic effect could be reduced significantly with IC₅₀ 2.1 µg/mL when colchicine was exposed to UV irradiation. Results are beneficial to the toxicity elimination of colchicine in the processing of daylily flower in food industry, and can also provide photochemistry reference for colchicine-related studies.

Photoinduced Skeletal Rearrangement of N-Substituted Colchicine Derivatives

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.

Synthesis, biological evaluation and molecular docking studies of new amides of 4-bromothiocolchicine as anticancer agents

Colchicine is the major alkaloid isolated from the plant Colchicum autumnale, which shows strong therapeutic effects towards different types of cancer. However, due to the toxicity of colchicine towards normal cells its application is limited. To address this issue we synthesized a series of seven triple-modified 4-bromothiocolchicine analogues with amide moieties. These novel derivatives were active in the nanomolar range against several different cancer cell lines and primary acute lymphoblastic leukemia cells, specifically compounds: 5-9 against primary ALL-5 (IC₅₀ = 5.3-14 nM), 5, 7-9 against A549 (IC₅₀ = 10 nM), 5, 7-9 against MCF-7 (IC₅₀ = 11 nM), 5-9 against LoVo (IC₅₀ = 7-12 nM), and 5, 7-9 against LoVo/DX (IC₅₀ = 48-87 nM). These IC₅₀ values were lower than those obtained for unmodified colchicine and common anticancer drugs such as doxorubicin and cisplatin. Further studies revealed that colchicine and selected analogues induced characteristics of apoptotic cell death but manifested their effects in different phases of the cell cycle in MCF-7 versus ALL-5 cells. Specifically, while colchicine and the studied derivatives arrested MCF-7 cells in mitosis, very little mitotically arrested ALL-5 cells were observed, suggesting effects were manifest instead in interphase. We also developed an in silico model of the mode of binding of these compounds to their primary target, β-tubulin. We conducted a correlation analysis (linear regression) between the calculated binding energies of colchicine derivatives and their anti-proliferative activity, and determined that the obtained correlation coefficients strongly depend on the type of cells used.

Theoretical Study of the Photochemical Isomerization of Colchicine

The photochemical reaction of colchicine to β- and γ-lumicolchicine, through a mechanism involving a disrotatory cyclization, is studied by theoretical methods. The energetics of the reaction, including one or two methanol solvent molecules, are studied at the DFT-B3LYP and multireference perturbation levels of theory using the 6-31G(d) basis set. The results show that, in agreement with experimental results, the first excited state of colchicine at ∼3.6 eV can lead to both β- and γ-lumicolchicine, whose energy is about 15 kcal mol(-)(1) above the colchicine energy. Owing to the high steric tension of the condensed four- and five-atom rings arising from cyclization, the two trans-lumicolchicines are higher in energy (>60 kcal mol(-)(1)), and their formation appears much less probable. A partial inclusion of the solvent effects through the addition of two solvent molecules does not alter the general conclusions based on the free energy in the gas phase. The photochemical reaction path is studied by choosing the distance between the two carbon atoms which form the new σ bond as the leading coordinate of the minimum-energy path of both the ground and the first singlet excited states. The energies are computed by Multi Configurational self-consistent-field calculations on a model molecule, retaining those atoms that presumably play an active role in the reaction. A reasonable mechanism starting from colchicine in the first singlet excited state and leading to γ-lumicolchicine is proposed. On the contrary, a high-energy transition state is found for trans-lumicolchicines, whose formation, although not strictly forbidden for energetic reasons, appears to be rather improbable.

Study of Mechanisms of Light-Induced Dissociation of Ru(dcbpy)(CO)2I2 in Solution down to 20 fs Time Resolution

Mechanisms of the light-induced ligand exchange reaction of (trans-I) Ru(dcbpy)(CO)2I2 (dcbpy = 4,4'-dicarboxylic acid-2,2'-bipyridine) in ethanol have been studied by transient absorption spectroscopy. Ultraviolet 20 fs excitation pulses centered at 325 nm were used to populate a vibrationally hot excited pi bipyridyl state of the reactant that quickly relaxes to a dissociative Ru-I state resulting in the release of one of the carbonyl groups. Quantum yield measurements have indicated that about 40% of the initially exited reactant molecules form the final photoproduct. A 62 fs rise component in the transient absorption (TA) signal was observed at all probe wavelengths in the visible region for the ongoing reaction, while the rise for the photoproduct was pulse limited (20 fs). We assign the observed 62 fs time component to the depopulation of the repulsive CO dissociative state. Vibrational coherences of the TA signals were observed at a wavenumber of 90 cm(-1). The resolved frequency, typical of I-Ru-I vibrational modes, is assigned to trans-cis isomerization of the iodines of the five-coordinated intermediate and damping of this oscillation in 500 fs to simultaneous solvent coordination. Cooling of the hot reactant and the product molecules occurs on a much slower time scale from 4 to 270 ps (Lehtovuori, V.; Aumanen, J.; Myllyperkiö, P.; Rini, M.; Nibbering, E. T. J.; Korppi-Tommola, J. J. Phys. Chem. A 2004, 108, 1644).

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain as isoquinoline system, together with napthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids with the structures of new bases, together with their reactions and syntheses, are reported. The literature from July 2003 to June 2004 is reviewed, with 145 references cited.