Solvent Effects on the Valence UV−Vis Absorption Spectra of Topotecan Anticancer Drug in Aqueous Solution at Room Temperature: A Nanoseconds Time-Scale TD-DFT/MD Computational Study

Theoretical study on the solvation mechanism of camptothecin in ionic liquids

To reduce the environmental pollution caused by organic solvents and improve the extraction efficiency, a range of imidazolium-based ionic liquid (IL) combinations of [Omim]⁺ paired with [Br]^-, [BF₄]^-, [Cl]^-, [ClO₄]^-, [HsO₄]^-, [NO₃]^-, [NTf₂]^-, [OAc]^-, [PF₆]^-, and [TsO]^- are explored for the extraction of camptothecin (CPT) using molecular dynamics (MD) simulation and density functional theory (DFT) calculations. It is found that the ILs containing [Br]^-, [OAc]^-, and [TsO]^- anions are the most promising solvents for CPT solvation because they exhibit stronger interaction energy and the lowest self-diffusion coefficient of CPT among all ILs. The microscopic mechanism at the molecular level is revealed based on DFT calculations and MD simulations, and the results demonstrate that the IL (i.e., [Omim][TsO]) containing anions with strong hydrogen bond (HB) acceptability and aromatic ring structure corresponds to both the strongest van der Waals interaction and strongest HB interaction of CPT-anions. Therefore, it is recommended that anions with aromatic ring structures or strong HB acceptability are promising anion candidates, while anions containing electron withdrawing groups and bulky substituents should be avoided. This work provides intermolecular insight into designing and selecting effective ILs for natural insoluble active pharmaceutical ingredient dissolution and extraction in further research.

Synthesis, Experimental and Density Functional Theory (DFT) Studies on Solubility of Camptothecin Derivatives

Two camptothecin derivatives, 10-cyclohexyl-7-methyl-20(S)-camptothecin and 7-methyl-10-morpholino-20(S)-camptothecin, were synthesized and their differences in solubility were investigated using four chosen solvent systems. Based on our results, 10-cyclohexyl-7-methyl-20(S)-camptothecin exhibited higher solubilities than 7-methyl-10-morpholino-20(S)-camptothecin in polar aprotic solvents. However, these two camptothecin derivatives did not exhibit apparent differences in solubility between 5% dimethyl sulfoxide (DMSO)/95% normal saline co-solvent system and 5% dimethylacetamide (DMAC)/95% normal saline co-solvent system. To rationalize their differences in solubility, we also tried to perform a DFT-B3LYP study to investigate their interaction with one water molecule.

Quantum chemical calculation of free radical substitution reaction mechanism of camptothecin

Free radical substitution reaction, which has low energy barrier and takes place in mild reaction conditions, is an important method for camptothecin's modification. The experimental data show that the free radical substitution reaction of camptothecin has high site selectivity, and prefers to take place at site 7. Up to now, few researches focus on the mechanism of it. In this study, the differences of the reaction rate constant (k) for the reactions at different sites, such as site of 7, 9, 10, 11, 12, were investigated with B3LYP of density functional theory at the 6-31 + G (d, p) base set level and CPCM aqueous solvent model. It was found that the substitution reaction can be carried out in two steps in acidic condition. First, the methyl radical attacks the corresponding site to form an intermediate having methyl radical combined with the camptothecin skeleton, and then a hydrogen atom was abstracted by the singlet oxygen to form methyl camptothecin, wherein the first step was the rate control step of the reaction. The results show that site 7 has the higherreaction rate constant (k) than other examined sites, indicating that the reaction tends to take place on site 7 position, which is in agreement with the experimental results.

Silicon-containing analogs of camptothecin as anticancer agents

The plant pentacyclic alkaloid camptothecin and its structural analogs were extensively studied. These compounds are interesting due to the antitumor activity associated with their ability to inhibit topoisomerase I in tumor cells. During the last decades of the 20th century, a large number of the silicon-containing camptothecins (silatecans) were synthesized. 7-tert-Butyldimethylsilyl-10-hydroxy-camptothecin (DB-67 or AR-67) has enhanced lipophilicity and demonstrates a antitumor activity superior to its carbon analog. To date, certain silatecans are under clinical trials and their ultimate role in cancer therapy appears promising. In this review, we present chemical methodologies for the synthesis of silicon-containing camptothecins, their chemical properties, biological activity, and results of clinical trials.

DOSY NMR and MALDI-TOF evidence of covalent binding the DNA duplex by trimethylammonium salts of topotecan upon near UV irradiation

Using DOSY NMR and MALDI-TOF MS techniques, we present evidence that quaternary trimethylammonium salts of topotecan, [TPT-NMe3 ](+) X(-) (X = CF3SO3, HCOO), bind covalently the natural DNA oligomer upon near UV irradiation in water under physiological conditions. It is shown that formate salt is very reactive at pH 7 and requires short irradiation time. This weak irradiation at 365 nm paves the way for a new application of TPT derivatives in clinical use, which can dramatically increase the therapeutic effects of a medicine.

Solvent dependency of the UV-Vis spectrum of indenoisoquinolines: role of keto-oxygens as polarity interaction probes

Indenoisoquinolines are the most promising non-campthotecins topoisomerase IB inhibitors. We present an integrated experimental/computational investigation of the UV-Vis spectra of the IQNs parental compound (NSC314622) and two of its derivatives (NSC724998 and NSC725776) currently undergoing Phase I clinical trials. In all the three compounds a similar dependence of the relative absorption intensities at 270 nm and 290 nm on solvent polarity is found. The keto-oxygens in positions 5 and 11 of the molecular scaffold of the molecule are the principal chromophores involved in this dependence. Protic interactions on these sites are also found to give rise to absorptions at wavelength <250 nm observed in water solution, due to the stabilization of highly polarized tautomers of the molecule. These results suggest that the keto-oxygens are important polarizable groups that can act as useful interactors with the molecular receptor, providing at the same time an useful fingerprint for the monitoring of the drug binding to topoisomerase IB.