Highly Efficient and Mild Cascade Reactions Triggered by Bis(triphenyl)oxodiphosphonium Trifluoromethanesulfonate and a Concise Total Synthesis of Camptothecin

Phytochemical Analysis of Nothapodytes tomentosa and Distribution and Content of Camptothecin and its Analogues in Four Plants

Camptothecin (CPT) and its derivatives have attracted worldwide attention because of their notable anticancer activity. However, the growing demand for CPT in the global pharmaceutical industry has caused a severe shortage of CPT-producing plant resources. In this study, phytochemical analysis of Nothapodytes tomentosa results in the isolation and identification of CPT (13: ) and 16 analogues (1:  - 12, 14:  - 17: ), including a new (1: ) and five known (9, 10, 12, 15: , and 17: ) CPT analogues with an open E-ring. In view of the potential anticancer activity of CPT analogues with an open E-ring, the fragmentation pathways and mass spectra profiles of these six CPT analogues (1, 9, 10, 12, 15: , and 17: ) are investigated, providing a reference for the rapid detection of these compounds in other plants. Furthermore, based on the fragmentation patterns of CPT (13: ) and known analogues (2:  - 8, 11, 14, 16, 18:  - 26: ), the distribution and content of these compounds in different tissues of N. tomentosa, N. nimmoniana, Camptotheca acuminata, and Ophiorrhiza japonica are further studied. Our findings not only provide an alternative plant resource for further expanding the development and utilization of CPT and its analogues, but also lay a foundation for improving the utilization of known CPT-producing plant resources.

The Intramolecular Povarov Tool in the Construction of Fused Nitrogen-Containing Heterocycles

Nitrogen heterocycles are part of the structure of natural products and agents with important biological activity, such as antiviral, antibiotic, and antitumor drugs. For this reason, heterocyclic compounds are one of today's most desirable synthetic targets and the Povarov reaction is a powerful synthetic tool for the construction of highly functionalized heterocyclic systems. This process involves an aromatic amine, a carbonyl compound, and an olefin or acetylene to give rise to the formation of a nitrogen-containing heterocycle. This review illustrates advances in the synthetic aspects of the intramolecular Povarov reaction for the construction of intricate nitrogen-containing polyheterocyclic compounds. This original review presents research done in this field, with references to important works by internationally relevant research groups on this current topic, covering the literature from 1992 to 2022. The intramolecular Povarov reactions are described here according to the key processes involved, using different combinations of aromatic or heteroaromatic amines, and aliphatic, aromatic, or heteroaromatic aldehydes. Some catalytic reactions promoted by transition metals are detailed, as well as the oxidative Povarov reaction and some asymmetric intramolecular Povarov processes.

Recent advances in the synthesis of bridgehead (or ring-junction) nitrogen heterocycles via transition metal-catalyzed C–H bond activation and functionalization

An update on recent advances in the synthesis of bridgehead nitrogen fused heterocycles via transition metal-catalyzed C–H activation and functionalization is reported.

A concise and unexpected one-pot methodology for the synthesis of pyrazinone-fused pyridones

A post-Ugi/Michael/Retro-Michael reaction, aromatization and 5-exo-dig cyclization cascade reaction was developed and utilized for the synthesis of pyrazinone-fused pyridone derivatives under mild reaction conditions in one-pot.

Amino modified metal-organic frameworks as pH-responsive nanoplatforms for safe delivery of camptothecin

MIL-100(Fe) and MIL-101(Fe) metal-organic frameworks (MOFs) are excellent vehicles for drug delivery systems (DDSs) due to their high biocompatibility and stability in physiological fluids, as well as their pore diameter in the mesoporous range. Although they are appropriate for the internal diffusion of 20-(S)-camptothecin (CPT), a strongly cytotoxic molecule with excellent antitumor activity, no stable delivery system has been proposed so far for this drug based in MOFs. We here present novel DDSs based in amine functionalized MIL-100(Fe) and MIL-101(Fe) nanoMOFs with covalently bonded CPT. These CPT nanoplatforms are able to incorporate almost 20% of this molecule and show high stability at physiological pH, with no non-specific release. Based on their surface charge, some of these CPT loaded nanoMOFs present improved cell internalization in in vitro experiments. Moreover, a strong response to acid pH is observed, with up to four fold drug discharge at pH 5, which boost intracellular release by endosomolytic activity. These novel DDSs will help to achieve safe delivery of the very cytotoxic CPT, allowing to reduce the therapeutic dose and minimizing drug secondary effects.

Visible-Light-Induced Radical Cascade Cyclization: Synthesis of the ABCD Ring Cores of Camptothecins

A new strategy for constructing indolizino[1,2-b]quinolin-9(11H)-ones (ring cores of camptothecins) from readily available isocyanoarenes and N-(alkyl-2-yn-1-yl)pyridin-2(1H)-ones has been developed through a visible-light-induced radical cascade cyclization process. The reaction proceeds under mild conditions with fair to excellent yields. The easy introduction of substituents for both reactants and the broad functional group tolerance of the reaction make it a straightforward route to the cores of the marketed camptothecins and their derivatives.

Recent advances in the intramolecular Mannich reaction in natural products total synthesis

This review focuses on selected applications of the intramolecular Mannich reaction as a key step in the total synthesis of natural products (2000–2017).

Application of the aza-Diels–Alder reaction in the synthesis of natural products

The Diels–Alder reaction that involves a nitrogen atom in the diene or dienophile is termed the aza-Diels–Alder reaction.

Total Synthesis of Camptothecin and Related Natural Products by a Flexible Strategy

A flexible strategy for constructing natural products containing indolizinone or quinolizinone scaffolds and their analogues was developed, which was based on a cascade exo hydroamination followed by spontaneous lactamization. This method was applied in the total synthesis of camptothecin in nine steps in a new ring-forming approach. It was also used to efficiently prepare five biogenetically or structurally related natural alkaloids, including 22-hydroxyacuminatine, oxypalmatine, norketoyobyrine, naucleficine, and nauclefine, as well as 35 natural-product-like molecules. We believe that this method and the small-molecule library prepared with it can open new avenues for studying the bioactivity of camptothecin and Nauclea natural products.

Synthetic and Structural Studies of 2-Acylmethyl-6-R-Difunctionalized Pyridine Ligand-Containing Iron Complexes Related to [Fe]-Hydrogenase

As active site models of [Fe]-hydrogenase, tridentate 2-acylmethyl-6-methoxymethoxy-difunctionalized pyridine-containing complexes η(3)-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(L1) (4, L1 = I; 5, SCN; 6, PhCS2) were prepared via the following multistep reactions: (i) etherification of 2-MeO2C-6-HOC5H3N with ClCH2OMe to give 2-MeO2C-6-MeOCH2OC5H3N (1), (ii) reduction of 1 with NaBH4 to give 2-HOCH2-6-MeOCH2OC5H3N (2), (iii) esterification of 2 with 4-toluenesulfonyl chloride to give 2-TsOCH2-6-MeOCH2OC5H3N (3), (iv) nucleophilic substitution of 3 with Na2Fe(CO)4 followed by treatment of the resulting Fe(0) intermediate Na[(2-CH2-6-MeOCH2OC5H3N)Fe(CO)4] (M1) with I2 to give complex 4, and (v) condensation of 4 with KSCN and PhCS2K to give complexes 5 and 6, respectively. In contrast to the preparation of complexes 4-6, bidentate 2-acylmethyl-6-methoxymethoxy-difunctionalized pyridine-containing model complexes η(2)-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(I)(L2) (7, L2 = PPh3; 8, Cy-C6H11NC) and η(2)-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(L3) (9, L3 = 2-SC5H4N; 10, 8-SC9H6N) were prepared by ligand exchange reactions of 4 with PPh3, Cy-C6H11NC, 2-KSC5H4N, and 8-KSC9H6N, respectively. Particularly interesting is that the tridentate 2,6-bis(acylmethyl)pyridine- and 2-acylmethyl-6-arylthiomethylpyridine-containing model complexes η(3)-[2,6-(COCH2)2C5H3N]Fe(CO)2(L4) (11, L4 = PPh3; 12, CO) and η(3)-2-(COCH2-6-ArSCH2C5H3N)Fe(CO)2(ArS) (13, ArS = PhS; 14, 2-S-5-MeC4H2O) were obtained, unexpectedly, when 2,6-(TsOCH2)2C5H3N reacted with Na2Fe(CO)4 followed by treatment of the resulting mixture with ligands PPh3 and CO or disulfides (PhS)2 and (2-S-5-MeC4H2O)2. Reactions of ligand precursors 3 and 2,6-(TsOCH2)2C5H3N with Na2Fe(CO)4 were monitored by in situ IR spectroscopy, and the possible pathways for producing complexes 4 and 11-14 via intermediates Na[(2-CH2-6-MeOCH2OC5H3N)Fe(CO)4] (M1), Na[(2-CH2-6-TsOCH2C5H3N)Fe(CO)4] (M2), and (2-COCH2-6-CH2C5H3N)Fe(CO)3 (M3) are suggested. New compounds 1-14 were characterized by elemental analysis, spectroscopy, and, for some of them, X-ray crystallography.

Novel routes to quinoline derivatives from N-propargylamines

A walk around the new avenue to the synthesis of quinoline derivatives from N-propargylamines.

Practical synthesis of (20S)-10-(3-aminopropyloxy)-7-ethylcamptothecin, a water-soluble analogue of camptothecin

A robust, practical synthesis of (20S)-10-(3-aminopropyloxy)-7-ethylcamptothecin (T-2513, 5), which is a water-soluble analogue of camptothecin, has been developed. The key step in this synthesis is a highly diastereoselective ethylation at the C20 position by using N-arylsulfonyl-(R)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid ester as a chiral auxiliary, which affords the key intermediate ethyl-(S)-2-acyloxy-2-(6-cyano-5-oxo-1,2,3,5-tetrahydroindolizin-7-yl)butanoate (8k) in 93% yield and 87% de. Optically pure compound 8k was obtained by a single recrystallization from acetone and its further elaboration through Friedlander condensation afforded compound 5. This synthesis does not require any chromatographic purification steps and can provide compound 5 on a multi-gram scale in 6.3% overall yield (16 steps).

Electronic structure and photoionization and dissociation processes of bis(trifluoromethoxy)disulfurylperoxide, CF3OS(O)2OOS(O)2OCF3

In this work, we present a complete study of the photoionization and dissociation processes for bis(trifluoromethoxy)disulfurylperoxide, CF3OS(O)2OOS(O)2OCF3, which was generated by UV photolysis of a mixture of (CF3CO)2O, SO2, and O2 at a low temperature. The reaction product was detected and characterized by the photoelectron (PE) and photoionization mass spectroscopy (PIMS). For comparison, the geometric and electronic structures of CF3S(O)2OS(O)2CF3 (a), CF3OS(O)2OS(O)2OCF3 (b), and CF3OS(O)2OOS(O)2OCF3 (c) were investigated by the combination of experiments and theoretical studies. The PES results show that the outer electrons residing in nO(S=O) of b and c are more tightly bound than those of a. It is worthwhile mentioning that drastic changes occur in the geometry of c after one-electron ionization. The neutral molecule exhibits a gauche structure with the SOOS dihedral angle of 124.4 degrees . The first ionization process happens on the O-O antibonding orbital. The remarkable geometric changes between the ground-state molecule and cation are computed to be the gauche-to-trans rotation of deltaSOOS and the prolongation of the S1-O1 single bond length. According to the calculated bond dissociation energies, the dissociation process was discussed. The calculated results indicate that once the parent ion is formed, the dissociation of the S1-O1 bond to form CF3OSO2+ is inevitable.