Total Synthesis and Structure Revision of Palmarumycin B6

Total Synthesis, structure revision and antifungal activity of palmarumycin B8 and B7

Palmarymycins B8 (1), its regioisomer (2) and B7 (3) were synthesized via 10-, 9-, and 11-steps in 6.5 %, 2.3 % and 0.54 % overall yields from chroman-4-one (4), 4-hydroxyindanone (12), and 2,5-dimethoxybenzaldehyde (20) as the starting materials, using benzyl protection, enol trimethylsilyl ether by TMSOTf, Rubottom oxidation and deprotection with hydrogenation under Pd/C catalyst as the key steps, respectively. Their structures were characterized by 1H, 13C NMR, COSY, HSQC, HMBC and HR-ESI-MS spectral data. The structure of palmarumycin B8 was revised from 1 to 2 based on the total synthesis, 2D NMR analysis and DFT calculation. The antifungal assay results indicated that palmarumycin B8 (1) showed moderate inhibitory activity against Phytophthora capsica. Compounds 15 and 16 exhibited excellent in vitro antifungal activities against P. capsica with EC50 values of 2.17 and 8.50 μg/mL, respectively.

Enhancing Efficiency of Natural Product Structure Revision: Leveraging CASE and DFT over Total Synthesis

Natural products remain one of the major sources of coveted, biologically active compounds. Each isolated compound undergoes biological testing, and its structure is usually established using a set of spectroscopic techniques (NMR, MS, UV-IR, ECD, VCD, etc.). However, the number of erroneously determined structures remains noticeable. Structure revisions are very costly, as they usually require extensive use of spectroscopic data, computational chemistry, and total synthesis. The cost is particularly high when a biologically active compound is resynthesized and the product is inactive because its structure is wrong and remains unknown. In this paper, we propose using Computer-Assisted Structure Elucidation (CASE) and Density Functional Theory (DFT) methods as tools for preventive verification of the originally proposed structure, and elucidation of the correct structure if the original structure is deemed to be incorrect. We examined twelve real cases in which structure revisions of natural products were performed using total synthesis, and we showed that in each of these cases, time-consuming total synthesis could have been avoided if CASE and DFT had been applied. In all described cases, the correct structures were established within minutes of using the originally published NMR and MS data, which were sometimes incomplete or had typos.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Total synthesis, structure revision and cytotoxic activity of Sch 53825 and its derivatives

The first total synthesis of Sch 53825 (14) was achieved in 12 steps from 5-hydroxy-1-tetralone in 16% overall yield through N-benzyl cinchoninium chloride-catalyzed asymmetric epoxidation and a Mitsunobu reaction as the key steps. On this basis, the synthesis of palmarumycin B₆ was improved using the same raw material with 6 steps and 32% overall yield. Also, three new analogues with two chlorine atoms were synthesized. Their structures were characterized by ¹H, ¹³C NMR, HR-ESI-MS and X-ray diffraction data. The structure of natural Sch 53825 was revised as an epimer of compound 1 with the anti-hydroxy epoxide at C-4. Their cytotoxic activities against several tumor cell lines (HCT116, U251, BGC823, Huh-7 and PC9) showed that compound 11 exhibited excellent cytotoxicity against above mentioned cancer cell lines with IC₅₀ < 0.5 μM.

The first total synthesis of Sch 53825 (14) was achieved in 12 steps from 5-hydroxy-1-tetralone in 16% overall yield through N-benzyl cinchoninium chloride-catalyzed asymmetric epoxidation and a Mitsunobu reaction as the key steps.

One-pot synthesis of 1,3,5-triazine-2,4-dithione derivatives via three-component reactions

A catalyst-free one-pot synthetic methodology was developed for the preparation of 1,3,5-triazine-2,4-dithione derivatives through three-component reactions of arylaldehydes, thiourea, and orthoformates. The procedure tolerated a diverse range of arylaldehydes and orthoformates and provided a rapid entry to a variety of 4-aryl-6-(alkylthio)-3,4-dihydro-1,3,5-triazine-2(1H)-thiones (29 examples). The synthetic strategy relies on the dual role of thiourea in the cyclization with the aldehydes and the alkylation via an intermediate imidate formation. The structures of 1,3,5-triazine-2,4-dithione derivatives were characterized by spectroscopic techniques as well as by single crystal X-ray diffraction.

Total synthesis of Palmarumycin BGs, C1 and Guignardin E

The first total synthesis of Palmarumycin BG1–3, BG5–6, C₁ and Guignardin E (1–7) were achieved by the same intermediate Palmarumycin C₂ through a N-benzyl cinchoninium chloride-catalyzed epoxidation, an organoselenium-mediated reduction, and a cerium(iii) chloride hydrate-promoted regioselective ring-opening and elimination of cyclic α,β-epoxy ketone as the key steps via6–7 step routes using 1,8-dihydroxynaphthalene (DHN) and 5-methoxytetralone as the starting materials in overall yields of 1.0–17.4%, respectively. Their structures and absolute configurations were characterized and determined by ¹H, ¹³C NMR, IR, HR-ESI-MS and X-ray diffraction data. These compounds displayed significant inhibition activities against HCT116, U87-MG, HepG2, BGC823 and PC9 cell lines.

The first total syntheses of Palmarumycin BG1–3, BG5–6, C₁ and Guignardin E were achieved. These compounds displayed significant inhibition activities against HCT116, U87-MG, HepG2, BGC823 and PC9 cell lines.