Total syntheses of (+/-)-preussomerins G and I

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.

Hemithioindigo-Based Trioxobicyclononadiene: 3D Multiswitching of Electronic and Geometric Properties

Molecular photoswitches that offer simultaneous precise control over geometrical and electronic changes are rare yet highly sought tools for the development of responsive nanosystems. Here we present such an advantageous combination of property control within a novel multiphotoswitch architecture. Hemithioindigo-based trioxobicyclononadiene (HTI-TOND) offers a rigid three-dimensional molecular structure that undergoes different exotic rearrangement reactions upon photochemical and thermal signaling. Three to four different states with distinct geometric and electronic properties can be accessed reversibly in high yields within this molecular framework. Thus, a highly promising and unique switching tool has become available to instill the next level of addressability at the smallest scales.

Formal dual C(sp2)–H cross-dehydrogenative C–O bond formation to construct highly functionalized diaryl ethers with O2

A formal dual C(sp2)–H cross-dehydrogenative C–O bond formation reaction between phenols and naphthylamine derivatives to construct diaryl ethers has been developed under mild conditions.

Total Synthesis of (±)-Spiroaxillarone A

Spiroaxillarone A, a novel and unique spirocyclic dinaphthalene natural product with significant antimalarial activity, was regioselectively synthesized from tetrahydrocurcumin in five steps with an overall 10% yield. Key features of the synthesis involved an oxidized free radical cycloaddition to build the spiro ring central skeleton and an oxidized dehydrogenation to introduce two double bonds via enol silicon ether from diketones.

Light/inductive effect induced isomerization of chromeno-5-methyl-2,6,9-trioxabicyclo[3.3.1]nonadienes

An efficient rearrangement of coumarin-based trioxabicycles and the effect of UV light and electron-withdrawing substituents on this transformation are reported.

Total Synthesis and Antifungal Activity of Palmarumycin CP17 and Its Methoxy Analogues

Total synthesis of naturally occurring spirobisnaphthalene palmarumycin CP₁₇ and its methoxy analogues was first achieved through Friedel-Crafts acylation, Wolff-Kishner reduction, intramolecular cyclization, ketalization, benzylic oxidation, and demethylation using the inexpensive and readily available methoxybenzene, 1,2-dimethoxybenzene and 1,4-dimethoxybenzene and 1,8-dihydroxynaphthalene as raw materials. Demethylation with (CH₃)₃SiI at ambient temperature resulted in ring A aromatization and acetal cleavage to give rise to binaphthyl ethers. The antifungal activities of these spirobisnaphthalene derivatives were evaluated, and the results revealed that 5 and 9b exhibit EC₅₀ values of 9.34 µg/mL and 12.35 µg/mL, respectively, against P. piricola.

A versatile, non-biomimetic route to the preussomerins: syntheses of (+/-)-preussomerins F, K and L

The first total syntheses of the title fungal metabolites preussomerins F, K and L are described and their structures confirmed thereby. The syntheses were achieved following a versatile, unified, non-biomimetic approach, which is easily extendable to prepare other known and novel members of this family. Key steps include the functionalisation of a 2-arylacetal anion, tandem one-pot Friedel-Crafts cyclisation-deprotection, regioselective substrate-directable hydrogenation and reductive-opening of epoxides.

Unified route to the palmarumycin and preussomerin natural products. Enantioselective synthesis of (-)-preussomerin G

The total syntheses of eight members of the palmarumycin family have been achieved, with identification of the absolute stereochemistry for three of these natural products. In addition, the ras-farnesyl transferase inhibitor (-)-preussomerin G has been synthesized, achieving the first enantioselective route for accessing this family of natural products. Highlights of the synthetic work include an asymmetric epoxidation of a cyclic enone in excellent yield and enantiomeric excess and a potentially biomimetic oxidative spirocyclization for the introduction of the bis-spiroketal array unique to the preussomerin natural products.

Synthesis of cis- and trans-5,8-dihydroxy-5,6,7,8-tetrahydro-1,4-naphthoquinone

Cis- and trans-5,8-dihydroxy-5,6,7,8-tetrahydro-1,4-naphthoquinone (1a, 1b) were for the first time synthesized from 5,8-dihydroxy-1,4-naphthoquinone (naphthazazine) (6) as a starting material and racemic triol (3) was first synthesized from 7. The configuration of 1a was determined by X-ray analysis.

Formal total synthesis of (+)-diepoxin sigma

The highly oxygenated antifungal anticancer natural product (+/-)-diepoxin sigma was prepared in 10 steps and in 15% overall yield from O-methylnaphthazarin. Highlights of the synthetic work include an Ullmann coupling and a possibly biomimetic oxidative spirocyclization for the introduction of the naphthalene ketal as well as the use of a retro-Diels-Alder reaction to unmask the reactive enone moiety in the naphthoquinone bisepoxide ring system. A novel highly bulky chiral binaphthol ligand was developed for a boron-mediated Diels-Alder reaction that constitutes a formal asymmetric total synthesis of (+)-diepoxin sigma.