An Efficient and General Route to gem-Difluoromethylenated α,β-Unsaturated δ-Lactones: High Enantioselective Synthesis of gem-Difluoromethylenated Goniothalamins

Goniothalamin-Related Styryl Lactones: Isolation, Synthesis, Biological Activity and Mode of Action

This review covers the chemistry and biological aspects of goniothalamin-related styryl lactones isolated from natural sources. This family of secondary metabolites has been reported to display diverse uses in folk medicine, but only a limited number of these compounds have been throughly investigated regarding their biological profile. Herein, we cover the goniothalamin-related styryl lactones having a C6-C3-C4 framework which appeared in the literature for the first time in the period 2000-2017, and the reports on the synthesis, biological activity and mechanism of action which were published from 2007-2017.

Synthesis of novel 13α-estrone derivatives by Sonogashira coupling as potential 17β-HSD1 inhibitors

Novel 13α-estrone derivatives were synthesized by Sonogashira coupling. Transformations of 2- or 4-iodo regioisomers of 13α-estrone and its 3-methyl ether were carried out under different conditions in a microwave reactor. The 2-iodo isomers were reacted with para-substituted phenylacetylenes using Pd(PPh₃)₄ as catalyst and CuI as a cocatalyst. Coupling reactions of 4-iodo derivatives could be achieved by changing the catalyst to Pd(PPh₃)₂Cl₂. The product phenethynyl derivatives were partially or fully saturated. Compounds bearing a phenolic OH group furnished benzofurans under the conditions used for the partial saturation. The inhibitory effects of the compounds on human placental 17β-hydroxysteroid dehydrogenase type 1 isozyme (17β-HSD1) were investigated by an in vitro radiosubstrate incubation method. Certain 3-hydroxy-2-phenethynyl or -phenethyl derivatives proved to be potent 17β-HSD1 inhibitors, displaying submicromolar IC₅₀ values.

Hydrogen bonding-promoted efficient Ru-catalyzed ring-closing metathesis of demanding homoallyl 2-(hydroxymethyl)acrylates

An efficient hydrogen bonding-guided ring-closing metathesis (RCM) reaction of sterically demanding homoallyl 2-(hydroxymethyl)acrylates catalyzed by the Hoveyda-Grubbs 2nd generation catalyst was developed and the reaction mechanism was explored. Adding a substituent to the hydroxymethyl group in this scaffold resulted in a class of challenging RCM substrates, although usable yields could be obtained. However, substrates bearing a 1-oxygenated alkyl group on the homoallylic carbon gave excellent RCM yields, providing a practical solution. Experimental and computational evidence indicated an unusual directing effect of OHCl hydrogen bonding between the substrate and Ru catalyst, which guides Ru to interact with the electron-deficient, more hindered acrylic C[double bond, length as m-dash]C bond and thus triggers the RCM process.

Synthesis of 5,6-Dihydro-α-Pyrone via Ring-Closing Metathesis and Intramolecular Horner–Wadsworth–Emmons Reactions

Ring-closing metathesis (RCM) and intramolecular Horner–Wadsworth–Emmons (HWE) reactions were assessed for synthesis of cis-5-methyl-6-phenylethyl-5,6-dihydro-α-pyrone. The RCM reaction employing Grubbs’ second generation catalyst afforded a 96% yield at 80 °C in toluene. The HWE reaction under modified Masamune–Roush conditions delivered only 23% yield due to a competitive elimination reaction.

Synthesis of gem-difluoromethylenated analogues of boronolide

The straightforward synthesis of four gem-difluoromethylenated analogues 4–7 of boronolide is described. The key steps of the synthesis include the concise preparation of the key intermediates 12a–b through the indium-mediated gem-difluoropropargylation of aldehyde 9 with the fluorine-containing building block 11 and the efficient construction of α,β-unsaturated-δ-lactones 15a–b via BAIB/TEMPO-procedure.

Synthesis and cytotoxic activity of fluorinated analogues of Goniothalamus lactones. Impact of fluorine on oxidative processes

Novel fluorinated analogues of goniothalamin 1 and howiinol A 2 have been prepared from trifluorocrotonate derivatives. Trifluoromethyl goniothalamin (R/S) 4 showed a slightly lower activity than 1, while the trifluoromethyl howiinol A 16 exhibited similar activities on several cell lines in the micromolar range. Unlike (R) goniothalamin and howiinol A, trifluoromethyl parent compounds remained unchanged when submitted to biomimetic oxidative systems.

(S)-6-{[(S)-2,2-Dimethyl-1,3-dioxolan-4-yl]meth-yl}-5,5-difluoro-5,6-dihydro-2H-pyran-2-one

The title compound, C₁₁H₁₄F₂O₄, is a γ,γ-gem-difluorinated α,β-unsaturated δ-lactone. The dioxolane five-membered ring and the lactone ring adopt half-chair conformations. There are two inter­molecular C—H⋯O inter­actions involving the carbonyl group as an acceptor which stabilize the crystal structure.