Antifungal activity against anthracnose-causing species of homopterocarpin derivatives

Derivatives of 3,9-dimethoxypterocarpan (1, homopterocarpin) were prepared by nitration, amination, and oxidation reactions, among others, and their antifungal activity was evaluated against the phytopathogenic fungi Colletotrichum gloeosporioides and C. lindemuthianum. Derivatives were purified by chromatographic techniques and identified by nuclear magnetic resonance spectroscopy. Eight derivatives were obtained from 1 corresponding to 3,9-dimethoxy-8-nitropterocarpan (2), 3,9-dimethoxy-2,8-dinitropterocarpan (3), 3,9-dimethoxy-2,8,10-trinitropterocarpan (4), 2,8-diamino-3,9-dimethoxypterocarpan (5), 3,9-dimethylcoumestan (6), medicarpin (7), 2'-hydroxy-4-(2-hydroxyethylsulfanyl)-7,4'-dimethoxyisoflavan (8), and 4-(2-hydroxyethylsulfanyl)-7,2',4'-trimethoxyisoflavan (9). The in vitro antifungal activity of the derivatives was determined at concentrations between 35 and 704 μM. Compounds 7 and 8 at 704 μM, showed an inhibition of radial growth and spore germination close to 100%, exceeding that found for the starting compound 1, which was 46%. Growth inhibition assays were also performed for the derivative 8 on papaya fruits (Carica papaya L. cv. Hawaiana) and mango (Mangifera indica L. cv. Hilacha) infected with C. gloeosporioides. Compound 8 showed fungal growth inhibition in fruits higher than that found for 1 and thymol (a recognized natural antifungal), under the same conditions. In general, derivatives that exhibited greater antifungal activity correspond to the compounds containing hydroxyl groups in the structure. Some of the compounds obtained could be considered promising for the control of phytopathogenic fungi.

Nickel-Catalyzed Dearomative Arylboration of Indoles: Regioselective Synthesis of C2- and C3-Borylated Indolines

Indole dearomatization is an important strategy to access indolines: a motif present in a variety of natural products and biologically active molecules. Herein, a method for transition-metal catalyzed regioselective dearomative arylboration of indoles to generate diverse indolines is presented. The method accomplishes intermolecular dearomatization of simple indoles through a migratory insertion pathway on substrates that lack activating or directing groups on the C2- or C3-positions. Synthetically useful C2- and C3-borylated indolines can be accessed through a simple change in N-protecting group in high regio- and diastereoselectivities (up to >40:1 rr and >40:1 dr) from readily available starting materials. Additionally, the origin of regioselectivity was explored experimentally and computationally to uncover the remarkable interplay between carbonyl orientation of the N-protecting group on indole, electronics of the C2-C3 π-bond, and sterics. The method enabled the first enantioselective synthesis of (-)-azamedicarpin.

Recent advances in palladium-catalyzed (hetero)annulation of C[double bond, length as m-dash]C bonds with ambiphilic organo(pseudo)halides

Palladium has proven to be effective in catalyzing the (hetero)annulation of C[double bond, length as m-dash]C bonds with ambiphilic organo(pseudo)halides. Through the employment of appropriate ambiphilic coupling partners, efficient annulation of a variety of allenes, 1,3-dienes, strained alkenes, styrenes, and other C[double bond, length as m-dash]C bond variants can be achieved to provide direct access to numerous useful hetero- and carbocyclic scaffolds. In this Feature Article, we summarize palladium-catalyzed (hetero)annulation methods reported since 2005 (spanning just over 15 years) and discuss outstanding challenges in this area of study.

Synthesis and antiproliferative activity of 6-naphthylpterocarpans

The Heck-oxyarylation of racemic 2-(1-naphthyl)- and 2-(2-naphthyl)-2H-chromene derivatives were carried out resulting diastereoselectively in (6S*,6aR*,11aR*)-6-(1-naphthyl)- and 6-(2-naphthyl)-pterocarpans as major products and bridged (6R*,12R*)-6,12-methanodibenzo[d,g][1,3]dioxocine derivatives as minor products. Antiproliferative activity of two 6-naphthylpterocarpans was identified by MTT assay against A2780 and WM35 human cancer cell lines with low micromolar IC50 values. The measured 0.80 and 3.51 μM IC50 values of the (6S*,6aR*,11aR*)-6-(1-naphthyl)pterocarpan derivative with 8,9-methylenedioxy substitution represent the best activities in the pterocarpan family. Enantiomers of the pterocarpan and dioxocine derivatives and their chiral 2-naphthylchroman-4-one and 2-naphthyl-2H-chromene precursors were separated by HPLC using chiral stationary phase. HPLC-ECD spectra were recorded and absolute configuration and low-energy solution conformations were determined by TDDFT-ECD calculations. Characteristic ECD transitions of the separated enantiomers were correlated with their absolute configuration.