Synthesis and stereochemical determination of an antiparasitic pseudo-aminal type monoterpene indole alkaloid

5-Nor stemmadenine alkaloids, isolated from the genus Tabernaemontana, display a range of bioactivity. 16-Hydroxy-16,22-dihydroapparicine, the active component of an extract from the Tabernaemontana sp. (dichotoma, elegans, and divaricate), exhibited potent antimalarial activity, representing the first such report of the antimalarial property of 5-nor stemmadenine alkaloids. We, therefore, decided to attempt the total synthesis of the compound to explore its antimalarial activity and investigate structure and bioactivity relationships. As a result, we completed the first total synthesis of 16-hydroxy-16,22-dihydroapparicine, by combining a phosphine-mediated cascade reaction, diastereoselective nucleophilic addition of 2-acylindole or methylketone via a Felkin-Anh transition state, and chirality transferring intramolecular Michael addition. We also clarified the absolute stereochemistries of the compound. Furthermore, we evaluated the activity of the synthetic compound, as well as that of some intermediates, all of which showed weak activity against chloroquine-resistant Plasmodium falciparum (K1 strain) malaria parasites.

Aerobic oxidation of indole carbinols using Fe(NO3)3·9H2O/TEMPO/NaCl as catalysts

A practical aerobic oxidation of indole carbinols using Fe(NO3)3·9H2O/TEMPO/NaCl in DCE at room temperature and atmospheric pressure of oxygen affording aldehydes or ketones in good to excellent yields was developed. Furthermore, when using the industrially favored solvent toluene instead of DCE and air instead of pure oxygen, this protocol also works smoothly, demonstrating its high potential for possible industrial application.

Synthesis of indole analogues of the natural schweinfurthins

An interest in the schweinfurthins, natural stilbenes with significant antiproliferative activity, has prompted efforts to prepare a set of indole analogues. To approach the desired compounds through a Horner-Wadsworth-Emmons condensation, new indole derivatives bearing a phosphonomethyl substituent in the B-ring were required. The parent indole system with the necessary substitution pattern was obtained through Stobbe condensation and cyclization. A prenyl substituent was incorporated at the C3 position of a 4,6-disubstituted indole through a highly regioselective electrophilic aromatic substitution reaction, while metalation and alkylation provided the C2-prenylated indole. After introduction of the phosphonate group through classical reactions, the new indole phosphonates were found to undergo the desired condensation with nonracemic aldehydes representing the schweinfurthin left half. This approach provides facile access to new heteroaromatic analogues of the natural schweinfurthins and should be applicable to many other natural stilbenes as well.

Carbocyclization versus oxycyclization on the metal-catalyzed reactions of oxyallenyl C3-linked indoles

The preparation of previously unknown (indol-3-yl)-α-allenols and -allenones was accomplished from indole-3-carbaldehydes, through indium-mediated Barbier allenylation reaction taking advantage of the N-(2-pyridyl)sulfonyl group. Metal-catalyzed cyclizations of oxyallenyl C3-linked indoles proceeded in two ways depending on the presence or absence of the N-(2-pyridyl)sulfonyl group. For allenols, gold-catalyzed oxycyclization occurred in the presence of the protecting group; in the absence of the protecting group, palladium- and gold-catalyzed benzannulations operated. On the contrary, under gold catalysis furyl-indoles were obtained as exclusive products from NH-allenones, while 5-endo carbocyclization adducts were the major components starting from N-SO2py-protected allenones. These cyclization reactions have been developed experimentally, and their mechanisms have additionally been investigated by a computational study.

Enhancement of chemically-induced HL-60 cell differentiation by 3,3'-diindolylmethane derivatives

3,3'-Diindolylmethane (DIM, 1) and its derivatives have been prepared, and their enhancing effects on chemically-induced HL-60 cell differentiation were analyzed. Among the prepared compounds, IndDIM (12) showed the most potent enhancing effect on HL-60 cell differentiation induced by chemicals, including retinoids, 1,25-dihydroxyvitamin D(3), 12-O-tetradecanoyl phorbol-13-acetate and dimethyl sulfoxide.