Asymmetric Total Synthesis of the Putative Structure of Diplopyrone

Total Synthesis and Determination of Absolute Configuration of Cryptorigidifoliol G

The first asymmetric total synthesis of (1S,5R,7S)-cryptorigidifoliol G and (1S,5R,7R)-cryptorigidifoliol G of the proposed natural product was achieved. The key steps in the synthesis involved Keck-Maruoka allylation, our own developed protocol for the construction of the trans-2,6-disubstituted dihydropyran, iodolactonization, cross-metathesis, Prins cyclization, and cis-Wittig olefination reaction. A comparison of the NMR as well as analytical data and thorough analysis of the 2D NMR suggested that the absolute stereochemistry of the proposed natural product is (1S,5R,7S)-cryptorigidifoliol G.

Total synthesis and cytotoxic activity of 7-O-methylnigrosporolide and pestalotioprolide D

A convergent total synthesis of 7-O-methylnigrosporolide and pestalotioprolide D has been accomplished in 17 longest linear steps starting with 1.7% and 2.6% overall yields, respectively, starting from (S)-propylene oxide and known (S)-benzyl glycidyl ether. Our synthesis exploited acetylide addition and Shiina macrolactonization to assemble the macrocycle, Lindlar reduction, Wittig and Still–Gennari olefination to construct the three olefins as well as a Jacobsen hydrolytic kinetic resolution to install the stereogenic center. The selection of silyl protecting group of C-4 alcohol was crucial for final deprotection step. Our synthesis also led to a hypothesis that pestalotioprolide D could be an artifact of 7-O-methylnigrosporolide. Cytotoxic activity of both synthetic compounds against six human cancer cell lines was evaluated. Synthetic pestalotioprolide D showed more potent cytotoxic activity against all cancer cell lines tested than 7-O-methylnigrosporolide, and the SiHa cervical cancer cell line was the most sensitive cell to both synthetic compounds.

Two new ɑ-pyrone derivatives from the endophytic Diaporthe sp. ECN371

Diaportholides A (1) and B (2), two polyketides with ɑ-pyrone moieties, were isolated from the cultures of an endophytic Diaporthe sp. ECN371 isolated from Orixa japonica, together with four known polyketides, phomopsolide B (3), phomopsolidones A (4) and B (5), and 5-[(1R)-1-hydroxyethyl]-γ-oxo-2-furanbutanoic acid (6). The structures of 1 and 2 were determined by extensive analysis of NMR and MS spectroscopic data. Furthermore, the structure of 2 was confirmed by analyzing the single-crystal X-ray diffraction data. The luciferase reporter gene assay revealed that among all isolated compounds (1-6), 3, a known ɑ-pyrone derivative, exhibited agonistic activity against the peroxisome proliferator-activated receptor ɑ, which is an important regulator of lipid metabolism in humans.

Metal-Free Stereoselective Addition of Propiolic acids to Ynamides: A Concise Synthetic Route to Highly Substituted Ene-Diyne/Dienyne-(E)-N,O-Acetals

A straight forward and sustainable approach for 1,2-addition of propiolic acids to ynamide has led to bench stable sp2 (E)-enol-enamides of enediynes & dienynes. The reaction is chemo, regio, as...

Vibrational optical activity for structural characterization of natural products

This review presents the recent progress towards elucidating the structures of chiral natural products and applications using vibrational optical activity (VOA) spectroscopy.

Unbiased Determination of Absolute Configurations by vis-à-vis Comparison of Experimental and Simulated Spectra: The Challenging Case of Diplopyrone

A new experimental-computational strategy for the determination of the absolute configuration (AC) of complex chiral molecules is proposed by combining diverse experimental spectroscopies with quantum-mechanical simulations well beyond the current computational practice. Key features are the conformer search and relative stability evaluation performed by a new stochastic two-level tool followed by a vis-à-vis comparison of experimental and computed spectra without any ad hoc adjustment. The entire computational procedure is embedded in the user-friendly VMS software, and its reliability is granted by the inclusion of mechanic/electric/magnetic anharmonicity as well as ro-vibrational and vibronic couplings by means of generalized perturbation theory in conjunction with double-hybrid functionals combined with empirical dispersion contributions and suitable basis sets. To test and validate the new approach, the puzzling case of diplopyrone, a fungal phytotoxic metabolite, has been chosen: the close match between new experimental and simulated infrared absorption and vibrational circular dichroism spectra has led to the unbiased evaluation of its AC.

Synthesis and antimicrobial activities of N6-hydroxyagelasine analogs and revision of the structure of ageloximes

(+)-N⁶-Hydroxyagelasine D, the enantiomer of the proposed structure of (-)-ageloxime D, as well as N⁶-hydroxyagelasine analogs were synthesized by selective N-7 alkylation of N⁶-[tert-butyl(dimethyl)silyloxy]-9-methyl-9H-purin-6-amine in order to install the terpenoid side chain, followed by fluoride mediated removal of the TBDMS-protecting group. N⁶-Hydroxyagelasine D and the analog carrying a geranylgeranyl side chain displayed profound antimicrobial activities against several pathogenic bacteria and protozoa and inhibited bacterial biofilm formation. However these compounds were also toxic towards mammalian fibroblast cells (MRC-5). The spectral data of N⁶-hydroxyagelasine D did not match those reported for ageloxime D before. Hence, a revised structure of ageloxime D was proposed. Basic hydrolysis of agelasine D gave (+)-N-[4-amino-6-(methylamino)pyrimidin-5-yl]-N-copalylformamide, a compound with spectral data in full agreement with those reported for (-)-ageloxime D.

A synthetic study toward the core structure of (-)-apicularen A

A concise synthetic strategy towards the core structure of (-)-apicularen A has been described in an 11-step synthetic sequence from a known intermediate. The key steps include tandem isomerization followed by C-O and C-C bond-forming reactions and iodocyclization strategies for the synthesis of a bicyclic ether embedded in the macrolactone ring. The applied reagent-controlled Keck-Maruoka allylation, Lin Pu alkynylation and Ricket-Diels-Alder reactions were used to simplify the synthetic sequence of related natural products. An intramolecular Yamaguchi lactonization constructed the macrolactone core, while the attempt to install the C11 hydroxyl chiral centre either under catalytic hydrogenation conditions or oxidative conditions was not successful.

Three-component reaction to synthesize E-vinyl silyl anti-1,2-diols via sequential [1,4]-O-to-O/[1,4]-C-to-O silyl migrations

A three-component reaction of geminal bis(silyl) allyl silyl ether, aldehyde and electrophile has been developed to synthesize trisubstituted E-vinyl silyl anti-1,2-diols. The approach features a sequential [1,4]-O-to-O/[1,4]-C-to-O silyl migrations process.