Total syntheses of Prelactone V and Prelactone B

Isolation and NMR Scaling Factors for the Structure Determination of Lobatolide H, a Flexible Sesquiterpene from Neurolaena lobata

A new flexible germacranolide (1, lobatolide H) was isolated from the aerial parts of Neurolaena lobata. The structure elucidation was performed by classical NMR experiments and DFT NMR calculations. Altogether, 80 theoretical level combinations with existing ¹³C NMR scaling factors were tested, and the best performing ones were applied on 1. ¹H and ¹³C NMR scaling factors were also developed for two combinations utilizing known exomethylene containing derivatives, and the results were complemented by homonuclear coupling constant (J_HH) and TDDFT-ECD calculations to elucidate the stereochemistry of 1. Lobatolide H possessed remarkable antiproliferative activity against human cervical tumor cell lines with different HPV status (SiHa and C33A), induced cell cycle disturbance and exhibited a substantial antimigratory effect in SiHa cells.

Synthetic Applications of Prins Cyclization in Natural Product Syntheses

The natural products having tetrahydropyran unit with multiple chiral centers serve as magnificent building blocks for various active pharmaceutical ingredients (APIs). 'Prins cyclization is one of the wonderful strategies to construct tetrahydropyran unit stereoselectively in asymmetric synthesis. In this account, we discuss our research efforts toward the synthesis of various natural products from the past two decades (2005-2020) by using Prins cyclization as a key step. Further, the synthetic utility of this reaction was investigated and well demonstrated on various molecules successfully.

Iron-Catalyzed Radical Cleavage/C-C Bond Formation of Acetal-Derived Alkylsilyl Peroxides

A novel radical-based approach for the iron-catalyzed selective cleavage of acetal-derived alkylsilyl peroxides, followed by the formation of a carbon-carbon bond is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the acetal moiety and the carbon electrophile. Mechanistic studies suggest that the present reaction proceeds through a free-radical process involving carbon radicals generated by the homolytic cleavage of a carbon-carbon bond within the acetal moiety. A synthetic application of this method to sugar-derived alkylsilyl peroxides is also described.

An eco-friendly N-benzoylglycine/thiourea cooperative catalyzed stereoselective synthesis of β-L-rhamnopyranosides

A new practical utility for β-stereoselective L-rhamnopyranosylations are conducted using rhamnosyl trichloroacetimidate donors in the presence of N-benzoylglycine/thiourea cooperative catalysis. This method represents the first instance where amino acid derivative N-benzoylglycine is used as a catalyst for β-L-rhamnopyranosylations. This method represents the first instance where environmentally benign amino acid derivative, such as N-benzoylglycine which is reported as less toxic and can be used as efficient catalyst for smooth transformation under eco friendly conditions. On the other hand β-stereoselectivity of rhamnosyl trichloroacetimidate donors protected with O-picoloyl groups at remote positions (C-2 and C-3) has been investigated while the glycosylation reactions of 2-O-picoloyl group substituted l-rhamnosyl donor displays predominant β-stereoselectivity. Reaction proceeded smoothly with moderate to high yield under mild reaction conditions at room temperature with 10 mol% catalyst loadings and tolerant of a wide range of glycoside acceptors.