Toward the Total Synthesis of Klaivanolide: Complete Reinterpretation of Its Originally Assigned Structure

Total Synthesis of γ-Alkylidenebutenolides, Potent Melanogenesis Inhibitors from Thai Medicinal Plant Melodorum fruticosum

A hitherto unreported member of γ-alkylidenebutenolides in Melodorum fruticosum (Annonaceae), (4 E)-6-benzoyloxy-7-hydroxy-2,4-heptadiene-4-olide, named as isofruticosinol (4) was isolated from the methanol extract of flowers, along with the known related butenolides, namely, the (4 Z)-isomer (3) of 4, melodrinol (1), and its (4 E)-isomer (2). To unambiguously determine the absolute configuration at the C-6 position in these butenolides, the first total syntheses of both enantiomers of 2-4 were achieved over 6-7 steps from commercially available D- or L-ribose (D- and L-5). Using the same protocol, both enantiomers of 1 were also synthesized. Based on chiral HPLC analysis of all synthetic compounds ( S- and R-1-4), all naturally occurring butenolides were assigned as partial racemic mixtures with respect to the chiral center at C-6 (enantiomeric ratio, 6 S/6 R = ∼83/17). Furthermore, the melanogenesis inhibitory activities of S- and R-1-4 were evaluated, with all shown to be potent inhibitors with IC₅₀ values in the range 0.29-2.9 μM, regardless of differences in the stereochemistry at C-6. In particular, S-4 (IC₅₀ = 0.29 μM) and R-4 (0.39 μM) showed potent inhibitory activities compared with that of reference standard arbutin (174 μM).

ROS-responsive poly(ε-caprolactone) with pendent thioether and selenide motifs

Synthesis and oxidation properties of three chalcogen-containing ROS-responsive poly(ε-caprolactone)s have been reported.

Vibrational Circular Dichroism: Recent Advances for the Assignment of the Absolute Configuration of Natural Products

Vibrational circular dichroism (VCD) emerged during the last decade as a reliable tool for the absolute configuration (AC) determination of organic compounds. The principles, instrumentation, and methodology applied prior to early 2013 were recently reviewed by us. Since VCD is a very dynamic field, the aim of this review is to update VCD advances for the AC assignment of terpenoids, aromatic compounds, alkaloids, and other natural products for the 2013–2014 period, when VCD was applied to the AC assignment of some 70 natural products. In addition, although discovered in 2012, a brief introduction to the VCD exciton coupling approach and its applications in natural products AC assignment is presented.

Vibrational Circular Dichroism: Recent Advances for the Assignment of the Absolute Configuration of Natural Products

Vibrational circular dichroism (VCD) emerged during the last decade as a reliable tool for the absolute configuration (AC) determination of organic compounds. The principles, instrumentation, and methodology applied prior to early 2013 were recently reviewed by us. Since VCD is a very dynamic field, the aim of this review is to update VCD advances for the AC assignment of terpenoids, aromatic compounds, alkaloids, and other natural products for the 2013-2014 period, when VCD was applied to the AC assignment of some 70 natural products. In addition, although discovered in 2012, a brief introduction to the VCD exciton coupling approach and its applications in natural products AC assignment is presented.

Recent advances in the use of vibrational chiroptical spectroscopic methods for stereochemical characterization of natural products

A comprehensive look into application of vibrational optical activity methods for conformational and configurational assignments in natural product molecules over the last 15 years is provided.