Silencing Tautomerization to Isolate Unstable Physalins fromPhysalis minima

Abstract

The inherent structural instability of some physalins has hampered the isolation and identification of these compounds for approximately 50 years, and an effective method to overcome these challenges remains unavailable. In the present study, the unprecedented tautomerization mechanism of unstable physalins was elucidated by performing isotopic labeling experiments and DFT calculations, which led to the successful separation of tautomers and isolation of highly pure products for the first time. As a result, 15 new physalins, physaminins A–O (1–15), as well as 17 known analogues (16–32), were isolated from the whole plants of Physalis minima L. The chemical structures of the new compounds were established by performing a comprehensive analysis of spectroscopic data, and their absolute configurations were confirmed by using computational ECD calculations and/or single-crystal X-ray diffraction analyses. All obtained isolates were evaluated for their antiproliferative effects against four human cancer cell lines (A549, HepG2, MCF-7, and SCG-7901) and two noncancerous cell lines (RAW 264.7 and human normal hepatocytes L02), as well as their anti-inflammatory activities by measuring their abilities to inhibit NO production in LPS-stimulated murine RAW 264.7 cells in vitro. Compounds 1–5, 13, 16, 18, 19, 23, and 30 exerted significant antiproliferative effects on the four human cancer lines, with IC50 values ranging from 0.2(0) to 24.7(2) μM, and these compounds were not toxic to the two noncancerous cell lines at a concentration of 10 μM. Moreover, compounds 7, 10, 11, 12, 14, 17, 22, and 27 significantly inhibited NO production, with IC50 values ranging from 2.9(1) to 9.5(2) μM.

UPLC-Q-Orbitrap-MS/MS-Guided Isolation of Bioactive Withanolides from the Fruits of Physalis angulata

“…Their structures were established by various spectroscopic data and quantum chemical calculations. Twenty-three known withanolide derivatives ( 4 – 26 ), withaminimin ( 4 ), withagulatin A ( 5 ), physagulin A ( 6 ), physagulin B ( 7 ), physagulin J ( 8 ), physapubenolide ( 9 ), physagulide J ( 10 ), (20 S , 22 R )-15α-acetoxy-5α-chloro-6β,14β-dihydroxy-1-oxowitha-2,24-dienolide ( 11 ), physagulin F ( 12 ), physalin H ( 13 ), physalin B ( 14 ), isophysalin B ( 15 ), physalin D ( 16 ), physalin G ( 17 ), physalin E ( 18 ), physalin I ( 19 ), physalin F ( 20 ), 25-OH-physalin D ( 21 ), physaminin M ( 22 ), physaminin K ( 23 ), 5α,6β-dihydroxyphysalin R ( 24 ), aromaphysalin A ( 25 ), and aromaphysalin B ( 26 ), were assigned by comparing their NMR data with those in the literature.…”

A Rapid and Sensitive LC−MS/MS Method for the Quantitation of Physalin A with Special Consideration to Chemical Stability in Rat Plasma: Application to a Pharmacokinetic Study

“…Early in 2002, researchers reported that physalin A in 50% methanol solution underwent tautomerization and generated physalin N [ 22 ]. Recently, the mechanism of physalin’s tautomerization was detailed, revealed by Zou’s group [ 23 ]. It was reported that H 2 O was the key factor leading to the instability of physalins and even a small amount of H 2 O (0.5%) in solution triggered interconversion [ 23 ].…”

“…Recently, the mechanism of physalin’s tautomerization was detailed, revealed by Zou’s group [ 23 ]. It was reported that H 2 O was the key factor leading to the instability of physalins and even a small amount of H 2 O (0.5%) in solution triggered interconversion [ 23 ]. Based on these reports, there is no doubt that physalin A is unstable in whole blood or plasma, which contains a large amount of H 2 O.…”

Cytosporones W and X: Two Mutually Converting Epimers from a Mangrove Endophytic Fungus Diaporthe sp. ZJHJYZ-1

“…Comparing lactone-type cytosporones 1&2, (±)-3 and 4, (±)-3 showed promising antimicrobial activities, which would be significantly weakened with either the aliphatic side chain oxygenated (1&2) or the 7-OH deficiency (4). As for phenyl-type cytosporones 5, 6, 7, and 8, 6 showed better antimicrobial activities, which would also be attenuated with the octanoyl oxygenated (5), shortened to be a hexanoyl (8), or the acetylethoxyl replaced by an acetylmethoxyl (7).…”

“…Tautomeric and stereoisomerized compounds are common in the field of natural products research, especially for ketone–enol, − enamine–imino, hemiketal–aldol, , and (retro-)­oxa-Micheal addition tautomerism. Convincing hypotheses were proposed to clarify the converting mechanism, and NMR calculation, acid or alkali treatment, chiral-phase high-performance liquid chromatography (HPLC) analysis, and methylation reactions were reported to verify some of those hypotheses. − …”