Calofolic acids A-F, chromanones from the bark of Calophyllum scriblitifolium with vasorelaxation activity

Calofolic Acid-A from Calophyllum scriblitifolium Bark Has Vasorelaxant Activity via Indirect PKA Activation Caused by PI-3 Kinase Inhibition in Rat Vascular Smooth Muscle Cells

Previously, we isolated 2R,3S,15R-calofolic acids (CAs) from Calophyllum scriblitifolium bark, which showed vasorelaxant activity on phenylephrine (PE)-precontracted rat aortic rings. Although the effect was suggested to be induced via an extracellular Ca²⁺-independent manner and mainly acts on vascular smooth muscle, the exact mechanism of action of CAs remained unclear. Thus, this study investigated the detailed mechanism of calofolic acid-A (CA-A) induced vasorelaxation in an aortic ring specimen using rat vascular smooth muscle cells (VSMCs). The levels of PE-induced phosphorylation on MLC Ser19 decreased in VSMCs pretreated with CA-A. CA-A also decreased the phosphorylation of MYPT1 Thr696 and MYPT1 Thr853. On the other hand, CA-A increased the PE-induced phosphorylation of MYPT1 Ser695 and MYPT1 Ser668, which are reported to be phosphorylated by a cAMP-dependent protein kinase (PKA). CA-A slightly increased PKA substrate phosphorylation in a concentration-dependent manner. Furthermore, CA-A enhanced isoproterenol (ISO)-induced cAMP accumulation and PKA substrate phosphorylation. Treatment with PI-3 kinase (PI3K) inhibitor, LY294002, enhanced ISO-induced cAMP accumulation and PKA substrate phosphorylation in the same manner as CA-A treatment. Furthermore, CA-A was found to directly inhibit PI3K enzyme activity in a dose-dependent manner. Taken together, the present study indicated that CA-A induces vasorelaxation through an indirectly activated PKA-MYPT1 pathway caused by inhibition of PI3K activity.

Caloforines A-G, coumarins from the bark of Calophyllum scriblitifolium

Bioactivity-guided separation of the methanol extract of Calophyllum scriblitifolium bark led to the isolation of five new pyranocoumarins, caloforines A–E (1–5) and two new coumarins, caloforines F and G (6 and 7). Their structures were elucidated by 1D and 2D NMR spectroscopy, and their absolute configurations were investigated by a combination of CD spectroscopy and DFT calculation. Caloforines A–F (1–6) showed moderate antimalarial activity against Plasmodium falciparum 3D7 strain.

NMR and X-ray studies of apetalic acid isolated from Calophyllum brasiliense and of its chiral amides

The tropical tree Calophyllum brasiliense Cambess. (Clusiaceae) grows in rain forests from Brazil to Mexico. Its leaves, as well as those of other Calophyllum species, are rich sources of chromanone acids, such as apetalic acid, isoapetalic acid, and their derivatives. Apetalic acid has shown significant antimycobacterial activity. The biological activity of apetalic acid has been related to the configuration of three asymmetric centers and the stereochemistry of the molecule; however, the C-19 configuration in the acidic side chain has not been fully resolved. For this reason, the unequivocal determination of the absolute configuration by means of X-ray crystallography in a sample of unique homogeneous apetalic acid stereoisomer was the most important point to start this study. Chiral amides were prepared using the carboxyl group. We determined the C-19 stereochemistry of apetalic acid and its specific chiral derivatives using NMR, X-ray diffraction, and molecular mechanics. Finally, we observed that steric hindrance in the side chain of apetalic acid leads to restriction of rotation around the pivotal linkage C-10–C-19, establishing chiral centers at C2(R), C3(S), and C19(R). We were able to separate the derivatives of these two high-rotatory-barrier conformers of apetalic acid by forming diastereoisomeric amides with phenylglycine methyl ester having a chiral center at C-2′. Our results confirmed the existence of atropisomerism in the apetalic acid molecule.

Using 13 C-NMR dereplication to aid in the identification of xanthones present in the stem bark extract of Calophyllum brasiliense

INTRODUCTION

Xanthones are metabolites with a variety of biological properties. The Clusiaceae family, which until recently included the genus Calophyllum, is recognised for its production of monohydroxylated and polyhydroxylated xanthones. Presently, C. brasiliense is the only Calophyllum spp. known to occur in the Yucatan peninsula.

OBJECTIVE

To use a combination of traditional phytochemical methods and carbon-13 nuclear magnetic resonance (¹³ C-NMR) dereplication analysis to identify xanthones in the stem bark of C. brasiliense.

MATERIAL AND METHODS

Initial fractionation and purification of the stem bark extract of C. brasiliense produced macluraxanthone (1). Additional xanthones, together with chromanones and terpenoids, were identified using ¹³ C-NMR dereplication analysis in different semipurified fractions obtained from the low and medium polarity fractions of the stem bark extract of C. brasiliense.

RESULTS

Initial identification of macluraxanthone (1) was confirmed by ¹³ C-NMR dereplication analysis; additionally, ¹³ C-NMR dereplication analysis allowed the identification of a number of monohydroxylated and polyhydroxylated xanthones, together with chromanones and terpenoids.

CONCLUSION

This study confirms C. brasiliense as a rich source of xanthones and the ¹³ C-NMR dereplication analysis as a suitable method to quickly identify the presence of different families of secondary metabolites in semipurified fractions.

Walsogynes H-O from Walsura chrysogyne

Eight new limonoids, walsogynes H–O (1–8) were isolated from the barks of Walsura chrysogyne, and their structures were determined on the basis of the 1D and 2D NMR data. Walsogynes H–M (1–6) and O (8) were concluded to be 11,12-seco limonoids with a dodecahydro-1H-naphtho[1,8-bc:3,4-c′]difuran skeleton, and walsogyne N (7) to be 11,12-seco limonoid sharing a unique dodecahydronaphtho[1,8-bc:5,4-b′c′]difuran skeleton. Walsogynes H–O (1–8) exhibited potent antimalarial activity against Plasmodium falciparum 3D7 strain with IC₅₀ value of 2.5, 2.6, 1.6, 2.5, 1.5, 2.6, 2.1, and 1.1 µM, respectively.

Synthesis of methanesulfone-containing tetrasubstituted carbon stereocenters

A methanesulfonylation reaction for the synthesis of sulfone-containing tetrasubstituted carbon stereocenters is described for the first time by simple treatment of indanedione-chromanone synthons with Et3N and easily accessible MsCl without any use of organometallic chemistry. This technology gave the corresponding valuable chromone-based 2-methanesulfonylated 1,3-indanediones in good yields (up to 89% yield) under mild conditions. The present work provides an attractive strategy for the construction of biologically interesting sulfone-containing tetrasubstituted carbon stereocenters, which might be valuable in medicinal chemistry.

Thermal-mediated [1,3]-hydrogen transfer as the key step: access to oxindole-chromone hybrid collection with structural diversity

Inspired by the chemistry and biology of chromone and oxindole derivatives, herein we report the first example of thermal-mediated [1,3]-hydrogen transfer as the key step for the efficient synthesis of oxindole-chromone hybrid collections 2, which avoids additional catalyst and solvent conditions. All the oxindole-chromones 2 are smoothly obtained in >99% yields in all cases, avoiding column chromatography purification. In particular, the products 2 can act as potential synthons for further elaboration in structural diversity, which might be valuable in organic and medicinal chemistry.

Computationally-assisted discovery and structure elucidation of natural products

Computer hardware development coupled with the development of quantum chemistry, new computational models and algorithms, and user-friendly interfaces have lowered the barriers to the use of computation in the discovery and structure elucidation of natural products. Consequently, the use of computational chemistry software as a tool to discover and determine the structure of natural products has become more common in recent years. In this review, we provide several examples of recent studies that used computer technology to facilitate the discovery and structure determination of various natural products.

Cycloartane Triterpenoids with Anti-melanin Deposition Activity

Bioactivity guided separation of the extract of Malaysian Garcinia sp. resulted in the isolation of 23-acetoxy-mangiferonic acid (1) and the absolute configuration of C-23 was elucidated to be R by the advanced Mosher's method. The anti-melanin deposition activity of 1 was caused by the down regulation of tyrosinase gene expression.

Chemical Constituents from the Root Bark of Calophyllum inophyllum

A new chromanone derivative, namely caloinophyllin B (1), along with seventeen known compounds 2–18 were isolated from the root bark of Calophyllum inophyllum. The structures of all isolated compounds (1–18) were determined by spectroscopic methods as well as comparison with previous reports in the literature. To the best of our knowledge, compounds 1, 3, 6, 8, 11–14 and 16 were isolated from this plant for the first time. Moreover, all isolated compounds (1–18) were evaluated for their cytotoxicity against KB and Hela S-3 cell lines. Compound 8 exhibited moderate activity toward KB and Hela S-3cells with the IC50 values of 25.8 and 18.1μM, respectively.

Caloinophyllin A, a new chromanone derivative from Calophyllum inophyllum roots

A new chromanone derivative, namely caloinophyllin A (1), along with eight known compounds (2-9), nobiletin (2), pentamethylquercetin (3), 3,5,7,4'-tetramethoxyflavone (4), 5,7,4'-trimethoxyflavone (5), 1,5-dihydroxyxanthone (6), 1,8-dimethoxy-2-hydroxyxanthone (7), 1,6-dihydroxy-7-methoxyxanthone (8) and 4-methoxycaffeic acid (9) were isolated from the roots of Calophyllum inophyllum. The structures of all the isolated compounds (1-9) were fully characterised using spectroscopic data, as well as comparison with the previous literature data. In addition, the quantum chemical calculation has been used to confirm the conformation of 1. Moreover, all isolated compounds were assessed for their in vitro cytotoxicity against five human cancer cell lines.