Abstract
Phytochemical studies of Cespedesia spathulata (Ochnaceae) leaves using 1H, 13C NMR, and GC-MS have led to the isolation of some metabolites identified for the first time in these species such as cathechin, epicatechin, vitexin, orientin, 6''-O-acetyl-vitexin, sitosterol, stigmasterol, phytol, 4,5-dihydrovomifoliol and a mixture of aliphatic methyl esters, together with ochnaflavone, which was previously isolated from this plant. The modulating activity of some fractions and compounds from Cespedesia spathulata towards tyrosinase enzyme was assayed by spectroscopic and theoretical means/experiments. The dichloromethane fraction (133 μg mL-1) and ochnaflavone (333 μM) inhibited tyrosinase activity by 20 % and 2.0 %, respectively, whereas the ethyl acetate fraction (666 μg mL-1) and ±catechins (catechin and epicatechin - 800 μM) activated it by 104 % and 384 %, respectively. Quantum chemical calculations suggested that catechin and epicatechin are better activators than L-DOPA by interacting with Cu (II) ions. Molecular docking results suggested that hydrogen bonding and hydrophobic interactions are the main binding forces between each tyrosinase activator and the amino acid residues inside the active protein binding pocket.
Highlights
Cespedesia spathulata (Ruiz & Pav.) Planch., Ochnaceae (Sastre 1995), is recognized from its spatulate leaves with oboval and lax inflorescences (Chacon et al 2011)
The polymerization reactions that synthesize melanin occur in cells named melanocytes and the tyrosinase enzyme (EC 1.14.18.1) is the main protein responsible for the conversion of the tyrosine substrate to melanin by melanocytes
We report here the extraction, fractionation and identification of compounds isolated from extracts of C. spathulata leaves
Summary
Cespedesia spathulata (Ruiz & Pav.) Planch., Ochnaceae (Sastre 1995), is recognized from its spatulate leaves with oboval and lax inflorescences (Chacon et al 2011). The biosynthesis of biflavonoids is in accordance with the profile of the species belonging to the Ochnaceae family, mainly in the Luxemburgieae tribe (Bandi et al 2012, Fidelis et al 2014). In this phytochemical study we confirmed the presence of the biflavonoid ochnaflavone, previously identified in Cespedesia species (Lobstein et al 2004), in addition to three flavones and two catechins. Tyrosinase first oxidizes the tyrosine substrate to dihydroxyphenylalanine (L-DOPA), and subsequently oxidizes L-DOPA to L-DOPAquinone.
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