Extraction Optimization and Structural and Thermal Characterization of the Antimicrobial Abietane 7α-Acetoxy-6β-hydroxyroyleanone

Abstract

The abietane 7α-acetoxy-6β-hydroxyroyleanone (AHR), obtained from plant extracts, is an attractive lead for drug development, given its known antimicrobial properties. Two basic requirements to establish any compound as a new drug are the development of a convenient extraction process and the characterization of its structural and thermal properties. In this work seven different methods were tested to optimize the extraction of AHR from Plectranthus grandidentatus. Supercritical fluid extraction (SFE) proved to be the method of choice, delivering an amount of AHR (57.351 μg·mg) approximately six times higher than the second best method (maceration in acetone; 9.77 μg·mg). Single crystal X-ray diffraction analysis of the ARH molecular and crystal structure carried out at 167 ± 2 K and 296 ± 2 K showed only a single phase, here dubbed form III (orthorhombic space group P222), at those temperatures. The presence of two other polymorphs above room temperature was, however, evidenced by differential scanning calorimetry (DSC). The three forms are enantiotropically related, with the form III → form II and form II → form I transitions occurring at 333.5 ± 1.6 K and 352.0 ± 1.6 K, respectively. The fact that the transitions are reversible suggests that polymorphism is not likely to be an issue in the development pharmaceutical formulations based on ARH. DSC experiments also showed that the compound decomposes on melting at 500.8 ± 0.8 K. Melting should therefore be avoided if, for example, strategies to improve solubility based on the production of glassy materials or solid dispersions are considered.

Insight the Biological Activities of Selected Abietane Diterpenes Isolated from Plectranthus spp.

“…The compound Diroy is the less bioactive abietane and this is in agreement with the more polar feature on the C-6 and C-7 positions. This polar structure-activity relationship could be explained due to a better membrane interaction [11][12][13][14][15][16][17].…”

“…Numerous studies attribute these biological properties to the diterpenes expressed by this genus [8][9][10]. Our previous studies have demonstrated that the diterpenes isolated from Plectranthus genus induce apoptosis in various cancer cell lines, including human myeloid leukaemia, and pancreatic, lung, melanoma, prostate, and breast cancer [11][12][13][14][15][16][17]. The present study focuses on the properties of abietane diterpenes (Roy, Deroy, Diroy, and Parv D) isolated from P. madagascariensis and P. ecklonii.…”

“…It is also used for colds and asthma [6]. Similarly to other members of this genus, P. madagascariensis possesses a number of secondary metabolites with antimicrobial, antioxidant or anticancer properties [15,16]. The essential oil is a rich source of 6,7-dehydroroyleanone (Deroy), i.e., an abietane diterpene with a quinone moiety [15].…”

Royleanone Derivatives From Plectranthus spp. as a Novel Class of P-Glycoprotein Inhibitors

“…Version 1.1, 2013). The extraction and isolation process of 1 and 2 were performed according to Garcia et al (2018) and Bernardes et al (2018), respectively. Isca et al (2020).…”

Anti-Migratory and Pro-Apoptotic Properties of Parvifloron D on Triple-Negative Breast Cancer Cells

“…The obtained organic extracts were filtered, and the solvent was removed by rotary evaporation [9]. The supercritical fluid extraction (SFE) was done as previously described [20].…”