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• Kaurenoic or beyerenoic acid as substrates to explore stereoselective Prins reaction. • Quirality from natural diterpenes directly influences the Prins-cyclization process. • Highly stereoselective Prins-cyclization in diterpene skeletons favors fused oxane ring. • The mechanism of Prins-cyclization is proposed and supported by computational means. • Cytotoxic potential of kauroxane and beyeroxane is explored in vitro assays. A semisynthetic strategy to access novel kauroxane or beyeroxane compounds from ent ‑kauranal or ent ‑beyerenal, respectively, is described. A Prins cyclization was used as a key step reaction to synthesize diterpene-tetrahydropyran hybrid compounds with high stereoselectivity by using 3-buten-1-ol as oxane precursor and indium trichloride as the Lewis acid catalyst. The absolute configurations of new compounds were determined by mechanistic means and supported with DFT calculations, as well as considering the stereoselectivity behavior associated with the chiral purity of diterpenes and their conformational restrictions. The structures were elucidated by their physical and spectroscopic data. Finally, the antiproliferative activity of the target molecules was done, being moderately bioactive. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract The surface extract of an accession of Psiadia punctulata (DC.) Vatke (Asteraceae) growing in Saudi Arabia was investigated for its phytochemical composition. A bio-guided investigation of the extract led to the isolation of thirteen ent -kaurane and trachylobane diterpenes and seventeen compounds previously described, including nine flavonoids and eight diterpenes. Three flavonoids and one ent -kaurane diterpene showed antimicrobial activity with MIC100 values ranging from 25 to 150 μg/ml. The extract showed antibacterial activity against Staphylococcus aureus (MIC 100 = 180 μg/ml) and antifungal activity against Candida albicans (MIC 0 = 130 μg/ml). The isolated 3′,4′,5,7-tetramethoxyflavone, at a concentration of 40 μg/ml, displayed the ability to reduce biofilm formation of S. aureus and C. albicans by 50% and 90% respectively. Graphical abstract Image 1 Highlights • The surface extract of Psiadia punctulata from Saudi Arabia was investigated. • Thirteen previously undescribed ent -kaurane and trachylobane diterpenes were isolated. • Nine known flavonoids and eight known diterpenes were also isolated. • The antimicrobial activity of the extracts, fractions and isolates was evaluated. [ABSTRACT FROM AUTHOR]

Abstract: The main diterpenoids in the roots of Arctopus (Apiaceae, tribe Saniculeae) have been identified for the first time. The major compounds are manool, ent-trachyloban-19-oic acid and a kauren-19-oic acid, while methyl-16β-hydroxy-ent-kaur-11-en-19-oate is a minor diterpene. Comparative studies of non-polar extracts by means of LC–MS showed that the isolated main compounds are present in all three species of Arctopus. The study also revealed that the diterpenoid pattern in Arctopus is very similar to that of the genus Alepidea. The tuberous roots of Arctopus and the rhizomes and roots of Alepidea are important traditional medicines in South Africa, used mainly for infections and respiratory ailments. Their efficacy is ascribed to antimicrobial and anti-inflammatory activity. The known biological activities of the isolated diterpenes provide a scientific rationale for the traditional uses. The chemical similarity in diterpenoids also supports the idea that the two genera are closely related, despite their conspicuous morphological differences. [Copyright &y& Elsevier]

Abstract: A new ent-kaurane diterpenoid, together with eight known ent-kauranes, were isolated from the petroleum ether and acetone extracts of the whole plant of Sideritis congesta P.H. Davis & Hub.-Mor. and their structures were elucidated as the new compound ent-7α-acetoxy-16β,18-dihydroxy-kaurane (7-acetyldistanol) (1) and the known compounds ent-3β,7α-dihydroxy,18-acetoxy-15β,16β-epoxykaurane (epoxyisolinearol) (2), sideroxol (3), sideridiol (4), siderol (5), 7-epicandicandiol (6), foliol (7), linearol (8) and sidol (9). Characterization of compounds 1–9 was based on spectral analyses and comparison with reported data, particularly the new compound 1 was identified by 1D- and 2D-NMR and mass spectroscopic analyses. The antioxidant potential of the extracts, and also of the ent-kauranes except for 7, was investigated by three methods including β-carotene bleaching method, free radical scavenging activity and superoxide anion scavenging activity. The anticholinesterase activity was also evaluated for the ent-kauranes except for 7, and most of the diterpenes exhibited weak acetylcholinesterase inhibitory activity. However, almost all diterpenes exhibited some inhibitory activity against butyrylcholinesterase; particularly, compounds 3 and 6 exhibited better BChE inhibitory activity than the standard compound galanthamine. [Copyright &y& Elsevier]

Abstract: The paper presents the influence of mechanochemical activation of the Slovak brown coal to make the organic structure of coal accessible for the extraction agent. It was proved that mechanical activation of optimally ground coal sample (20min) produced ultra-fine and nano-particles with specific surface of 3.79m2/g. The distribution density curves show two maxima at 6.5μm and 42nm, respectively. The identification of 16β(H)-kaurane in the coal extract was performed after the low-temperature supercritical fluid extraction of the coal powders with and without modifier. GC–MS chromatograms present the favourable effect of the modifier. It is well known, that the kaurane derivatives display biological activity. [Copyright &y& Elsevier]