A Themed Issue in Honor of Professor K. Hüsnü Can Baser—Outstanding Contributions in the Fields of Pharmacognosy, Phytochemistry, Botany and Ethnopharmacology

Dear Colleagues, [...].

in November-December 2012 in Egypt; at an FAO project on medicinal and aromatic non-wood forest products in February 2013 in Uzbekistan; and at a UNIDO project on fragrances in August 2018 in Oman. He worked as a national point of contact for the Asian-Pacific Information Network of Medicinal and Aromatic Plants (APINMAP) (1992)(1993)(1994)(1995)(1996)(1997) and Useful Plants of the Mediterranean Network (MEDUSA) in Turkey (1996)(1997)(1998)(1999)(2000). He served as Member of the Turkish Pharmacopoeia Commission , Member of the Registration Commission for Plant Drugs at the Ministry of Health (1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992) This Special Issue in honor of Prof. Baser consists of twelve articles in the form of eight research articles and four reviews. Our goal, as Guest Editors, was to make a gesture acknowledging the tremendous impact of Prof. Baser's work on the fields of pharmacognosy, phytochemistry, botany, and ethnopharmacology. We are very pleased to see the completion of this Special Issue that contains contributions from many of his colleagues and collaborators.
Most of the research articles included in this issue are focused mainly on the isolation of compounds occurring in plants. One paper, prepared by Iklas A. Khan group [1], described the isolation of one new and seven known sesquiterpenoids from copaiba oil. The new compound was elucidated as (E)-2,6,10-trimethyldodec-8-en-2-ol by use of 1D and 2D NMR and GC/Q-ToF mass spectral data analyses. The authors concluded that the isolated constituents could be used as chemical markers to evaluate the safety or quality of copaiba oil, which has been used in folk medicine for centuries as a wound-healing agent. The studies on two Aloe species, A. vera and A. plicatilis, by Rauwald et al. Another paper, [2], led to the isolation of series of phenolic polyketides such as naphthalenes (hexaketides), chromones (heptaketides), anthrones/anthraquinones (octaketides), and nonaketides. For this, Sephadex-LH20 gel filtration, combined silica gel 60-and RP18column chromatography, as well as high-speed counter-current chromatography (HSCCC) were used. The structures of all polyketides were elucidated by ESI-MS and 2D 1H/13C NMR (HMQC, HMBC) and CD spectroscopy. The isolated metabolites were further screened in vitro to identify Aloe polyketides with anti-inflammatory potential.
Bioguided isolation of volatile components with repellent activity from the essential oils obtained from Pinus and Juniperus species was carried out by Leandros A. Skaltsounis group [3]. To perform this work, they use centrifugal partition chromatography (CPC), a liquid-liquid separation method, as an isolation technique, gas chromatography-mass spectrometry (GC/MS) as an analytical tool to monitor the isolation process and, finally, all isolated compounds, fractions, as well as essential oils were evaluated for their repellent properties against Aedes albopictus. The essential oils from needles of Pinus pinea and fruits of Juniperus oxycedrus subsp. deltoides turned out to be the most active against Ae. albopictus, and of these isolated oil compounds, (−)-limonene, guaiol, germacrene D, and mixtures of (−)-limonene/β-phellandrene presented significant repellent activity (>97% repellency). This methodology could be a valuable tool in the effort to develop potent mosquito repellents which are environmentally friendly.
Centrifugal partition chromatography (CPC) in combination with normal phase flash chromatography and reversed phase preparative HPLC was used in the isolation of sesquiterpenes from myrrh resin by Jörg Heilmann and coworkers [4]. From the ethanolic extract, sixteen compounds were isolated. Two of them, 9-nor-9,10-seco-isolindestrenolide and 9,10-seco-isohydroxylindestrenolide, are novel 9,10-seco-eudesmanes and exhibited an unprecedented sesquiterpene carbon skeleton. The isolated compounds were tested in an in vitro ICAM-1 assay, and only lindestrenolide acted as moderate inhibitor of this adhesion molecule ICAM-1 with an IC 50 value of 44.8 µM.
Shaza M. Al-Massarani et al. [5] reported on the isolation of five phenolic compounds from the aerial parts of the Saudi plant Nuxia oppositifolia. These were two flavones, hispidulin and jaceosidin, and three phenylethanoid glycosides, verbascoside, isoverbascoside, and conandroside. The isolated flavones together with eleven previously isolated compounds were evaluated against the Yellow Fever mosquito, Aedes aegypti. Four compounds (β-sitosterol and oleananne-type triterpenoids) displayed adulticidal activity with LD 50 values of 2-2.3 µg/mosquito. All isolated compounds exhibited notable free radical scavenging properties, compared with the positive control.
In their research article, Györgyi Horváth and colleagues [6] focused on the isolation and identification of carotenoids from the aerial parts of Melilotus officinalis and on the effect of isolated (all-E)-lutein 5,6-epoxide on primary sensory neurons and macrophages involved in nociception as well as neurogenic and non-neurogenic inflammatory processes. The main carotenoid was isolated by column liquid chromatography (CLC), identified by spectroscopic methods, and the isolation process was monitored by HPLC technique. Then, the isolated (all-E)-lutein 5,6-epoxide was packed into RAMEB (randomly methylated-βcyclodextrin) to enhance its water solubility for in vitro functional experiments. The results showed that the tested compound suppressed mustard oil (MO)-induced TRPA1 receptor activation on primary sensory neurons, which opens perspectives for its analgesic and anti-inflammatory application.
Microbial biotransformation is an important tool in drug discovery and for metabolism studies. Erdal Bedir et al. [7] reported on the products formed during the biotransformation of a cardenolide, gitoxigenin, by the endophytic fungus Alternaria eureka 1E1BL1. Gitoxigenin was obtained, by the authors, from oleandrin isolated from the leaves of Nerium oleander, which was subjected to an acid-catalyzed hydrolysis. After 21 days of the incubation process, eight compounds were isolated, five of which were new cardenolides. Structural elucidations were accomplished through 1D/2D NMR, HR-ESI-MS and FT-IR analysis. The isolated compounds were tested for their cytotoxic activity, and 3-epi-diginatigenin exhibited the highest activity against A549, PANC-1, and MIA PaCa-2 cells without causing toxicity on healthy cell lines (MRC-5 and HEK-293).
Cholinesterase inhibition is an important treatment strategy for Alzheimer's disease, as acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are involved in the pathology of this disease. Ilkay Erdogan Orhan et al. [8] reported the cholinesterase inhibitory potential of 24 natural products from different chemical classes. Among them, only a steroidal sapogenin, smilagenin, and an alkaloid, kokusaginine, displayed inhibitory action against AChE. BChE was inhibited by only methyl rosmarinate and kokusaginine. Molecular docking experiments showed that the orientation of smilagenin and kokusaginine was mainly driven by the interactions with the peripheral anionic site (PAS) comprising residues of hAChE, while kokusaginine and methyl rosmarinate were able to more deeply access the active gorge in hBChE. These data indicate that similagenin, kokusaginine, and methyl rosmarinate are promising compounds for designing novel anti-Alzheimer's agents.
Four review papers complete this Special Issue. The first, written by Ryan D. Rattray and Ben-Erik Van Wyk [9], provides comprehensive insight into the Lamiaceae flora of southern Africa, comprising 297 species in 42 genera, 105 of which are endemic to the subcontinent. The main aim of their study was to present an up-to-date account of the botany, chemistry, and traditional uses of the family in southern Africa. In another review paper by Andrea Vasas and colleagues [10], the information concerning stilbenoids occurring in Cyperaceae species is summarized. The authors focused on the isolation, synthesis, and pharmacological properties of this group of compounds in addition to their chemotaxonomical significance. The chemistry of the cannabinoids and major noncannabinoid constituents (terpenes, non-cannabinoid phenolics, and alkaloids) occurring in Cannabis sativa, with special emphasis on their chemical structures, methods of isolation, and identification, is the subject of the next review prepared by Mohamed M. Radwan et al. [11] that was included in this Special Issue. Sansei Nishibe and coworkers [12] summarized their research studies on the biological effects of forsythia (Forsythia suspensa) leaves containing phillyrin and other polyphenolic compounds, particularly against obesity, atopic dermatitis, and influenza A virus infection, and its potential as a phytoestrogen. The authors also conclude that forsythia leaves are useful and safe as a health food containing a PDE4 inhibitor, supporting its use in the treatments of metabolic disorders and inflammatory dysregulation.
Overall, the 12 manuscripts published in the current SI cover many aspects of research conducted in the fields pharmacognosy, phytochemistry, botany, and ethnopharmacology and, we hope, provide interesting new information for scientists working in these fields.