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Three new Mitrephora species (Annonaceae), M. langsuanensis sp. nov. , M. sirindhorniae sp. nov. and M. sukhothaiensis sp. nov. , are described from Thailand. Mitrephora langsuanensis resembles M. macclurei , but its leaves have more secondary veins, and its flowers have more carpels, with yellow-and-pink striped outer petals with a margin that becomes undulate with age. Mitrephora sirindhorniae resembles M. tomentosa , but has larger sepals and petals, longer flowering pedicels, and shorter monocarp stipes, with monocarps that have a longitudinal ridge. Mitrephora sukhothaiensis is distinct from its Thai congeners in having outer petals that reflex at maturity and inner petals with a pair of appendages on the margin adaxially. The addition of these three new taxa raises the total number of Mitrephora species in Thailand to 14. An identification key for Thai species is provided.

Mitrephora sirikitiae Weeras., Chalermglin & R.M.K. Saunders has been reported as a rich source of lignans that contribute to biological activities and health benefits. However, cellular anti-inflammatory effects of M. sirikitiae leaves and their lignan compounds have not been fully elucidated. Therefore, this study aimed to investigate the anti-inflammatory activities of methanol extract of M. sirikitiae leaves and their lignan constituents on lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 mouse macrophage cells. Treatment of RAW 264.7 cells with the methanol extract of M. sirikitiae leaves and its isolated lignans, including (−)-phylligenin (2) and 3′,4-O-dimethylcedrusin (6) significantly decreased LPS-induced prostaglandin E2 (PGE2) and nitric oxide (NO) productions. These inhibitory effects of the extract and isolated lignans on LPS-induced upregulation of PGE2 and NO productions were derived from the suppression of cyclooxygenase 2 (COX-2) and inducible nitric oxide synthase (iNOS) production, respectively. In addition, treatment with 2-(3,4-dimethoxyphenyl)-6-(3,5-dimethoxyphenyl)-3,7-dioxabicyclo[3.3.0]octane (3) and mitrephoran (5) was able to suppress LPS-induced tumor necrosis factor alpha (TNF-α) secretion and synthesis in RAW 264.7 cells. These results demonstrated that M. sirikitiae leaves and some isolated lignans exhibited potent anti-inflammatory activity through the inhibition of secretion and synthesis of PGE2, NO, and TNF-α.

Annonaceae, comprising approximately 107 genera and 2400 species, is the largest family among early-divergent Magnoliales. Previous studies have concentrated on the binding mechanism that holds together the four members of tetrads in Annonaceae. However, the development mechanisms of different tetrad types remain largely unknown. Mitrephora tomentosa was found to exhibit five permanent tetrad types, with two or three of them existing in the same microsporangium, which is ideal for studying the formation mechanisms of different permanent tetrad pollens in a single microsporangium and explaining the relationship between cytokinesis and pollen tetrad types. The ontogenetic development of the different tetrads in M. tomentosa was investigated using electron microscopy technologies, histochemical staining, and immunocytochemistry. During meiosis, pollen mother cells produce decussate and tetragonal tetrads by successive cytokinesis and produce tetrahedral and rhomboidal tetrads by simultaneous cytokinesis. Bidirectional callose deposition was observed in tetrahedral, tetragonal, rhomboidal, and decussate tetrads. The variations in the process of microsporogenesis randomly accumulate and manifest as different combinations of cytokinesis and callose deposition, leading to the formation of differently shaped tetrads. In mature permanent tetrad pollens, four microspores are connected by both simple cohesion and cytoplasmic channels, which also play an important role in maintaining the synchronization of the tetrad members.

Mitrephora wangii, an ethnomedicinal plant, has been used as a natural antibiotic and immunity booster in Thailand. A total of 22 fungi were isolated from M. wangii flowers. The fungal isolates were categorized into six genera including Agrocybe, Aspergillus, Colletotrichum, Nigrospora, Puccinia and Ustilago. Most extracts exhibited antibacterial activity against at least one of the test bacteria. Aspergillus sp. MFLUCC16-0845 was identified as the most bioactive fungus. Chemical composition of Aspergillus sp. MFLUCC16-0845 investigated using gas chromatography–mass spectrometry indicated that the major antibacterial compound was β-thujaplicin. Moreover, the newly isolated Aspergillus sp. MFLUCC16-0845 could be exploited as a potential source of bioactive compounds and plant defense activators. In addition, it is the first time that strain of Aspergillus sp. isolated and cultured from M. wangii flowers could produce β-thujaplicin at high yield with strong antimicrobial spectrum, which may lead to wide utilization in producing cosmetics and clinical products.

A new species, Mitrephoramonocarpa R.M.K.Saunders & Chalermglin, sp. nov. (Annonaceae), is described from Surat Thani Province in Peninsular Thailand. It resembles two other species, M.alba Ridl. and M.keithii Ridl., with which it is broadly sympatric, but can be distinguished by its solitary flowers (not borne in thyrsoid inflorescences as in most other Mitrephora species), single carpel per flower (and hence single monocarp per fruit) and the lack of a monocarp stipe. A key to the nine Mitrephora species in Thailand is provided.

A comprehensive taxonomic revision of the genus Mitrephora (Annonaceae) in Cambodia (Kampuchea), Laos, and Vietnam is presented. Eight species are recognized, including five that are newly described, viz. M. calcarea sp. nov., M. macclurei sp. nov., M. pallens, M. petelotii sp. nov., M. phanrangensis sp. nov., M. poilanei sp. nov., M. teysmannii, and M. tomentosa (inclusive of M. thorelii). Previous taxonomic confusion regarding the delimitation of M. calcarea is clarified and the name is validated for the first time. The correct application of the name M. maingayi is clarified: although the name has been used to refer to a species that is distinct within the region, the name itself is a synonym of M. teysmannii. Most of the Indochinese collections determined as “M. maingayi” are shown here to represent a new species, M. macclurei.

Phylligenine, together with quebrachitol, stigmasterol and two aporphine alkaloids—oxoputerine and liriodenine—were isolated from the twigs of Mitrephora vulpina C.E.C. Fisch. They were evaluated for their ability to inhibit platelet activating factor (PAF) receptor binding to rabbit platelets using 3H-PAF as a ligand and their antiplatelet aggregation effect in human whole blood induced by arachidonic acid (AA), collagen and adenosine diphosphate (ADP). Of all the compounds tested, phylligenin and quebrachitol exhibited potent and concentration-dependent inhibitory effects on PAF receptor binding, with IC50 values of 13.1 and 42.2 µM, respectively. The IC50 value of phylligenin was comparable to that of cedrol (10.2 µM), a potent PAF antagonist. Phylligenin also showed strong dose-dependent inhibitory activity on platelet aggregation induced by AA and ADP.

Chromatographic separation of leaves and twigs from M. wangii had led to the isolation of conocarpan ( 1 ) and 3′-methoxyconocarpan ( 2 ). These structures were assigned on the basis of spectroscopic methods. Compound 1 was modified by organic reactions and the modified compound 5 exhibited potent antifungal, Pyricularia oryzae . The method used poisoned food technique with mycelial growth inhibition for 14 days, 57 % (100 ppm). Compound 5 was stronger than mancozeb which the fungi toxicity drug used as a positive control.

The leaf oils of seven species from the family Annonaceae, growing in Queensland, Australia, have been examined. Artabotrys sp. (Claudie River B.Gray 3240) produced oil in poor yield in which unidentified oxygenated sesquiterpenes accounted for approximately 80% of the oil. Uvaria rufa gave an oil rich in sesquiterpenes, in which the principal component was alpha-humulene (50%), while in Uvaria concava the principal component was spathulenol (32%). Benzyl benzoate was also present (5%) in U. rufa. In Cyathostemma micranthum the principal components were caryophyllene oxide (26%), spathulenol (11%) and benzyl benzoate (4%). The oil of Mitrephora zippeliana existed in two forms in which either monoterpenes were more prominent with alpha-pinene (13%) and beta-pinene (15%) being the major components together with the sesquiterpenes caryophyllene oxide (10%), spathulenol (10%) and beta-caryophyllene (8%), or sesquiterpenes were prominent with beta-caryophyllene (18%), alpha-humulene (7%), gamma-curcumene (4%), bicyclogermacrene (4%), ar-curcumene (5%), caryophyllene oxide (3%) and spathulenol (5%) being the principal components. Goniothalamus australis presented a leaf oil that contained significant amounts of both mono- and sesquiterpenes; one sample contained pinocarvone (10%) and trans-pinocarveol (17%) as the principal monoterpenes, while a second collection contained alpha-pinene (10-11%) as the principal component. Cananga odorata gave a leaf oil in which the major components were beta-caryophyllene (34-52%), sabinene (1-20%), alpha-humulene (6-11%) and alpha-pinene (1-17%).