A new iridoid glucoside with an ether linkage between C-3 and C-10 and a novel nonglycosidic iridoid with an ether linkage between C-3 and C-6 and a lactonic linkage at C-1, named macrophylloside (1) and macrophyllide (2), respectively, were isolated from the leaves of Rothmannia macrophylla, along with six known iridoids. Their structures were established by NMR and MS spectroscopies.
A new megastigmane diglycoside was isolated from the leaves of Carallia brachiata. The structure was determined by spectroscopic methods as 3-hydroxy-5,6-epoxy-beta-ionol -3-O-beta-apiofuranosyl-(1-->6)-beta-glucopyranoside (1). Additionally, 29 known compounds consisting of two megastigmanes, one 1,2-dithiolane derivative, seven aromatic compounds, five condensed tannins, 12 flavonoids, and two glyceroglycolipids were isolated and identified.
Methanolic extracts of the leaves, stems, and roots of Phyllagathis rotundifolia collected in Malaysia yielded seven galloylated cyanogenic glucosides based on prunasin, with six of these being new compounds, prunasin 2',6'-di-O-gallate (3), prunasin 3',6'-di-O-gallate (4), prunasin 4',6'-di-O-gallate (5), prunasin 2',3',6'-tri-O-gallate (6), prunasin 3',4',6'-tri-O-gallate (7), and prunasin 2',3',4',6'-tetra-O-gallate (8). Also obtained was a new alkyl glycoside, oct-1-en-3-yl alpha-arabinofuranosyl-(1-->6)-beta-glucopyranoside (9). For compounds 3-8, the galloyl groups were individually linked to the sugar moieties via ester bonds. All new structures were established on the basis of NMR and MS spectroscopic studies. In addition, prunasin (1), gallic acid and its methyl ester, beta-glucogallin, 3,6-di-O-galloyl-D-glucose, 1,2,3,6-tetra-O-galloyl-beta-D-glucose, strictinin, 6-O-galloyl-2,3-O-(S)-hexahydroxydiphenoyl-D-glucose, praecoxin B, and pterocarinin C were isolated and identified. The isolation of 1 and its galloyl derivatives (3-8) from a Melastomataceous plant are described for the first time.
Enzyme inhibitory activities of 14 iridoids previously obtained from two Malaysian medicinal plants, Saprosma scortechinii and Rothmannia macrophylla, were evaluated in vitro using soybean lipoxygenase and bovine testis hyaluronidase. Most of the iridoids, including asperulosidic acid, paederosidic acid, and an epimeric mixture of gardenogenins A and B, did not show any effect on the enzyme activities, except for the bis-iridoids, which inhibited the lipoxygenase activity with their IC(50) values of approximately 1.3 times that of a known inhibitor, fisetin. Structural modification of asperulosidic acid and paederosidic acid through enzymatic hydrolysis by beta-glucosidase resulted in their inhibition towards the enzyme activities, and these activities were enhanced by the presence of some amino acids (lysine, leucine or glutamic acid) or ammonium acetate. Mixtures of gardenogenins A and B; isomers of non-glucosidic iridoids, incubated with amino acid or ammonium acetate did not show any inhibitory effect on the enzyme activities during the 6 h incubation period, except for lysine where spontaneous reaction between the iridoids and amino acid resulted in the inhibition of lipoxygenase activity. The results from these biomimetic reactions suggested that the iridoid aglycons and the intermediates formed by these reactive species could inhibit the enzyme activities, and thus substantiate previous reports that the formation of iridoidal aglycons is a prerequisite for the iridoid glycosides to demonstrate some of the biological activities. In addition, the results also indicated that it is worthwhile to further explore these intermediates as potential anti-inflammatory agents.
Six new sulfur-containing bis-iridoid glucosides, saprosmosides A-F (1-6), were isolated from the leaves of Saprosma scortechinii. From the stems of this same plant, two new iridoid glucosides, 3,4-dihydro-3-methoxypaederoside (8) and 10-O-benzoyldeacetylasperulosidic acid (12), were isolated. Their structures were elucidated by means of chemical, NMR, and mass spectroscopic methods. Additionally, 11 known iridoid glucosides were isolated and characterized as deacetylasperuloside, asperuloside, paederoside (7), deacetylasperulosidic acid (9), scandoside, asperulosidic acid, 10-acetylscandoside, paederosidic acid (10), 6-epi-paederosidic acid (11), methylpaederosidate, and monotropein. The structures of the new bis-iridoid glucosides were formed by intermolecular esterification between the glucose and carboxyl groups of three monomeric iridoid glucosides (7, 9, and 10).
A further investigation of the leaves and stems of Saprosma scortechinii afforded 13 compounds, of which 10 are new compounds. These were elucidated as the bis-iridoid glucosides, saprosmosides G (1) and H (2), the iridoid glucoside, 6-O-epi-acetylscandoside (3), and the anthraquinones, 1-methoxy-3-hydroxy-2-carbomethoxy-9,10-anthraquinone (4), 1-methoxy-3-hydroxy-2-carbomethoxy-9,10-anthraquinone 3-O-beta-primeveroside (5), 1,3-dihydroxy-2-carbomethoxy-9,10-anthraquinone 3-O-beta-primeveroside (6), 1,3,6-trihydroxy-2-methoxymethyl-9,10-anthraquinone (7), 1-methoxy-3,6-dihydroxy-2-hydroxymethyl-9,10-anthraquinone (8), 1,3,6-trihydroxy-2-hydroxymethyl-9,10-anthraquinone 3-O-beta-primeveroside (9), and 3,6-dihydroxy-2-hydroxymethyl-9,10-anthraquinone (10). Structure assignments for all compounds were established by means of mass and NMR spectroscopies, chemical methods, and comparison with published data. The new anthraquinones were derivatives of munjistin and lucidin.