Petar D. Marin

Leaf flavonoid glycosides as chemosystematic characters in Ocimum

Abstract Thirty-one accessions of nine species belonging to three subgenera of Ocimum (basil, family Lamiaceae) were surveyed for flavonoid glycosides. Substantial infraspecific differences in flavonoid profiles of the leaves were found only in O. americanum , where var. pilosum accumulated the flavone C -glycoside, vicenin-2, which only occurred in trace amounts in var. americanum and was not detected in cv. Sacred. The major flavonoids in var. americanum and cv. Sacred, and also in all other species investigated for subgenus Ocimum , were flavonol 3- O -glucosides and 3- O -rutinosides. Many species in subgenus Ocimum also produced the more unusual compound, quercetin 3- O -(6″- O -malonyl)glucoside, and small amounts of flavone O -glycosides. The level of flavonol glycosides produced was reduced significantly in glasshouse-grown plants, but levels of flavone glycosides were unaffected. A single species investigated from subgenus Nautochilus , O. lamiifolium , had a different flavonoid glycoside profile, although the major compound was also a flavonol O -glycoside. This was identified as quercetin 3- O -xylosyl(1‴→2″)galactoside, using NMR spectroscopy. The species investigated from subgenus Gymnocimum , O . tenuiflorum (= O. sanctum ), was characterised by the accumulation of flavone O -glycosides. These were isolated, and identified as the 7- O -glucuronides of luteolin and apigenin. Luteolin 5- O -glucoside was found in all nine species of Ocimum studied, and is considered to be a key character for the genus.

The chemotaxonomic significance of two bioactive caffeic acid esters, nepetoidins A and B, in the Lamiaceae.

A survey of leaf surface constituents in the family Lamiaceae using HPLC with diode array detection revealed the presence of two characteristic phenolic compounds in many species. The distribution of these phenolics in the Lamiaceae was found to be of taxonomic significance, as they were present in the great majority of species investigated for the subfamily Nepetoideae, including representatives of the well-known genera of culinary herbs, mint, rosemary, sage, thyme and basil. In contrast, they were absent from species of the other subfamilies of Lamiaceae studied and from the related families Verbenaceae, Scrophulariaceae, Acanthaceae and Buddlejaceae. The compounds were isolated from Plectranthus crassus and identified by NMR spectroscopy as the known caffeic acid esters (Z,E)-[2-(3,5-dihydroxyphenyl)ethenyl] 3-(3,4-dihydroxyphenyl)-2-propenoate and (Z,E)-[2-(3,4-dihydroxyphenyl)ethenyl] 3-(3,4-dihydroxyphenyl)-2-propenoate, for which the trivial names nepetoidins A and B are proposed. The presence of this pair of caffeic acid esters adds another character to the chemical, palynological and embryological features distinguishing the Nepetoideae from the other subfamilies of Lamiaceae and related families, and supports the view that the Nepetoideae are a specialised and monophyletic group within the family. Nepetoidin B was shown to have a greater antioxidant activity than gallic, rosmarinic and caffeic acids, and showed activity as an insect phagostimulant. Both compounds were antifungal.

Acacetin glycosides as taxonomic markers in Calamintha and Micromeria

A new acetylated flavone glycoside, acacetin 7-O-[6-O-acetylglucosyl(1-->2)]rhamnosyl(1-->6)glucoside, has been isolated from the leaves of Calamintha glandulosa together with the known compound acacetin 7-O-rhamnosyl(1-->6)glucoside. The occurrence of these flavonoids in the closely related genera Satureja, Micromeria, Acinos and Clinopodium indicates that their distribution may be of taxonomic significance.

External leaf flavonoids of Thymus species from Macedonia

External flavonoids of 40 Macedonian species and infraspecific taxa of Thymus, belonging to sections Marginati, Pseudothymbra and Serpyllum, were studied by HPLC combined with diode array detection and atmospheric pressure chemical ionisation mass spectrometry. Nineteen different flavones were identified and the most common and abundant compound was 5,6-dihydroxy-7,3′,4′-trimethoxyflavone. Most species also produce surface flavanones, including eriodictyol, naringenin and isosakuranetin. The external flavonoid profiles found in species of Thymus provide useful additional taxonomic characters at various different levels of classification.