Electron ionization (EI) mass spectra of some 3,4-disubstituted-1,2,4- oxadiazin-5-ones and-thiones and 3,5-disubstituted 1,2,4-oxadiazin-6-ones

The EI mass spectra of 3,4-disubstituted-1,2,4-oxadiazin-5-ones 1-6 and -thiones 7,8 and 3,5-disubstituted 1,2,4-oxadiazin-6-ones 9,10 were recorded and their fragmentation pathways solved and compared with each other. The fragmentation routes of 5-ones and 5-thiones do not differ very much from each other but compounds 9 and 10 behave differently as could be expected based on their lactone type structures. Only compounds 4-6 exhibit a loss of CO and compound 7 a loss of NO. The loss of a benzyl group dominates the behaviour of compounds 1 and 2 which showed only few additional fragmentations. Some earlier data on some 3,4-disubstituted-1,2,4-diazin-5-ones 11-13 and -thiones 14,15 have been reanalyzed and discussed in further detail

Enthalpies of Combustion and Formation of Severely Crowded Methyl-Substituted 1,3-dioxanes. The Magnitudes of 2,4- and 4,6-diaxial Me,Me-Interactions and the Chair-2,5-twist Energy Difference

Enthalpies of combustion of 2,2-trans-4,6- (1) and 4,4,6,6-tetramethyl- (2) and 2,4,4,6,6- (3) and 2,2,4,4,6-pentamethyl-1,3-dioxanes (4) were determined to estimate their enthalpies of formation in the gas phase. By comparing the latter with the corresponding enthalpies estimated based on the various bond–bond interactions allowed to determine the chair–2,5-twist energy difference (ΔHCT = 29.8 kJ mol–1) for 1 since C-13 shift correlations indicate that it escapes to the 2,5-twist form where the 2-methyl groups are isoclinal and 4- and 6-methyl groups pseudoequatorial to avoid syn-axial interactions. Compounds 2 and 3 in turn give the values 21.0 and 21.6 kJ mol–1 for the 4,6-diaxial Me,Me-interaction. Finally compound 4, which retains the chair conformation to avoid pseudoaxial interactions in the twist forms gives the value 19.5 kJ mol–1 for the 2,4-diaxial Me,Me-interaction indicating that its chair form appears to be somewhat deformed

High-performance liquid chromatographic analysis of phlorotannins from the brown alga Fucus Vesiculosus

Separating individual compounds by HPLC represents an effective method for the detection and quantification of phenolic compounds and has been widely utilised. However, phlorotannins are commonly quantified using colorimetric methods, as the total amount of the whole compound group. In the present paper the separation of a set of individual soluble phlorotannins from the phenolic crude extract of Fucus vesiculosus was achieved by HPLC with UV photodiode array detection. Different gradient programs for reversed- and normal-phase HPLC methods were developed and tested. Normal-phase (NP) conditions with a silica stationary phase and a mobile phase with a linear gradient of increasing polarity were found to separate 16 individual components of the phenolic extract. The suitability of the NP-HPLC method for mass spectrometric application was preliminarily tested. Sample preparation was found to be a critical step in the analysis owing to the rapid oxidation of phlorotannins; ascorbic acid was used as an antioxidant

Changes in leaf trichomes and epicuticular flavonoids during leaf development in three birch taxa

• Background and Aims Changes in number of trichomes and in composition and concentrations of their exudates throughout leaf development may have important consequences for plant adaptation to abiotic and biotic factors. In the present study, seasonal changes in leaf trichomes and epicuticular flavonoid aglycones in three Finnish birch taxa (Betula pendula, B. pubescens ssp. pubescens, and B. pubescens ssp. czerepanovii) were followed. • Methods Trichome number and ultrastructure were studied by means of light, scanning and transmission electron microscopy, while flavonoid aglycones in ethanolic leaf surface extracts were analysed by high-pressure liquid chromatography. • Key Results Density of both glandular and non-glandular trichomes decreased drastically with leaf expansion while the total number of trichomes per leaf remained constant, indicating that the final number of trichomes is established early in leaf development. Cells of glandular trichomes differentiate before those of the epidermis and produce secreted material only during the relatively short period (around 1–2 weeks) of leaf unfolding and expansion. In fully expanded leaves, glandular trichomes appeared to be at the post-secretory phase and function mainly as storage organs; they contained lipid droplets and osmiophilic material (probably phenolics). Concentrations (mg g(−1) d. wt) of surface flavonoids decreased with leaf age in all taxa. However, the changes in total amount (µg per leaf) of flavonoids during leaf development were taxon-specific: no changes in B. pubescens ssp. czerepanovii, increase in B. pendula and in B. pubescens ssp. pubescens followed by the decline in the latter taxon. Concentrations of most of the individual leaf surface flavonoids correlated positively with the density of glandular trichomes within species, suggesting the participation of glandular trichomes in production of surface flavonoids. • Conclusions Rapid decline in the density of leaf trichomes and in the concentrations of flavonoid aglycones with leaf age suggests that the functional role of trichomes is likely to be most important at the early stages of birch leaf development

Comparative analysis of leaf trichome structure and composition of epicuticular flavonoids in Finnish birch species

The morphology, ultrastructure, density and distribution of trichomes on leaves of Betula pendula, B. pubescens ssp. pubescens, B. pubescens ssp. czerepanovii and B. nana were examined by means of light, scanning and transmission electron microscopy. The composition of flavonoids in ethanolic leaf surface extracts was analysed by high pressure liquid chromatography. All taxa examined contained both glandular and non‐glandular trichomes (short and/or long hairs) but differed from each other in trichome ultrastructure, density and location on the leaf. Leaves of B. pubescens were more hairy than those of B. pendula, but the latter species had a higher density of glandular trichomes. Of the two subspecies of B. pubescens, leaves of ssp. pubescens had more short hairs on the leaf surface and four times the density of glandular trichomes of leaves of ssp. czerepanovii, whereas, in the latter subspecies, short hairs occurred largely on leaf veins, as in B. nana. The glandular trichomes were peltate glands, consisting of medullar and cortical cells, which differed structurally. Cortical cells possessed numerous small, poorly developed plastids and small vacuoles, whereas medullar cells had several large plastids with well‐developed thylakoid systems and fewer vacuoles. In B. pubescens subspecies, vacuoles of the glandular cells contained osmiophilic deposits, which were probably phenolic, whereas in B. pendula, vacuoles of glandular trichomes were characterized by the presence of numerous myelin‐like membranes. The composition of epicuticular flavonoids also differed among species. The two subspecies of B. pubescens and B. nana shared the same 12 compounds, but five of these occurred only in trace amounts in B. nana. Leaf surface extracts of B. pendula contained just six flavonoids, three of which occurred only in this species. In summary, the structure, density and distribution of leaf trichomes and the composition of epicuticular flavonoids represent good taxonomic markers for Finnish birch species