Isomer composition of tocopherols in seabuckthorn (Hippophae rhamnoides L.) seeds in forest-steppe area of Altai territory

Estimation of tocopherol isomers composition in seed oil of seabuckthorn (H. rhamnoides ssp. mongolica) varieties is represented. It has been established that α-tocopherol is the dominant tocopherol in the lipids of the seabuckthorn seeds, the mean content of which for two years has been ranged from 2.1 (Dar Katuni) to 4.8 mg/100 g (Yantarnaya). In general within the evaluated group of subspecies, the mean content of α- tocopherol was determined at 3.5±0.3 mg/100 g. β-, γ- and δ-tocopherols were characterized by low content, accumulating an average for two years at 0.5±0.1, 1.3±0.1 and 0.7±0.3 mg/100 g, respectively.

Diversity, isomer composition, and design of combinatorial libraries of tetrapyrrole macrocycles

Combinatorial libraries of substituted tetrapyrrole macrocycles, which can now be prepared via a variety of approaches, typically are rich in isomers. Terminology for describing such isomers (due to distinct patterns of peripheral substituents) is delineated in several illustrative examples. A hierarchical relationship exists of molecular formula, condensed formula(s) of substituents, set(s) of pyrrole collocates (conveying each pair of β-pyrrolic substituents), and isomers of substituted tetrapyrrole macrocycles. Isomers with identical pyrrole collocate sets can arise owing to distinct positions or orientations of the (homo- or hetero-substituted) pyrrolic units in a macrocycle. Consideration of a handful of virtual combinatorial libraries illustrates tradeoffs of library size, chemical richness, and isomeric content. As one example, octa-derivatization of a tetrapyrrole scaffold with eight reactants A–H affords 2,099,728 members (99.7% isomers, 82,251 pyrrole collocate sets, and 6,435 condensed formulas) whereas the reversible self-condensation of four pyrroles that bear the same eight entities (AB, CD, EF, GH) affords 538 members (93.5% isomers, 35 pyrrole collocate sets, and 35 condensed formulas). Derivatization affords all combinations and permutations whereas self-condensation of substituted pyrroles carries collocational restrictions. Understanding such tradeoffs and the structural origin of isomerism are important aspects in the design of tetrapyrrole combinatorial libraries.