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By a comparative thin layer chromatographic screening of the methanol-soluble leaf exudates from more than 400 Aloe plants (183 species), 5-hydroxyaloin A was identified in 20 species. Whilst 13 of the 20 species revealed interindividual variations concerning to the occurrence of 5-hydroxyaloin A, this anthrone-C-glucosyl was unambiguously detected in each individual of 6 Aloe species. In the leaf exudates from A. marlothii Berger 5-hydroxyaloin A was only traceable in the aloin-containing chemivars. The complete anthrone-C-glucosyl pattern of these 7 clearly characterized species has been determined additionally by qualitative and quantitative high performance liquid chromatography: The results obtained demonstrate that 5-hydroxyaloin only occurs in the more stable A-configuration (10 R, 1′S), thus being till now the only anthrone-C-glycosyl which has not been found as diastereomeric pair genuinely in plants. As well, 5-hydroxyaloin A characterizes a quantitatively significant hydroxylating pathway in biosynthesis of anthranoids. It is discussed as a chemotaxonomic marker of the genus Aloe, especially of the sections Pachydendron and Eualoe.
The accumulation and distribution of characteristic secondary products in the different organs of an Aloe plant (A. succotrina Lam.) were studied by high performance liquid chromatography for the first time. In the leaves of the Aloe plant, only anthrone-C-glycosyls of the 7-hydroxyaloin type and, for the first time in plant material, the free anthraquinone 7-hydroxyaloeemodin were found. In contrast to previous reports on the distribution of secondary products in Aloe plants, anthrone-C-glycosyls were also detected in flowers, bracts and the inflorescence axis of the species examined. Aloesaponol I, a tetrahydroanthracene aglycone, was only present in the underground organs and in the stem. The 2-alkylchromone-C-glucosyl aloeresin B showed no specific occurrence as it was found in every type of organ. Based on these results and the findings of recent studies on Aloe roots and flowers, a distribution scheme of polyketide types in the Aloe plant was established. It suggests a separate and independent anthranoid metabolism for underground Aloe organs and stem on the one hand, and for leaves and inflorescence organs on the other hand. In the latter structures anthranoid metabolism seems to be additionally compartmentalized as the anthranoid pro files of inflorescence organs and leaves differ in two points relevant to anthranoid biosynthe sis: firstly, the occurrence of anthrone aglycones and secondly, the individual content of corresponding anthrone-C-glucosyl diastereomers.