Chromones and anthrones from Aloe marlothii and Aloe rupestris

A phytochemical investigation of the leaf exudate of Aloe marlothii has resulted in the isolation of a new chromone (7-O-methylaloeresin A) and a new anthrone (5-hydroxyaloin A 6'-O-acetate). Furthermore 7-O-methylaloesin was isolated as a natural product for the first time from the leaf exudate of Aloe rupestris. The structure elucidation of these compounds was based on spectral data including 2D NMR. The chemotaxonomic value of 7-O-methylaloesin in Aloe series Asperifoliae and section Pachydendron is discussed.     

The occurrence and taxonomic distribution of the anthrones aloin, aloinoside and microdontin in Aloe

A chemotaxonomic survey of 380 species of Aloe indicated the presence of the anthrone isomers aloin A and B together with the aloinoside isomers and microdontin A and B in 36 (10%) species of Aloe. This group, referred to as the microdontin chemotype, is thus characterised by a combination of exudate compounds and not merely a single phytochemical marker, implying taxonomic significance of leaf exudate compounds. The 36 representatives of the group occupy disparate taxonomic positions in the largely artificial hierarchy of the present classification system. Although many of the species have previously been considered as related (based on macromorphology only), a large number of species have not been associated with one another before. The chemical profiles and leaf exudate compositions of the species are presented, followed by a brief summary of the morphological diversity. Whilst conceding the possibility of convergent evolution, the geographical distribution of the species and thoughts on possible relationships between the taxa are discussed.     

6'-O-Coumaroylaloesin from Aloe castanea--a taxonomic marker for Aloe section Anguialoe

The structure of 6'-O-coumaroylaloesin [2-acetonyl-8-(6-O-coumaroyl-beta-D-glucopyranosyl)-7-hydrox y-5-methylchromone], a mono-ester chromone derivative in which only the 6-position of the glucosyl moiety is esterified, was determined by spectroscopic methods. The compound is a unique chemotaxonomic character restricted to the six species in Aloe section Anguialoe.     

The chemotaxonomic significance of the phenyl pyrone aloenin in the genus Aloe

The phenyl pyrone, aloenin was positively identified in 16 species in a greater chemotaxonomic study on 380 species of Aloe. A large number of species have previously been suggested to be related on the basis of their macromorphological characters. The leaf exudate composition of the 16 species are presented together with a summary of the salient morphological characters. The possible taxonomic relationships between aloenin producing species, not previously thought to be associated with one another are discussed and illustrates the need to explore additional characters of taxonomic value in this large genus of ca. 420 species where no natural classification system exists.     

The phytochemical profile and identification of main phenolic compounds from the leaf exudate of Aloe secundiflora by high-performance liquid chromatography-mass spectroscopy

The phytochemical profile of Aloe secundiflora (Aloeaceae) and the identity of eight major compounds, including the two main constituents, have been determined from the leaf exudate of this ethnoveterinary used species from Kenya and Tanzania. Analytical HPLC-MS studies of the exudate have revealed that it comprises a mixture of phenolic compounds, mainly anthrones (aloenin, aloenin B, isobarbaloin, barbaloin and other aloin derivatives), chromones and phenylpyrones with a low content of polysaccharides and aliphatic compounds. The high percentage of anthrones in the exudate could provide a first line of evidence for the use of the plant in ethnoveterinary practices.     

Growth, soluble carbohydrates, and aloin concentration of Aloe vera plants exposed to three irradiance levels

Research was conducted on Aloe vera, a traditional medicinal plant, to investigate the effects of light on growth, carbon allocation, and the concentrations of organic solutes, including soluble carbohydrates and aloin. The plants were vegetatively propagated and grown under three irradiances: full sunlight, partial (30% full sunlight), and deep shade (10% full sunlight) for 12-18 months. After 1 year of growth, five plants from each treatment were harvested to determine total above- and below ground dry mass. Four plants from the full sunlight and the partial shade treatments were harvested after 18 months to assess the soluble carbohydrate, organic acid and aloin concentrations of the clear parenchyma gel and the yellow leaf exudate, separately. Plants grown under full sunlight produced more numerous and larger axillary shoots, resulting in twice the total dry mass than those grown under partial shade. The dry mass of the plants grown under deep shade was 8.6% that of plants grown under full sunlight. Partial shade increased the number and length of leaves produced on the primary shoot, but leaf dry mass was still reduced to 66% of that in full sunlight. In contrast, partial and deep shade reduced root dry mass to 28 and 13%, respectively, of that under full sunlight, indicating that carbon allocation to roots was restricted under low light conditions. When plants were sampled 6 months later, there were only minor treatment effects on the concentration of soluble carbohydrates and aloin in the leaf exudate and gel. Soluble carbohydrate concentrations were greater in the gel than in the exudate, with glucose the most abundant soluble carbohydrate. Aloin was present only in the leaf exudate and higher irradiance did not induce a higher concentration. Limitation in light availability primarily affected total dry mass production and allocation, without substantial effects on either primary or secondary carbon metabolites.     

Three oxanthrones from Aloe littoralis

The leaf exudate of Aloe littoralis yielded, in addition to the known 10-hydroxyaloin B, two new C-glucoside oxanthrones namely 10-hydroxy-15-O-(2R,3S-nilyl)(6′-O-acetyl)aloin B (littoraloin) and 10-hydroxy-15-O-(2R,3S- nilyl)aloin B (deacetyllittoraloin). Their structures were determined by spectroscopic methods as well as by conversion to the known 10-hydroxyaloin B and nilic acid.     

Identification of major metabolites in Aloe littoralis by high-performance liquid chromatography-nuclear magnetic resonance spectroscopy

Examination of the leaf exudate of the South African species Aloe littoralis by reversed-phase HPLC revealed the presence of two major metabolites. The identification of the two compounds without isolation was attempted by HPLC-NMR based on separation using a C18 column eluting with a deuterium oxide:acetonitrile solvent gradient and an inverse HPLC-NMR probe. For each compound, one-dimensional proton spectra, and two-dimensional homonuclear COSY and TOCSY, and heteronuclear HSQC and HMBC, spectra were collected. On the basis of the data obtained, the metabolites were characterised as 10-hydroxyaloin B and deacetyllittoraloin.     

Anthraquinone,anthrone and phenylpyrone components of Aloe nyeriensis var. kedongensis leaf exudate

The leaf exudate of Aloe nyeriensis var. kedongensis yielded six compounds which were identified on the basis of spectral data and inter-conversions as two groups of three allied compounds. These were (a) 4-methoxy-6(2′,4′-dihydroxy-6′- methylphenyl)-pyran-2-one, its 2′-O-β-D-glucopyranoside (aloenin) and the 2″-O-p-coumaroyl ester of aloenin, (b) the anthracene derivatives l,2,8-trihydroxy- 6-methylanthraquinone (nataloe-emodin), its 2-O-β-D-glucopyranosyl ester and the corresponding 10-C -β-D-glucopyranoside nataloin.     

Distribution and chemotaxonomic significance of flavonoids inAloe (Asphodelaceae)

A chemotaxonomic study of practically all the species of the genusAloe showed that flavonoids occur as major compounds in 31 out of a total of 380 species investigated. Flavanones and dihydroflavonols are present in the exudate of species inAloe ser.Rhodacanthae andSuperpositae and also in a number of the endemic species from Madagascar. Flavones occur as the only major compound in the leaf extracts of the sects.Leptoaloe andGraminialoe. In ser.Macrifoliae and inLomatophyllum, the sister genus ofAloe, isovitexin co-occurred with theC-glucosylanthrone aloin. The chemotaxonomic implication of these results are discussed together with the significance of the taxonomic and chemogeographical distribution of flavonoids inAloe. With a few rare exceptions, the leaf compounds from two different biogenetic pathways (polyketide pathway and flavonoid pathway) are mutually exclusive. Since flavonoids are restricted to the basal groups inAloe, we conclude that flavonoids are plesiomorphic characters inAloe reflecting ancient phylogenetic and biogeographic links.     

Cape aloes—A review of the phytochemistry,pharmacology and commercialisation of Aloe ferox

Aloe ferox Mill. (= A. candelabrum A. Berger), commonly known as the bitter aloe or Cape aloe, is a polymorphic species indigenous to South Africa. The plant has been used since ancient times as a generic chemopreventive and anti-tumour remedy in folk medicine and it has a well-documented history of use as a laxative. In addition to the plethora of traditional medicinal uses, A. ferox has recently gained popularity as an ingredient in cosmetic formulations and food supplements. Anti-oxidant, antimicrobial, anti-inflammatory, anticancer and antimalarial activities, etc. have been reported. In addition, the ability of Cape aloes to enhance the transport of poorly permeable drugs has enjoyed recent research interest. Due to its medicinal and commercial importance it has been a popular research topic for natural product scientists who have isolated several chromones and anthrones from the leaf exudate and finished product (bitters). A summary of the historical and modern day uses, commercialisation, chemical composition and biological properties of this coveted ethnomedicinally and commercially important species is presented.     

芦荟属植物叶内蒽醌类物质的分布与其化学防御的关系

芦荟属植物是一类生长在干旱或半干旱沙漠环境的肉质植物,木立芦荟和海藻芦荟的肉质叶的植物研究结果表明,叶内含高浓度的芦荟素,高那特芦荟素,芦荟苦素和芦荟宁等蒽醌类物质,其中,海莱芦荟整叶的蒽醌类物质总含量占其泌出物干重的44．89％。两种芦荟叶内蒽醌类物质的分布有共同的规律,即幼叶的含量高于老叶;叶上部的含量高于中,基部,叶缘则高于叶的中央。但由于木立芦荟和海莱芦荟的个体形态不同,蒽醌类物质的分布在种间还存在各自的特点,根据实验结果推测,蒽醌类物质在芦荟属植物体内的累积和分布与其化学防御机制有关。     

<Emphasis Type="Italic">In vitro</Emphasis> antileishmanial activity of <Emphasis Type="Italic">Aloe vera</Emphasis> leaf exudate: A potential herbal therapy in leishmaniasis

Aloe vera has wide spread use in health products, and despite several reports on the whole plant and inner gel, little work has been performed on the leaf exudate. Our aim was to evaluate the in vitro efficacy of Aloe vera leaf exudate (AVL) in leishmaniasis. Irrespective of the disease manifestation, promastigotes from strains responsible for cutaneous, mucocutaneous, and visceral leishmaniasis were susceptible to AVL and their IC₅₀ ranged from 100 to 180 μg/ml. In axenic amastigotes cultured from a L. donovani strain 2001 responsible for visceral leishmaniasis, the IC₅₀ was 6.0 μg/ml. AVL caused activation of host macrophages evident by an increased release of members of reactive oxygen species that was attenuated by preincubation with free radical scavengers. Collectively, our data indicates that AVL, via its direct leishmanicidal activity which can be further enhanced by activation of host macrophages, is an effective antileishmanial agent meriting further pharmacological investigations.     

Secretory tissues in the East African shrubby aloes

Examination of Aloe leaf sections revealed the presence of three types of cells at the phloem pole of the vascular bundles, aloin cells, outer bundle sheath cells and fibres. Three species contain fibres alone and produce a sparse exudate with few components staining purple with Fast Blue B on thin-layer chromatograms. The majority of species have aloin cells of various sizes and in the tetraploid species these produce a copious exudate containing anthraquinone and chromone derivatives. It is suggested that the aloin cells act as storage tissue and that the compounds are synthesized in the surrounding layer of cells of smaller diameter, many of which can be seen to contain globules of unknown constitution. Anatomical observations support the idea that the shrubby tetraploid Aloe species are derived from a form similar to the diploid Aloe morijensis. Two forms of this species have been described, one with fibres only and few exudate components and another with both fibres and aloin cells and an exudate containing compounds of the tetraploid species. A line of diploid plants similar in anatomy and chemistry to the first form is represented by A. fibrosa and A. babatiensis while a line of tetraploids with affinities to the second form is represented by A. nyeriensis, A. cheranganiensis, A. elgonica, A. dawei and A.yavellana.     

芦荟维管束的结构与芦荟素积累的相关性

应用半薄切片、组织化学、荧光显微镜观察和薄层层析 (TLC)相结合的方法研究了中华芦荟 (Aloeve-ra L.var.chinensis)、木立芦荟 (Aloe arborescens)叶和茎内维管束的结构及其与芦荟素积累的关系。结果表明 ,木立芦荟叶内维管束和中华芦荟叶内外轮的维管束中有大型韧皮薄壁细胞 ,而木立芦荟茎和中华芦荟叶中内轮维管束无大型韧皮薄壁细胞。组织化学结果表明 ,用醋酸铅处理过的上述材料 ,大型韧皮薄壁细胞内出现沉淀物 ;在荧光显微镜下经蓝光激发 ,大型韧皮薄壁细胞发出桔黄色荧光 ,都显示出芦荟素反应。薄层层析(TLC)结果证明 ,木立芦荟和中华芦荟叶含有大型韧皮薄壁细胞的维管束都含芦荟素 ,而木立芦荟茎及中华芦荟叶中内轮维管束都不含芦荟素。为此 ,维管束中的大型韧皮薄壁细胞与芦荟素的积累密切相关 ,维管束中是否有大型韧皮薄壁细胞可作为判断是否含有芦荟素的解剖学指标。     

Protein Extraction From Leaves of Aloe vera L., A Succulent and Recalcitrant Plant, for Proteomic Analysis

An improved method for extracting proteins from leaf tissues of Aloe vera L., a recalcitrant plant species, for proteomic analysis is presented. In this protocol, the following critical components are included. A washing step is added prior to homogenization of the tissue to eliminate contaminants, and a concentrated 2× extraction buffer (pH 7.5) is used to increase protein yield. Compared to classical trichloroacetic acid–acetone and phenol extraction methods, this novel protocol has yielded two-dimensional electrophoresis gels with minimal (if any) streaking and provided high-quality protein samples. This protocol is expected to be applicable to other recalcitrant plant tissues.     

The chemotaxonomic value of the diglucoside anthrone homonataloside B in the genus Aloe

The chemotaxonomic value of the only known diglucoside anthrone from Aloe, homonataloside B, is discussed. This compound has been detected in only 14 species in a chemotaxonomic survey of 380 Aloe species. The homonataloside B-accumulating species are only found in Africa with none of the Malagasy endemics producing this compound. A summary of the morphological variation is presented together with the taxonomic distribution of this unique anthrone. The representatives of this distinct chemotype occupy disparate positions in the largely artificial hierarchy of the present classification system. Species included in this chemotype provide chemical evidence of hybridisation in Aloe.     

Isolation and characterization of novel protein with anti-fungal and anti-inflammatory properties from Aloe vera leaf gel

The Aloe protein of 14 kDa from the Aloe vera leaf gel was isolated by an ion exchange chromatography using DEAE-cellulose and CM-cellulose column. The purified Aloe protein exhibited a potent anti-fungal activity against Candida paraprilosis, Candida krusei and Candida albicans. In addition, the purified Aloe protein also showed an anti-inflammatory property against pure lipoxygenase and cyclooxygenase-2 with 84% and 73% inhibition, respectively, and was verified by binding with these proteins by real time method by the phenomenon of surface plasmon resonance. This Aloe protein is a novel protein possessing antifungal and anti-inflammatory properties and thus sets a platform to be used as a medicinal plant product.     

芦荟属3种植物不同叶龄、不同部位叶内蒽醌类物质含量及其变化的研究

用植物化学技术研究了3种芦荟属植物不同叶龄和不同部位叶中蒽醌类物质的含量及其变化。结果表明,被研究的芦荟属3种植物叶中主含的蒽醌类物质有：芦荟素或高那特芦荟素,芦荟宁和芦荟苦素。其中,中华芦荟和木立芦荟主含芦荟素;海莱芦荟主含高那特芦荟素。叶各部位详细分析的结果表明,蒽醌类物质在植株上部的嫩叶中的含量要高于下部老叶;同一叶中,叶尖高于叶中部,叶基含量最低;而叶缘含量高于叶的中央部分。在同一叶的横切面上,蒽醌类物质的含量在维管柬区最高,同化薄壁组织部分次之,储水组织部分最低。芦荟属植物在同一个植物体不同的叶之间,以及同一叶不同的位置间有规律的累积蒽醌类物质有重要的生物学意义。它是保证芦荟属植物在原产地的干旱和半干旱生活环境中得以良好生存的适应反应和化学防御机制。     

Comparative chromatographic patterns of leaf exudate components from Aloe Section Pachydendron Haw

Leaf exudates from individuals of 29 species included in Aloe Section Pachydendron have been separated by TLC and HPLC to reveal their phenolic components. All the zones are described by their chromatographic behaviour and UV absorption properties, but not all can be identified as known compounds so are distinguished by an arbitrary code. Section Pachydendron has been shown to be chemically heterogeneous akhough there are some correlations between species said to be taxonomically related. Without attaching taxonomic significance four chemical groupings can be discerned: (1) species in which chromones are prominent; (2) species in which andirone and anthraquinone glycosides are prominent; (3) species containing mainly purple-staining phenolic compounds; and (4) species with few leaf exudate phenolic compounds. This survey emphasizes the uncertain taxonomy of the Section and the need for more extensive collection and analysis.