Dendrobium

The trimer famesyl pyrophosphate (35), in addition to serving as a pregenitor of steroids via squalene (114), is also the pregenitor of the compounds known as sesquiterpenes. It has been suggested that famesyl pyrophosphate (88) similarly serves as the carbon backbone of alkaloids such as deoxynuphatidine (120) ftom Nupharjapomcum (Nymphaceae) (water hhes) and dendrobine (121) Dendrobium nobikl indl. (Orchidaceae) (Table 11). 

Dendrobium crumenatum Sw., or pigeon orchid, is an epiphyte orchid that grows in India, China, the Philippines, and Malaysia. The stem is 4 mm in diameter and the bulbs are 2-3 cm around. The leaves are 7 X 1.3 cm, linear, and fleshy. The petiole is 4Xl mm. The flowers are white (Fig. 60). 

The dopaminergic potential of the Dendrobium species is, to date, open for exploration. An interesting feature of the Dendrobium species is their ability to elaborate sesquiterpene alkaloids, the chemical structure of which resembles the one of strychnine. One such alkaloid is dendrobine, which is widespread in the genus. Kudo et al. noted that dendrobine, isolated from Dendrobium nobile, exhibits a strychnine-like presynaptic inhibition in frog spinal cord (64). 

Cycloaddition reactions of furans are still widely used as key steps in the construction of complex molecules including natural products. As an example, the intramolecular Diels-Alder cycloaddition of 2-amido substituted furans provides a useful tool for the synthesis of fused, nitrogen-containing poly-heterocycles. Thus, thermolysis of 3-substituted amidofuran produces tricyclic indolinone 39 as a 2 1 mixture of diastereomers via amidofuran cycloaddition-rearrangement methodology, which serves as a key intermediate in the total synthesis of ( )-dendrobine, a major component of the Chinese ornamental orchid Dendrobium nobile . 

The pyrrolidine ring is part of numerous natural products, and we have restricted the field to those alkaloids that contain an isolated pyrrolidine ring. We have thus excluded the so-called Sceletium (mesembrine) and Dendrobium (den-drobine) alkaloids, which have also been reviewed (3-5). The pyrrolidine ring is frequently encountered in proline residues of cyclopeptide alkaloids these have been reviewed already (7) and will not be discussed here. 

New sources of hygrine are the roots of Nicandra physaloides (L.) Gaertn. (Solanaceae) (9, JO), Dendrobium chrysanthum Wall. (Orchidaceae) (11), and Cochlearia arctica Slecht (Cruciferae) (12). Hygroline was also isolated from this latter source as well as from Carallia brachiata (Lour.) Merr. (Rhi-zophoraceae), a plant from eastern Asia, New Guinea, and Queensland (13), and... 

N-cis- and N-frans-cinnamoylnorcuscohygrine (10 and 11) (cis- and trans-dendrochrysines) have been found in the orchid Dendrobium chrysanthum Wall. (37). The structure determination of these products was based on IR, UV, and NMR spectra for the cinnamoyl residue and on mass spectrometry (N-methylpyr-rolidin-2yl group). 

Shihunine (57), previously isolated from Dendrobium lohohense Tang and Wang (99, 100) andD. pierardii Roxb. (Orchidaceae) (101), has been found as a racemate in Banisteriopsis caapi Morton (102). This plant species also contained the optically active dihydroshihunine 58, a compound only known before as a racemic synthetic material. Both 57 and 58 were identified by direct comparison with authentic samples. The absolute configuration of (+)-(58) was determined as 25 by comparison of the CD spectra of 58 and of the a-phenylethylamines (102). 

The anthocyanin composition of flowers has also been frequently investigated by chromatographic methods. Acylated anthocyanins and flavonols have been extracted from the flowers of Dendrobium cv. Pompadour and separated by TLC and RP-HPLC techniques. Fresh flowers (approximately. 1 kg) were extracted with 101 of methanol-acetic acid-water (4 1 5, v/v), and the extract was concentrated and analysed by preparative and analytical RP-HPLC using ODS columns (150 X 19 mm i.d. and 250 X 4.6 mm i.d.) at 40°C. The gradient consisted of methanol-water-acetic acid in various volume ratios. Flow rates were 4 and 1 ml/min for preparative and analytical separations, respectively. Cyanidin 3- (6-malonylglucoside)-7,3 -di(6-synapilglucoside) and the demalonyl derivative were detected in the flowers [261],... 

C.A. Williams, J. Greenham, J.B. Harborn, J.-M. Kong, L.- S. Chia, N.-K. Goh, N. Saito, K. Toki and F. Tatsuzawa, Acylated anthocyanins and flavonols from purple flowers of Dendrobium cv. Pompadour . Biochem. Syst. Ecol. 30 (2002) 667-675. 

Aduncin, a picrotoxane sesquiterpenoid isolated from Dendrobium aduncum, has been assigned structure (147) on the basis of its spectroscopic properties and their similarity to those of a- and /3-dihydropicrotoxinin (148). A full paper dealing with the previously reported synthesis of 4-epidendrobine (149) has been published (cf. Vol. 7, p. 74). 

Williams, C.A. et al., Acylated anthocyanins and flavonols from purple flowers of Dendrobium cv. Pompadour , Biochem. Syst. Ecol., 30, 667, 2002. 

Saito, N. et al.. An acylated cyanidin glycoside from the red-purple flowers of Dendrobium, Phytochemistry, 37, 245, 1994. 

Dendrobium nobile Lindl. Shi Dou (Orchid) (stem) Dendrobine.50 Analgesic, hyperglycemic, hypotensive, hypothermic. 

Dendrobium nobile Lindl., Epidendrum monile Thunb. 

The [2.3.3]cyclazidine derivative crepidine (222), which is found in Dendrobium species together with indolizidine alkaloids, has been treated in Section 3.08.8.2. 

Dendrobine at a dose of 3 X 10-5 M reduced the dorsal root potential and reflex. It provoked a mild hyperpolarization in both dorsal and ventral roots of frog isolated spinal cord. It affected the (3-alanine- and taurine-induced depolarization of primary afferent terminals and reversibly blocked the presynaptic inhibition caused by antidromic conditioning stimulation of the ventral root potential induced by repetitive antidromic stimulation of ventral root and lowered maximum. It would be interesting to learn whether further research of the Dendrobium species discloses any alkaloid interfering with the glycinergic system, an aspect discussed under the following heading. 

C. pwpureum, Cyrtorchis montierae, C. praetermissa, Dendrobium sp., Dendrobium acwninalissimum, Diaphananthe fragranlissima,... 

In the spectra of [200] and [201] (synthetic intermediates in the synthesis of Dendrobium alkaloids) the shifts of the 2-protons are... 

Dendrobium Alkaloids.—A third synthesis of shihunine, the principal base of several Dendrobium spp., has been reported. It involves allowing the dilithio-anion (12) to react with l-methyl-2-pyrrolidone (13), to yield ( )-shihunine (14) in 23% yield.11 Full experimental details pertaining to a synthesis of ( )-dendrobine, reported briefly earlier, have been described.12... 

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