- Monomeric and dimeric stilbenoids from the orchid Dendrobium amplum
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Amplumthrin, a new dimeric 9,10-dihydrophenanthrene derivative, was isolated from the orchid Dendrobium amplum which also afforded the known 9,10-dihydrophenanthrene dimer flavanthrin and the monomeric stilbenoids gigantol, batatasin III, its 3′-O-methyl ether and 3,3′-O,O-dimethyl ether, 2,7-dihydroxy-3,4,6-trimethoxyphenanthrene and its 9,10-dihydro derivative, 2,3,7-trihydroxy-4,6-dimethoxyphenanthrene and its 9,10-dihydro derivative and coelonin. The structure of amplumthrin was established as 2,2′,7,7′-tetrahydroxy-3,3′,4,4′,6,6′-hexamethoxy- 9,9′,10,10′-tetrahydro-1,1′-biphenanthryl from various spectral and chemical evidence. The structure of amplumthrin was finally confirmed by regioselective biomimetic synthesis of the compound from its monomeric congener 2,7-dihydroxy-3,4,6-trimethoxy-9,10-dihydrophenanthrene by oxidative phenol-coupling reaction with CuCl(OH). TMEDA in very good yield (80%). Similar biomimetic synthesis of flavanthrin was also achieved in 82% yield from its monomeric congener coelonin using the same oxidant. The co-occurrence of amplumthrin and flavanthrin with their respective monomers in the same orchid Dendrobium amplum provides a strong circumstantial evidence in support of the proposed biogenesis of the naturally occurring biphenanthryl derivatives assumed to have arisen from their corresponding monomers through enzymatic oxidative phenol-coupling reaction.
- Majumder,Rahaman, Burhanur,Roychowdhury, Mausumi,Dhara
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experimental part
p. 192 - 199
(2009/06/23)
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- Novel oxidative phenol-coupling reaction with phosphomolybdic acid on silica gel support: Regioselective biomimetic synthesis of dimeric phenanthrene derivatives
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Biomimetic synthesis of the naturally occurring dimeric phenanthrene derivatives, cirrhopetalanthrin (3a) and flavanthrin (7a), and their structural analogues 3c, 3e, 5a and 7c was achieved in very high yields by regioselecxtive oxidative coupling of their respective phenolic monomers 2a, 6a, 2c, 2e, 4a and 6c with phosphomolybdic acid on a silical gel support. Unlike coelonin (6a) and lusianthridin (6c), 2,7-dihydroxy-3,4,6-trimethoxy-9-10-dihydrophenanthrene (6e) gave, on similar oxidation, the phenanthrene dimer 3e, instead of the expected 9,10-dihydrophenanthrene dimer 7e. β-Naphthol afforded the corresponding 1,1'-dimer 1a in almost quantitative yield. The structures of the new dimeric compounds were established from various spectral data of the compounds and their respective acetyl derivatives.
- Majumder,Basak
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p. 8601 - 8610
(2007/10/02)
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