- Dichlorodicyanoquinone Oxidations in the Indole Area. Synthesis of Crenatine
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The influence of temperature on the reaction of dichlorodicyanoquinone (DDQ) with 1,2,3,4-tetrahydro-β-carbolines has been explored.The DDQ oxidation of amide 2a, when performed at room temperature, gave 3a (3-acylindole)/4 (2-acylindole) in a ratio of ca. 1:1, while this was increased to 2:1 at 0 deg C and to ca. 5:1 at -78 deg C.This method for preparation of 4-oxo-β-carbolines has been employed for synthesis of the β-carboline alkaloid crenatine (11).In addition, treatment of the 4-oxotetrahydro-β-carboline (3b) with hydrazine gave 1-ethyl-4-amino-β-carboline (12) which should provide access to a series of 4-substituted β-carbolines.
- Cain, M.,Mantei, R.,Cook, J. M.
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- Synthetic studies of indoles and related compounds. XXVII. A new synthesis of crenatine from ethyl indole-2-carboxylate
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Crenatine (1a), which is a member of a new class of β-carboline alkaloids having an oxygen functionality at the 4-position, was synthesized starting from ethyl 1-benzylindole-2-carboxylate (12a) via cyclization of an elaborated C2-substituent to the 3-position of the indole nucleus and aluminum chloride-catalyzed debenzylation of the protected indolic nitrogen. 1-Ethyl-4-hydroxy-9-methyl-β-carboline (26b), a positional isomer of crenatine with regard to the methyl group, was also synthesized through the same methodology.
- Murakami,Yokoyama,Aoki,Suzuki,Sakurai,Shinohara,Miyagi,Kimura,Takahashi,Watanabe,Ohmoto
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p. 2189 - 2195
(2007/10/02)
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- DDQ Oxidations in the Indole Area. Synthesis of 4-Alkoxy-β-carbolines Including the Natural Products Crenatine and 1-Methoxycanthin-6-one
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The seven-step synthesis of the cytotoxic, antileukemic alkaloid 1-methoxycanthin-6-one (2b) is described.The pivotal steps are represented by the oxidation (DDQ, aqueous THF, room temperature) of 1-(methoxycarbonyl)-1,2,3,4-tetrahydro-β-carboline (10) to provide the 4-oxo-substituted derivative 14 in 78percent yield, and conversion of the 4-oxo analogue 7 into 4-methoxy-1-alkyl-β-carboline (23) via a methoxylation-oxidation process .This four-step, one-pot reaction has been shown to be general; 4-oxo-1,2,3,4-tetrahydro-β-carboline (18) was converted into the corresponding 4-methoxy-, 4-ethoxy-, 4-(allyloxy)-, and 4-(benzyloxy)-β-carbolines (19a-d, respectively) on heating in the appropriate alcohol in the presence of pTSA and a trialkyl orthoformate (Table II).The proposed mechanism for this intriguing transformation is outlined in Scheme IV.Execution of this process has also resulted in a four-step preparation of crenatine (1a), a 4-methoxy-1-ethyl-β-carboline alkaloid.Finally, steric and electronic parameters have also been successfully manipulated to direct the DDQ oxidation of 1,2,3,4-tetrahydro-β-carbolines to position 1, regiospecifically.The conversion of tetrahydro-β-carboline 25 into 2-acylindole 38 and benzamide 26 into 1-oxotetrahydro-β-carboline 27 (Table I), respectively, is in agreement with the proposed mechanism for this process.
- Hagen, Timothy J.,Narayanan, Krishnaswamy,Names, Jeffrey,Cook, James M.
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p. 2170 - 2178
(2007/10/02)
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- A NEW ROUTE TO 4-OXYGENATED β-CARBOLINES: THE TOTAL SYNTHESIS OF CRENATINE
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Crenatine, a new type of β-carboline alkaloid having an oxygen function at its C4-position, was synthesized using ethyl 1-benzylindole-2-carboxylate as a starting material via cyclization of C2-substituent to C3-position of indole nucleus and AlCl3-catalyzed debenzylation for N-protected indoles.
- Murakami, Yasuoki,Yokoyama, Yuusaku,Aoki, Chiyoko,Miyagi, Chiemi,Watanabe, Toshiko,Ohmoto, Taichi
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p. 875 - 878
(2007/10/02)
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- The Alkaloids of Picrasma javanica
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Extraction of Picrasma javanica Bl. (Simarubaceae) has yielded two new β-carboline alkaloids, 1-ethenyl-4-methoxy-9H-pyrido-indol-5-ol (5-hydroxydehydrocrenatine) (4) and 1-ethyl-4-methoxy-9H-pyridoindol-5-ol (5-hydroxycrenatine) (5), the st
- Arbain, Dayar,Sargent, Melvyn V.
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p. 1527 - 1536
(2007/10/02)
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