The Nenitzescu Reaction in the Synthesis of New Abietane Diterpene Indoles
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Chemistry of Heterocyclic Compounds 2020, 56(10), 1366–1369
The Nenitzescu reaction in the synthesis of new abietane diterpene indoles Elena V. Tretyakova1*, Lyaisan R. Yarmukhametova2, Elena V. Salimova1, Olga S. Kukovinets2, Lyudmila V. Parfenova1 1
Institute of Petrochemistry and Catalysis, Ufa Federal Research Center of the Russian Academy of Sciences, 141 Oktyabrya Ave., Ufa 450075, Russia; e-mail: [email protected] 2 Bashkir State University, 32 Zaki Validi St., Ufa 450076, Russia Translated from Khimiya Geterotsiklicheskikh Soedinenii, 2020, 56(10), 1366–1369
Submitted February 5, 2020 Accepted after revisions June 10, 2020
The new abietane diterpene indoles were synthesized by the Nenitzescu reaction of 1a,4a-dehydroquinopimaric acid and its methyl ester with methyl-3-aminocrotonate. Keywords: abietane diterpenoids, indoles, quinopimaric acid, Nenitzescu reaction.
Compounds with the indole moiety are traditionally the subject of intensive study in the field of heterocyclic chemistry, which is owed to the unique biological properties and significant synthetic potential of this class of compounds.1 Indole is a part of the natural amino acid tryptophan and its metabolic products tryptamine and serotonin (5-hydroxytryptamine), which are biogenic amines, as well as indole-3-acetic acid (heteroauxin).2 In animals, serotonin functions as a neurotransmitter in central nervous system, and heteroauxin is a growth hormone in the plant kingdom and is used in agriculture to stimulate plant growth.3 Due to their physiological properties, indole derivatives are widely used in medical practice as effective drugs with various pharmacological activities (action on peripheral neurotransmitter processes, manifestation of hemorrhagic, sedative, and radioprotective properties).4 Examples of such compounds are the nonsteroidal anti-inflammatory agent indomethacin, β-adrenoceptor blocker pindolol, antidepressant dicarbine, and others.5 Several naturally occurring indoles are also clinically important. For example, mitomycins,6 ellipticine derivatives,7 and nortopsentines8 have high antitumor activity. The Nenitzescu indole synthesis is a convenient tool for the preparation of 5-hydroxyindole derivatives from β-enaminocarbonyl compounds and quinones.9 As a rule, 0009-3122/20/56(10)-1366©2020 Springer Science+Business Media, LLC
the direction of the reaction and the product yields depend on the structural features of the starting enamines or quinones, and benzo- and naphthoquinone derivatives were mainly used as quinones in this reaction.10 In this work, we chose 1а,4а-dehydroquinopimaric acid (3) and its methyl ester (4) as a novel quinone component that were not previously employed in the Nenitzescu reaction (Scheme 1). Diterpene quinone 3 is easily formed in two steps from quinopimaric acid (2), the diene adduct of levopimaric acid (1) and p-benzoquinone according to a published method.11 Methyl 3-aminocrotonate was used as the enamine component. Indole derivatives of 1а,4а-dehydroquinopimaric acid 5, 6 were synthesiz
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