Cassanic acid

These conditions do not obtain in cassanic acid (p. 728) although this acid dehydrogenates to 1 7 8-trimethylphenanthrene. 

Ketohydroxycassanic acid, C20H32O4, has also been used for another mode of degradation by Ruzicka, Dalma and Scott (1941). On oxidation by chromic acid in acetic acid it yields diketocassanic acid, C20H30O4, m.p. 225°, [a]u ° — 44° (EtOH), which forms a methyl ester, m.p. 108°, (EtOH), and is reduced by sodium amyloxide at 220° to cassanic acid, C20H34O2, m.p. 224°, [a]f - - 3° (CHCI3), which on selenium dehydrogenation also yields 1 7 8-trimethylphenanthrene. 

Ruzicka, Engel, Ronco and Berse have shown that the carboxyl group in cassanic acid is not at position by replacing this carboxyl group by isopropyl, dehydrogenating the product with selenium to a hydrocarbon, which proved not to be identical with a s)mthetic... 

The hydroxyl in cassaic acid is secondary because oxidation of the acid with chromic acid generates a diketo acid (m.p. 238-239°, [a] —164.5° in ethanol) which did not give positive reactions for aldehydes and which formed a methyl ester (m.p. 129-130°), a dioxime (m.p. 130-132°), and a disemicarbazone (m.p. 290°). Ruzicka and Dalma (19) have suggested that the saturated acid, free of oxygen-containing substituents, from which cassaic acid is derived, be named cassanic acid. The diketo acid obtainable... 

In conclusion, it may be pointed out that a number of structural formulas have been suggested for cassanic acid, but they are speculative except for the phenanthrene nucleus. 

Cassaine, the alkaloid available in greatest quantity, has been the one most studied chemically. Cassaine, C24H39O4N, on mild acid hydrolysis yields -dimethylaminoethanol and cassaic acid, C20H30O4 (/). This acid has been shown to possess a double bond, which is in a position a,j3 to the carboxyl group (A ,ax 215 mfx, e 20,000), a hydroxyl, and a ketonic function (1, 2). The recent chemical interest in this Erythrophleum alkaloid has been focused on the structural elucidation and synthesis of cassaic acid. Compounds related to this acid have been named (d) as derivatives of cassanic acid, C20H34O2, which can be obtained from cassaic acid by reduction of the double bond, oxidation to a diketone, followed by Wolff-Kishner reduction. 

Cassaidine, C24H41O4N 4), on acid hydrolysis also provides j8-di-methylaminoethanol and the acid, cassaidic acid, C20H32O4. Adihydroxy-cassanic acid and a diketocassanic acid can be obtained from cassaidic acid which are identical with samples prepared from cassaic acid. Thus the relationship between cassaic acid and cassaidic acid (consequently cassaine and cassaidine) is that the keto group in the former is found as a hydroxy function in the latter. 

The information available at this point does not provide evidence for the methyl group at C-10 and one of those at C-4. The carbon skeleton in cassanic acid was established by the transformation of vouacapenic acid (III) to compound IV and ultimate conversion to cassanic acid... 

Further independent evidence for the structure of cassanic acid was provided by the synthetic work discussed in the next section. 

Kai-ho-chien," 775 Kcstodihydromethylmorphimethine, 235 l-Keto-6 7-dimethoxy-2-methyI-tetialn droisoquiiioline, 354 KetolqrihDOi cassanic acid, 728, 729, 730 Ketohydroigrcassenic add. See Cassaic acid, 728... 

Cassanes.— -Caesalpin (41), from Caesalpinia pulcherrima, possesses the cassane skeleton, and is thus related to the bitter principles isolated from the seeds of Caesalpinia bonducella. Cassminic acid is a minor constituent of the bark of Erythrophleum guineense. Spectroscopic measurements and an interrelationship with cassane-16,19-dioic acid have established " it as 6-oxo-7-hydroxycass-13-ene-16,19-dioic acid. N.m.r. measurements and bromination-dehydrobromina-tion studies are in accord with the axial 14a-configuration now accepted for the cassamic acid diterpenes. 

Cassane and Miscellaneous Tricyclic Diterpenoids.—A group of furanoid diterpenoids, related to the caesalpins, has been isolated from Pterodon emargina-and P. pubescens. They include compounds (39—42). Some further diterpene alkaloids of the cassaic acid class have been isolated from Erythro-phleum ivorense. 

Cassane is the basic skeleton of cassaic acid, the parent diterpenoid of alkaloids from the bark of Erythrophleum guinese and other Erythrophleum species (Fa-baceae). These act as local anaesthetics, cardiotonics, antihypertonics, and also induce cardiac arrest. Erythrophleum alkaloids such as cassaidine, cassain and cassamine are 2-(iV,iV-dimethylamino)ethyl esters of cassaic acid derivatives. 

Johnston, J. P., and K. H. Overton The Pimarane Cassane Rearrangement. Synthesis of a Potential Intermediate from Isopimaric Acid. J. Chem. Soc. Perkin I 1973, 853. 

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