Indole-3-propionic acid, structure

Structural information on aromatic donor molecule binding was obtained initially by using H NMR relaxation measurements to give distances from the heme iron atom to protons of the bound molecule. For example, indole-3-propionic acid, a structural homologue of the plant hormone indole-3-acetic acid, was found to bind approximately 9-10 A from the heme iron atom and at a particular angle to the heme plane (234). The disadvantage of this method is that the orientation with respect to the polypeptide chain cannot be defined. Other donor molecules examined include 4-methylphenol (p-cresol) (235), 3-hydroxyphenol (resorcinol), 2-methoxy-4-methylphenol and benzhydroxamic acid (236), methyl 2-pyridyl sulfide and methylp-tolyl sulfide (237), and L-tyrosine and D-tyrosine (238). Distance constraints of between 8.4 and 12.0 A have been reported (235-238). Aromatic donor proton to heme iron distances of 6 A reported earlier for aminotriazole and 3-hydroxyphenol (resorcinol) are too short because of an inappropriate estimate of the molecular correlation time (239), a parameter required for the calculations. Distance information for a series of aromatic phenols and amines bound to Mn(III)-substituted HRP C has been published (240). 

In agreement with the derived structure hexahydrodeazanorvobasine, upon oxidation with chromic acid, formed a-methylbutyric acid in addition to acetic and propionic acids. Also in complete harmony with the chosen structure was the formation of trideuterio-16-epivobasine by a base-catalyzed deuteration (MeOD/MeONa) of vobasine followed by reprotonation of the indole nitrogen. 

It is perhaps because of the fact that an asymmetric structure, leading to optical activity, apparently is not a prerequisite for growth substance activity, that the early work of Kogl and Verkaaik ona-indole-3-propionic acid... 

XLIII) the IR-spectrum of its iodide is also similar to that of sempervirine iodide and further shows the absence of a vinyl group. Catalytic hydrogenation of melinonine G over Adams catalyst in aqueous alkaline solution gives an indole which yields propionic and acetic acids on modified Kuhn-Roth oxidation and which, therefore, contains a C-ethyl group. All this evidence is accommodated in structure XLIV for melinonine G the indolic reduction product must then have structure... 

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