Pappalardo, Giovanni published the artcileIndoles. III. Ultraviolet spectra of methoxyindoles and of methoxyindole-2-carboxylic acids and esters, HPLC of Formula: 20538-12-9, the publication is Gazzetta Chimica Italiana (1958), 574-90, database is CAplus.
The ultraviolet spectra of indole (I), 3-, 4-, 5-, 6-, 7-methoxyindoles (II-VI), indole-2-carboxylic acid (VII), 1-, 3-, 4-, 5-, 6-, 7-methoxyindole-2-carboxylic acids (VIII-XIII), VII Et ester (XIV), VIII Me ester (XV), Et 3-, 4-, 5-, 6-, and 7-methoxyindole-2-carboxylates (XVI-XX) were measured in alc. and C6H6, and λmaximum in A. (log ε) were tabulated. II-VI were also measured in 0.05N HCl and 0.05N NaOH. N-Hydroxyindole-2-carboxylic acid (prepared by Na-Hg reduction of ο-O2NC6H4CH2COCO2H) methylated with MeI and NaOMe and the product (40%) crystallized (Et2O-petr. ether) gave VIII, m. 186-7° (dilute Me2CO), identical with the acid obtained by saponification of XV. XVI saponified in aqueous alkali and the product extracted with Et2O gave IX, m. 147° (50% MeOH), unstable to exposure to air. Na2S2O5 (2.8 g.) added portionwise to 5 g. 4,2,6-H2N(O2N)2C6H2Me (XXI) in 25 ml. HNO3 (d. 1.52) at 0°, kept 30 min., the solution poured into 50 ml. alc. at 0° containing 0.3 g. CuO, the mixture heated on a steam bath, steam-distilled to remove the 2,6-(O2N)2C6H3Me (XXII) formed, and the distillate extracted with Et2O yielded 46% XXII. XXI (4 g.) in 70 ml. concentrated HCl at 0° diazotized with saturated aqueous NaNO2 (1.5 g.), kept 30 min., treated with 20 ml. 50% H3PO2 previously cooled to -5, stirred 1 hr. at 0°, kept 24 hrs. at 0° and the diluted solution steam-distilled yielded 43% XXII. XXII reduced to 2,6-O2N(H2N)C6H3Me converted to 2,6-O2N(MeO)C6H3Me, transformed to 2,6-O2N-(MeO)C6H3CH2COCO2H and reduced with Fe(OH)2 yielded 65% X, m. 235.5-36° (decomposition). Saponification of XVIII gave a quant. yield of XI, m. 199.5-200°. Reduction of 2,4-O2N(MeO)C6H3CH2COCO2H and purification of the product (70%) by repeated precipitation from Et2O with petr. ether gave crystalline XII, m. 196-7° (alc.). Similarly by the method of Reissert (C.A. 17, 3186) 2,3-O2N(MeO)C6H3CH2COCO2H was converted to 65% XIII, m. 181.5-82° (dilute alc.). Esterification of VIII by refluxing in absolute alc. containing 15% dry HCl gave the corresponding Et ester as an unstable oil, and accordingly VIII was similarly esterified in MeOH to 75% XV, m. 67-8° (ligroine). XIV with Me2SO4 and NaOH yielded 90% XVI, m. 92-3° (ligroine). X esterified with alc. HCl yielded 83% XVII, m. 171.5-2.5° (dilute alc.). Absolute alc. (100 ml.) containing 1.5 ml. concentrated H2SO4 refluxed 10 hrs. with 10 g. 4-MeOC6H4NHN:CMeCO2H [m. 139.5° (C6H6)] and the product (20%) crystallized (dilute alc.) gave XVIII, m. 156-6.5°. Esterification of XII with alc. HCl gave 83% ester, crystallized (dilute alc.) to give XIX, m. 135-6°. Similar esterification of XIII yielded 80% XX, m. 113.5-14.5° (after recovery by steam distillation), also produced by cyclization of 2-MeOC6H4NHN:CMeCO2Et (m. 88.5-89°) with AcOH-H2SO4. Cyclization with dry HCl gave an unidentified indolic compound, m. 168°. IX (5 g.) and 0.7 g. Cu chromite heated at 200-10° in 30 ml. anhydrous quinoline, the cooled mixture poured onto cracked ice and HCl, extracted with Et2O, the washed and dried extract evaporated, and the residue distilled at 115-17°/5 mm. and recrystallized (petr. ether) gave II, m. 69.5°; 1,3,5-(O2N)3(C6H3) addition compound, m. 171-2° (Et2O). X similarly decarboxylated, extracted with Et2O, and the product (58%) fractionally crystallized (petr. ether) gave III, m. 69.5-70.5°; picrate, m. 159-60° (C6H6). Similarly decarboxylation of XI, XII, and XIII and extraction of the products with Et2O yielded 70, 40, and 80%, resp. IV, b2 124-5°, m. 55.5-56° (petr. ether-EtOH) (picrate, m. 143-3.5°); V, 142-4°, m. 92.5° (petr. ether-EtOH)(picrate, m. 132°); and VI, b6 122° [picrate, m. 154-5° (decomposition)]. The introduction of the MeO group more or less distinctly altered the spectral behavior of the indole nucleus owing to the inductive effect of the substituent which, in some instances, was superimposed on the weak mesomeric effects of the indole and indolenine chromophores. The spectral characteristics of the methoxyindole-2-carboxylic acids and esters were related to those of the chromophore-NH(C:C)nC of pyrrole-2-carboxylic acid with maximum spectral influence when the substituent MeO group was canonically located.
Gazzetta Chimica Italiana published new progress about 20538-12-9. 20538-12-9 belongs to indole-building-block, auxiliary class Indole,Ester,Ether, name is Ethyl 7-methoxy-1H-indole-2-carboxylate, and the molecular formula is C12H13NO3, HPLC of Formula: 20538-12-9.
Referemce:
https://www.nature.com/articles/s41429-020-0333-2,
Preparation of Indole Containing Building Blocks for the Regiospecific Construction of Indole Appended Pyrazoles and Pyrroles