A short synthesis of aromatic analogs of the aranotins

Abstract

Various pyrazino[ 1,2-~:4,5'-a']diindoles have been synthesized corresponding in structure t o the diketopiperazine type dimers o f indole-and indoline-2-carboxylic acids. 7,14-Dihydroxy-6H,13H-pyrazino[l,2-a:4,5-~']diindole-6,13-dione reacted w i t h sulfur monochloride and pyridine t o give epidithio and epitrithio derivatives. These are aromatic analogues o f the aranotins. T h e structure o f the epitrithio derivative was verified by single-crystal x-ray crystallography. T h e space group is P?,P21Pz, w i t h pertinent cell data as follows: a = 9.199 (4), b = 13.846 (4), c = 13.248 (3) A, and 2 = 4.

(Cyanovinyl)ketenes From Azafulvenones. An Apparent Retro-Wolff Rearrangement

“…Formation of nitriles 22 and 23 can be due to the trapping of a rearranged ketene intermediate ( 27 ) (Scheme ). Dimer 21 was characterized by NMR, MS, and X-ray crystallography (Figure ).

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5 ORTEP drawing of diindolo[1,2- a :1‘,2‘- d ]pyrazine-8,16-dione ( 21 ) (30% probability level).

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Products from dehydration of dicarboxylic acids derived from anthranilic acid

“…It was identified as the diacetylated compound 18 by parallel synthesis from compound 19 (by heating in Ac 2 O). This fused diketopiperazine indole dimer can be prepared in two steps from the diacid 17b, 23 which intriguingly is the chainchain tautomer of the alleged compound 17a. Compound 19 can also be prepared by high temperature treatment of the methyl ester of indoxylic acid.…”

“…For analytical purposes this material could be recrystallised from EtOH to yield a white solid, mp 282-284 ЊC (dec.) (lit. 23 Compound 21 (0.26 g, 0.50 mmol) was hydrolysed with NaOH (0.20 g) in 10 mL dioxane-1.5 mL water at reflux for 16 h. The mixture containing the red dianion of the product was poured into 30 mL 2 M HCl, after which time the yellow coloured product could be filtered off. After drying, this gave 0.15 g (94%) of compound 19, mp 394 ЊC (lit.…”

“…After drying, this gave 0.15 g (94%) of compound 19, mp 394 ЊC (lit. 23 Compound 20 (0.63 g, 2.0 mmol) was stirred with 3.0 mL TFAA in 15 mL MeCN at 50 ЊC for 1 h. The reaction mixture was poured on 50 mL water, after which the product was filtered off and washed with water. This gave 0.67 g (66%) yellow powder, mp 385 ЊC (dec.); IR ν max /cm Ϫ1 : 1813, 1707, 1596, 1575, 1453, 1398, 1366, 1338, 1242, 1175, 1098, 755; When left standing in air, the compound was hydrolysed to compound 19, and the performed elemental analysis also match this compound (Found C, 68.10; H, 3.21; N, 8.72%).…”