Synthesis of Bromoindole Alkaloids from Laurencia brongniartii

Abstract

A regioselective synthesis of N-carbomethoxy-2,3,5-tribromoindole (6) via a sequential one-pot bromination-aromatization-bromination of N-carbomethoxyindoline (2) is described. The process for the transformation of 2 into 6 permitted the isolation of stable reaction intermediates N-carbomethoxy-5-bromoindoline (3), N-carbomethoxy-5-bromoindole (4), and N-carbomethoxy-3,5-dibromoindole (5). Compound 6 was used to complete the total synthesis of the natural products 1b and 1c. In addition, bromination of N-carbomethoxyindole (11) afforded N-carbomethoxy-2,3,6-tribromoindole (13), from which the natural product 1a was synthesized.

Red Algae (Rhodophyta) from the Coast of Madagascar: Preliminary Bioactivity Studies and Isolation of Natural Products

“…The similarity of the 1 H and 13 C NMR spectra of 3 to those of 2 led us to assign compound 3 as 2,3,5,6-tetrabromoindole. Finally, the identity of compounds 1 – 3 was confirmed by the good agreement of their NMR data with those reported in the literature [7,8]. …”

“…153–154 °C [8]); UV (MeOH): λ (nm) = 234, 297, 305 (sh); fluorescence (MeOH): λ max (297 nm) = 317 nm; IR (ATR): ν (cm −1 ) = 3382, 2921, 1608, 1555, 1502, 1431, 1365, 1303, 1226, 1086, 995, 862; 1 H NMR (600 MHz, CDCl 3 ): δ (ppm) = 7.61 (s, 1 H, H-7), 7.77 (s, 1 H, H-4), 8.30 (br s, 1 H, NH); 13 C NMR and DEPT (150 MHz, CDCl 3 ): δ (ppm) = 93.75 (C-3), 112.15 (C-2), 115.39 (C-7), 116.69 (C-5), 119.00 (C-6), 123.18 (C-4), 128.22 (C-3a), 134.93 (C-7a); GC-MS (EI, 70 eV): m / z (%) = 437/435/433/431/429 (16/66/100/70/18, M + ), 356/354/352/350 (8/26/26/8), 275/273/271 (13/26/13), 216 (9), 194/192 (9/10), 167/165 (7/8), 136 (13), 112 (8), 86 (14); ESI-MS (−10 V): m / z = 428/430/432/434/436 [M − H] − ; Anal. calcd for C 8 H 3 Br 4 N: C 22.20, H 0.70, N 3.24; found: C 23.10, H 0.62, N 3.22%.…”

Synthesis of novel 2,8-disubstituted indolo[3,2-b]carbazoles

“…Because the latter corresponds to two indole nuclei connected via a methylene bridge, the reactivity of 2 should be similar to that of 2,3-disubstituted indoles and bromination of indoles is well described in literature. 14, 15 Hence, we explored a way to obtain ICZ 2 as the major reaction product in the initial condensation reaction. From our previous research it was apparent that elevated temperatures during the condensation favoured the oxidized ICZ 1.…”

Experimental thermochemical study of 5-bromoindole and 5-bromoindoline

“…These compounds have also attracted great attention in pharmacology, mainly because of their ability to develop antifungal and antibacterial agents, but also as candidates for anti-oxidant, direct oxidation/reduction of biomolecules, and other biological activities [1][2][3][4]. Due to their presence in water and soil as persistent organic pollutants, these organobromine compounds have also been the focus of considerable research work to determine their toxicity effects on the environment [4].…”