Total Synthesis of Ellipticine Quinones, Olivacine, and Calothrixin B

Abstract

A direct route to the synthesis of biologically active ellipticine quinones, olivacine, and calothrixin B is described. The prominent key steps involved are Friedel-Crafts hydroxyalkylation followed by oxidation and directed ortho-lithiation reactions of readily available indole-2-carboxylate esters with appropriately substituted pyridine and quinoline carboxaldehydes.

Concise Total Syntheses of Pyr­ido[4,3‐b]carbazole Alkaloids Using Copper‐Mediated 6π‐Electrocyclization

“…A 20‐fold excess of MnO 2 and prolonged reaction time (7 d) sufficed for the oxidation of 34 at room temperature, affording 36 in 72 % yield from 15 . Removal of the N‐ Boc group in 36 with BBr 3 at –78 °C provided olivacine ( 6 ) in 60 % yield; the NMR spectroscopic data of this synthetic material were in good agreement with those of natural 6 16a. On the other hand, 3,4‐dihydroolivacine ( 7 ) was generated by treatment of 35 with BBr 3 at –78 °C.…”

“…The solvent was removed, and the residue was separated on TLC plate (aluminum oxide 60 F 254 basic, Merck) with hexane/AcOEt (2:1) to give 6 (20 mg, 60 %) as colorless crystals, m.p. > 300 °C (ref 16a. > 300 °C).…”

Total Syntheses of Carbazole Alkaloids Lansine F and Clauemarazole D

“…The combined organic extracts were washed with brine (10 mL), then dried over sodium sulfate, filtered, and concentrated in vacuo. Ellipticine quinone (6): [8] Ceric ammonium nitrate (530 mg, 0.97 mmol) was added to as olution of 3 (40 mg, 0.16 mmol) in THF/H 2 O ( 1:1, 8mL). The mixture was stirred at 0 8Cf or 0.5 h, and then extracted with ethyl acetate (6 mL 2).…”

“…The residue was purified by chromatography on silica gel (22 %e thyl acetate in petroleum ether) to afford the ellipticine quinone 6 (26 mg, 65 %) as ar ed solid:m p > 300 8C[ lit. [8] mp ( 10:1, 8mL). The resulting mixture was heated at 100 8Cf or 12 ha nd cooled.…”

Total synthesis of calothrixins A and B via oxidative radical reaction of cyclohexenone with aminophenanthridinedione

“…4-9 The first total synthesis of calothrixins was reported by Kelly, using an o -lithiation strategy. 10 Several other syntheses of calothrixins have also been reported exploring different synthetic strategies such as metallations, 11 hetero Diels-Alder, 12 Friedel-Crafts acylation reaction, 11a, 13 etc. A few other syntheses of calothrixins have also been reported.…”