Isolation and synthesis of cryptosanguinolentine (isocryptolepine), a naturally-occurring bioactive indoloquinoline alkaloid

Abstract

The isolation and properties of the heterocycle are detailed and the diversity of chemical approaches toward the natural product are systematically ordered and reviewed.

Indole Editing Enabled by HFIP‐Mediated Ring‐Switch Reactions of 3‐Amino‐2‐Hydroxyindolines

“…Next, we extended our transformation for the synthesis of indolo [3,2-c]quinolines (Scheme 6b). [14][15] The compound 2 aa-2 la upon treatment with the Vilsmeier-Haack reagent underwent successive cyclization/oxidation/detosylation sequences and gave indolo [3,2-c]quinolines 5 aa-5 la in good yields. [8a] Completion of total synthesis of isocryptolepine [14] was also accomplished by a facile deprotection of the benzyl group [16] of 5 ae and methylation.…”

DABCO‐Promoted Selective Photochemical C−N Coupling: Access to Unsymmetrical Azahelicenes

“…However, compared to classical phenanthridine derivatives, they have been studied very little due to the lack of convenient methods for their synthesis, although it is known that incorporation of an additional heterocyclic moiety can significantly improve both the biological activity and photophysical properties. [3,4] Due to the high demand for these compounds, several modular strategies have been developed to date, including thermal and photochemical methods for constructing the middle pyridine ring. [1a,5] A special place among them is occupied by a synthesis strategy based on the generation and intramolecular cyclization of the iminyl radical due to homolytic cleavage of the NÀ O bond and formation of a new CÀ N bond in orthofunctionalized biaryl compounds.…”

Metal‐Free Rapid Diastereoselective Construction of Isocryptolepine Core via Elecrophilic Dearomatization ‐ Inramolecular Michael Addition Sequence

“…Since the first laboratory preparation in 1950 over 25 general methods of indolo[3,2-c]quinoline synthesis were described. [16][17][18] Diversity of approaches to the construction of isocryptolepine and its analogues includes such reactions as Graebe-Ullmann reaction, [19] Suzuki coupling, [20] cyanate and nitrene cyclizations, [21] photochemical reactions, [22] Buchwald-Hartwig intramolecular arylation, [23] decarboxylative Heck cyclization, [24] Pd-catalyzed CÀ N and CÀ C bond formation, [25] Pictet-Spengler reaction, [26] electrocyclization reactions, [27] Fischer indolization, [28] intramolecular Wittig reaction, [29] furan to indole recyclization conjugated with Michael addition, [30] Curtius rearrangement, [31] aza-[4 + 2]-cycloaddition, [32] radical Beckmann rearrangement, [33] Vilsmeier reaction with triazine. [34] Previously we have reported one-pot, metal-free protocol for preparation of poly annulated hetrocyclic compounds bearing 4-azaquinoline core.…”