Catalyst‐Free and Metal‐Free Approach towards Synthesis of Amide‐ and Thioamide‐Linked β‐Carboline‐Pyridine Conjugates and Estimation of Their Photophysical Properties

Abstract

A series of novel β‐carboline‐pyridine conjugates linked though amide and thioamide tethers were synthesized under catalyst‐free and metal‐free conditions using β‐carboline alkaloid; Kumujian C as a template. The tert‐butyl hydroperoxide (TBHP)‐mediated reaction with 2‐aminopyridines provided the amide linked β‐carboline‐pyridine conjugates whereas the Willgerodt‐Kindler reaction in presence of elemental sulfur furnished thioamide tethered analogues. The alkyl, aryl, as well as heteroarylamines underwent Willgerodt‐Kindler reaction with Kumujian C to afford diverse β‐carboline linked thioamides. Both the protocols avoided the use of toxic metal catalysts and expensive additives to provide the products in moderate to excellent yields in a short duration. Interestingly, the amide linked β‐carboline‐pyridine conjugates displayed excellent photophysical properties with fluorescence quantum yields (ΦF) up to 38% rendering them as promising candidates for applications in biology and optoelectronic materials.

A modular and synthetic biosynthesis platform for de novo production of diverse halogenated tryptophan-derived molecules

“…McbB, one of the genes that drives the biosynthesis of marinacarbolines, was found in the organism Marinactinospora thermotolerans SCSIO 00652, and catalyzes a Pictet-Spengler cyclization process 76 . Beta-carbolines in general have been shown to have very interesting chemical characteristics including optoelectronic properties, potential as anti-cancer agents, and many other bioactivities [77][78][79][80] . Specifically, the molecules formed through the Mcb pathway in Marinactinospora thermotolerans have been shown to have antimalarial, cytotoxic, and anti-inflammatory activities 81,82 .…”

An efficient metal-free and catalyst-free C–S/C–O bond-formation strategy: synthesis of pyrazole-conjugated thioamides and amides

“…Although, these protocols are useful and have exhibited wide applications in organic synthesis ( Figure 2 ), the scope of these reported methods may suffer from drawbacks such as harsh reaction conditions, use of expensive reagents, prolonged reaction times, low product yields, and cumbersome product isolation procedures [ 58 – 62 ]. In the recent past, our group also reported two methods towards the exploration of elemental sulfur for the formation of a sulfur-containing framework; however, these methods suffer from some drawbacks such as lack of diversity in starting substrate, need of base/catalyst and limitation of starting reagents [ 63 – 64 ]. Our current work was completed with the exploration of the position of the pyrazole ring like C-3, C-4 and C-5 and we also employed the pyrazole-based AXB3s (4-iodo-C-3 and 4-iodo-C-5).…”