BN isosteres of indole

Abstract

Indole is a heterocycle of great importance to biological systems and materials applications. Synthesis of indole and its derivatives has been a major focus of research for over a century. BN/CC isosterism is an emerging strategy for expanding the structural diversity of indole-based compounds. Two classes of BN indoles have been reported to date: the well-studied “external” BN indoles (or 1,3,2-benzodiazaborolines), and the recently reported “fused” BN indoles. This perspective presents the history of both classes of indole isosteres, with a general overview of their synthesis, functionalization, and properties.

Zirconocene-Based Methods for the Preparation of BN-Indenes: Application to the Synthesis of 1,5-Dibora-4a,8a-diaza-1,2,3,5,6,7-hexaaryl-4,8-dimethyl-s-indacenes

“…[27][28][29][30][31] There has therefore been a significant amount of activity in this field since its resurgence in the mid 2000's. [32][33][34][35][36][37][38] A corollary of the interest in these molecules is the need for new synthetic routes to such species that are efficient, modular and scalable. 35 While much progress has been made, new methodologies are still of interest for preparing these materials and accessing BN frameworks for which current methods are not suited.…”

Divergent reactivity of nucleophilic 1-bora-7a-azaindenide anions

“…This reversibility enabled us to probe the relative affinity of 2a and 2b for binding CO2 (Scheme 4). When freshly isolated 6a or 6b was dissolved in THF with one equivalent of 2b or 2a, respectively, the equilibrium established over the course of a few hours indicated that the CO2 adduct 6b is strongly favoured over 6a; Keq at 298 K was measured by 1 H NMR spectroscopy to be 54 (5). ‖ This is in keeping with the notion that methyl substituted 2b is a more electron rich anion that acts as a stronger nucleophile to RX or CO2 electrophiles.…”

“…The synthesis and evaluation of BN isosteres of archetypical aromatic hydrocarbons has been a fruitful and active area of research in main group and organic materials chemistry in the past decade. [1][2][3][4][5][6] The substitution of a C=C double bond with the more polarized B=N unit within a larger aromatic framework can have beneficial effects on the packing, 7, 8 absorption 9,10 and electron transporting 11,12 properties of the molecules and materials compared to the all carbon frameworks. 13 As such, there has also been significant interest in defining the differences between all carbon and BN compounds at a more fundamental level in the most basic building units of polycyclic aromatic hydrocarbons (PAHs).…”

Synthesis and characterization of an unnatural boron and nitrogen-containing tryptophan analogue and its incorporation into proteins

“…The addition of a BN-analogue of tryptophan to the UAA toolbox could offer an alternative approach to probing protein function and fluorescent properties while also demonstrating the utility of azaborine chemistry in a biological context. It has been shown that the p K a of the N–H proton in the internal BN-indole is higher than that of the natural indole (∼30 and 21, respectively) and has altered spectroscopic characteristics 23,24. These distinctive properties encouraged us to pursue the synthesis and application of a BN-analogue of tryptophan.…”