# Functionalized in Triplicate: A Ring‐By‐Ring Approach to Tailored Prodiginine Derivatives for Site‐Specific Conjugation Through Click Chemistry

## TL;DR

This paper introduces a new chemical method to modify a toxic compound called prodigiosin so it can be selectively attached to other molecules, improving its potential for targeted drug delivery.

## Contribution

The novelty is enabling site-specific conjugation of prodigiosin via functionalizing each of its three pyrrole rings using click chemistry.

## Key findings

- Azides and maleimides were successfully installed on each pyrrole ring of prodigiosin for functionalization.
- The methodology allows for protein-conjugable prodiginines through CuAAC, SPAAC, and thiol-maleimide reactions.
- The synthetic routes yield 3.2–4.7% over 12–15 steps, providing valuable tools for expanding click chemistry applications.

## Abstract

The tripyrrole prototype alkaloid prodigiosin and members of the prodigiosin family are structurally diverse bacterial secondary metabolites. The privileged scaffold accounts for versatile biological activities, for example, antimicrobial, antitumoral, and immunosuppressive. Its Lewis‐basic lipophilic tripyrrole core and the aliphatic side chains allow for passive membrane diffusion, thereby trespassing the natural permeability barrier. However, diffusion‐controlled uptake is accompanied by low target specificity, hampering the development of tailored prodigiosin therapeutics and their selective delivery to target sites. To address this downside, this work focuses on providing the chemical methodology to synthesize prodiginines that are amenable to click chemistry on each of the three pyrrole moieties and facilitate the development of prodigiosin conjugates. Installing reactive azides and maleimides in the A‐, B‐, and C‐ring of the cytotoxic scaffold enables further functionalization per azide‐alkyne cycloaddition (CuAAC and SPAAC) and thiol‐maleimide addition, giving rise to protein‐conjugable prodiginines for the first time. The presented synthetic routes comprise yields of 3.24.7% over 1215 steps and grant access to valuable synthetic elements for expanding the toolbox of click chemistry to other pyrrole‐, pyrrolidinone‐, and tetramic acid‐containing natural products. Together, the devised methodology for prodiginine derivatization will collectively advance the development of alkaloid‐based conjugate therapeutics, eligible for target‐selective delivery.

Prodigiosin is a potent cytotoxic alkaloid but lacks target selectivity. We advance functionalization of all three pyrrole rings of prodigiosin to enable site‐specific conjugation via click chemistry. The presented azide‐ and maleimide‐functionalized prodiginines are suitable for generating covalent prodiginine conjugates and attaching auspicious vectors for targeted drug delivery. The developed methodology promotes the expansion of conjugable pyrrole‐based building blocks and natural products in the future.