# Isolation, Identification, and Total Synthesis of Pyranoquinolinone Alkaloids from Conchocarpus mastigophorus Kallunki (Rutaceae)

## TL;DR

This study isolates and synthesizes new pyranoquinolinone alkaloids from a Rutaceae plant, revealing their stereochemistry and synthetic methods.

## Contribution

The paper introduces new pyranoquinolinone alkaloids and their stereocontrolled synthesis using asymmetric dihydroxylation and epoxidation.

## Key findings

- Four pyranoquinolinone alkaloids were isolated, including three new compounds.
- The absolute configurations of the new compounds were determined using synthetic comparisons.
- A stereocontrolled synthesis method was developed for two new compounds with high yields and diastereoselectivity.

## Abstract

In this study, the phytochemical profile of Conchocarpus
mastigophorus was investigated, leading to the isolation
of four pyranoquinolinone alkaloids, including huajiaosimuline (1) and three new compounds: 3′-acetoxy-4′-hydroxyzanthosimuline
(2), epoxyzanthosimuline (3), and mastigophorine
(4). All new compounds possess two chiral centers and
exist as a 1:1 mixture of epimers, differing in the configuration
of a chiral center at the pyran ring. The absolute configurations
of the epimers 2 and 3 were determined by
data comparison with identical synthetic compounds, revealing mixtures
of (2S,3'R)- and
(2R,3'R)-configured epimers
in both
cases. By employing Sharpless asymmetric dihydroxylation and Shi epoxidation
as key stereoselective steps, stereocontrol at C3 was achieved in
the synthesis of compounds 2 and 3, respectively.
Our synthesis approach provided 3'R- and 3'S-configured 2 in three steps (41–46%
overall yield, 95% dr) and 3'R-configured 3 in 2 steps (61% overall yield, 90% dr) from 4-hydroxy-1-methyl-2­(1H)-quinolinone and citral.