Efficient continuous flow synthesis of ethyl shikimate: the first step in the synthesis of Tamiflu

Continuous flow asymmetric synthesis of chiral active pharmaceutical ingredients and their advanced intermediates

Catalytic enantioselective transformations provide well-established and direct access to stereogenic synthons that are broadly distributed among active pharmaceutical ingredients (APIs). These reactions have been demonstrated to benefit considerably from the merits of continuous processing and microreactor technology. Over the past few years, continuous flow enantioselective catalysis has grown into a mature field and has found diverse applications in asymmetric synthesis of pharmaceutically active substances. The present review therefore surveys flow chemistry-based approaches for the synthesis of chiral APIs and their advanced stereogenic intermediates, covering the utilization of biocatalysis, organometallic catalysis and metal-free organocatalysis to introduce asymmetry in continuously operated systems. Single-step processes, interrupted multistep flow syntheses, combined batch/flow processes and uninterrupted one-flow syntheses are discussed herein.

Continuous-Flow Synthesis of (–)-Oseltamivir Phosphate (Tamiflu)

Herein the anti-influenza drug (–)-oseltamivir phosphate is prepared in continuous flow from ethyl shikimate with 54% overall yield over nine steps and total residence time of 3.5 min from the individual steps. Although the procedure involved intermediate isolation, the dangerous azide chemistry and intermediates involved were elegantly handled in situ. It is the first continuous-flow process for (–)-oseltamivir phosphate involving azide chemistry and (–)-shikimic acid as precursor.

Evolution of flow-oriented design strategies in the continuous preparation of pharmaceuticals

This review focuses on the flow-oriented design (FOD) in the multi-step continuous-flow synthesis of active pharmaceutical ingredients.

Safe and highly efficient adaptation of potentially explosive azide chemistry involved in the synthesis of Tamiflu using continuous-flow technology

Tamiflu is one of the most effective anti-influenza drugs, which is currently manufactured by Hoffmann-La Roche from shikimic acid. Owing to its importance, more than 60 synthetic routes have been developed to date, however, most of the synthetic routes utilise the potentially hazardous azide chemistry making them not green, thus not amenable to easy scale up. Consequently, this study exclusively demonstrated safe and efficient handling of potentially explosive azide chemistry involved in a proposed Tamiflu route by taking advantage of the continuous-flow technology. The azide intermediates were safely synthesised in full conversions and >89% isolated yields.