Synthesis of Oseltamivir-Tamiflu

Oseltamivir, sold under the brand name Tamiflu, is a widely used antiviral drug for the treatment and prevention of influenza. It belongs to a class of compounds known as neuraminidase inhibitors, which block the viral enzyme responsible for the release of new virus particles from infected cells.

The mechanism of action involves inhibition of the neuraminidase enzyme on the surface of the influenza virus, preventing viral propagation in the host. The molecule mimics the transition state of enzymatic cleavage, accounting for its high binding affinity. Structurally, oseltamivir features a highly functionalized cyclohexene core bearing amine, ester, and ether functional groups, along with multiple stereogenic centers critical for biological activity.

In this practice problem, we focus on the synthesis of oseltamivir, which involves several highly controlled transformations with defined stereochemistry. These include the formation and regioselective ring opening of epoxides, lactone formation, hydrolysis, and strategic functional group manipulations.

The synthesis begins from (-)-Quinic acid, a naturally occurring cyclohexane polyol with multiple hydroxyl groups and well-defined stereochemistry. This starting material provides a convenient chiral scaffold exploited to construct the target molecule with the required configuration at each stereocenter.

As with all examples in this section, this discussion is presented solely for educational purposes and is not intended to represent a practical or real-world method of preparation.

Practice

Below is a simplified synthesis of Tamiflu starting from (-)-Quinic acid. Identify the missing reagents and intermediates, and suggest plausible mechanisms for the conversions 1-2 and 4-5.