Synthesis of novel sialidase inhibitors to target influenza A virus and Chagas’ disease

Abstract

This thesis is divided into two parts. Part One describes inhibitors towards influenza neuraminidase and Part Two describes inhibitors towards Trypanosoma cruzi trans-sialidase.

In Part One, a description of the influenza virus is given followed by details of the current approved therapies and our approach.

Influenza is a virus that has the ability to cause a pandemic with a possible high mortality rate. The life cycle of the influenza virus exhibits several key stages that, if inhibited, would hinder its replication and have potential as therapeutic targets. The two currently approved drugs on the market (zanamivir (25) and oseltamivir (6)) target influenza neuraminidase. Influenza neuraminidase has the function of cleaving terminal sialic acid groups from glycoconjugates present at the surface of cells, enabling the release of the newly formed viral particles.

Our strategy towards the syntheses of novel inhibitors against influenza neuraminidase is based on 2,3-difluorosialic acid (19). Modifications were made at position C-5 of sialic acid to replace the 5-N-acetamido with a 5-N trifluoroacetamido group. The formation of 5-N-trifluoroacetamido-2,3-difluorosialic acid (41) was achieved by deprotecting 5-N-acetamido-2,3-difluorosialic acid (52) using methanesulfonic acid. Modifications were also performed at position C-7, introducing a series of 7-N-alkylamines on 2,3-difluorosialic acid (47) by oxidative cleavage of the glycerol side chain and reductive amination.

A series of 4-epi-N-alkylamines were introduced onto the Neu5Ac2ene moiety, with the intention of probing the size of the enzyme pocket available in the surroundings of position C-4.

The C-4, C-5 and C-7 modified compounds were tested against a panel of influenza viruses (CSIRO). Furthermore, 7-N,N-diethylamino-2,3-difluorosialic acid (39) was tested against influenza neuraminidase N9. The compounds showed poor levels of inhibition, with the IC50’s referring to the influenza neuraminidase N9 wild type, being 326 and 68 mM for the 7-N-ethyl-N-methylamino (37) and 7-N,N diethylamino-2,3-difluorosialic acid (39), respectively.

(See figure in full thesis)

In Part Two, a description of Chagas’ disease is given followed by the currently approved therapies and our approach.

Chagas’ disease is endemic in Central and South America and is caused by a parasite, Trypanosoma cruzi. There are currently two approved drugs to treat Chagas’s disease, and both have a similar mode of action, inducing oxidative stress in the parasite.

Our approach is to target Trypanosoma cruzi trans-sialidase (TcTS), which has two important roles in the life cycle of the parasite. TcTS cleaves sialic acid from glycoconjugates present at the host cell surface and transfers them to mucin like receptors present on the parasite. This action allows the parasite to evade the host defence mechanisms. In addition, TcTS enables the parasite to enter the host cell during the infection process.

Our strategy towards the synthesis of novel inhibitors against Trypanosoma cruzi trans-sialidase is based on 2,3-difluorosialic acid (19), akin to the inhibitors developed in Part One. Several modifications were made at position C-7 via cleavage of the glycerol side chain and introducing a series of cyclic 7-N-alkylamines by reductive amination.

(See figure in full thesis)

The synthesised compounds were then tested against trypomastigotes, the infectious form of the parasite. The inhibitory results showed an IC50 of 3.1 mM for 7-N pyrrolidino-2,3-difluorosialic acid (145); 35.5 mM for 7-N-morpholino-2,3 difluorosialic acid (146); and 4.2 mM for 7-N-anilino-2,3-difluorosialic acid (147).

Date of Award	1 Sept 2010
Original language	English
Awarding Institution	University of Bath
Supervisor	Andrew Watts (Supervisor) & Barry Potter (Supervisor)