Dimethyl fumarate

Dimethyl fumarate is the methyl ester of fumaric acid.

Reactions
Dimethyl fumarate is an ester and an α,β-unsaturated electrophilic compound, undergoing reactions typical to them. It is also a diene acceptor in the ordinary Diels-Alder reaction, where the reactivity of its vinylidenic bond is enhanced by the two electron-withdrawing ester groups. Due to the geometry of the starting ester, the Diels-Alder product will have a trans configuration.

Uses
Dimethyl fumarate is used to treat psoriasis. It is a lipophilic, highly mobile molecule in human tissue. However, as an α,β-unsaturated ester, dimethyl fumarate reacts rapidly with the detoxifying agent glutathione by Michael addition. When administered orally, it does not survive long enough to be absorbed into blood.

Another use for dimethyl fumarate is mold inhibition, mostly for leather products. But see below for the problems this has caused.

Tests in mouse models have been conducted with the aim of using it as part of a specific cancer treatment.

Dimethyl fumarate has been shown to provide benefit in a mouse model of multiple sclerosis and phase III clinical trials in patients are in progress under the name BG-12. It has shown good results with relapsing-remitting multiple sclerosis.

Risks
Dimethyl fumarate has been found to be an allergic sensitizer at very low concentrations, producing extensive, pronounced eczema that is difficult to treat. Concentrations as low as 1 ppm may produce allergic reactions. There are only a handful of equally potent sensitizers.

The extreme sensitizing risk was brought to public attention by the "poison chair" incident, where Chinese manufacturer Linkwise produced two-seater sofas with dimethyl fumarate sachets inside to inhibit mould while they were in storage or transport. In Finland where the chairs were sold from 2006–2007, sixty users were given serious rashes. The cause was identified as dimethyl fumarate-induced allergic reaction by Tapio Rantanen, M.D. from Finland, and his original article became the cover story in the July issue of British Journal of Dermatology. In the United Kingdom, sofas sold by Argos, Land of Leather and Walmsley Furnishing containing the chemical caused over a hundred injuries. Argos withdrew the sofas from stores and contacted buyers to collect those that had been sold — with Land of Leather withdrawing the sofas without notifying buyers and Walmsley saying they had removed the sachets from sofas they sold after the danger came to light. Complaints have been made that dates on the sofas were altered and sofas containing the sachets sold. Land of Leather and Walmsley are facing a ₤10 million class action suit over their reaction to the incident, joining the manufacturer in denying the sofas are connected to their customers injuries. The danger came to public attention when the BBC Watchdog program alerted consumers to the sofas.

In the European Union the use of dimethyl fumarate for consumer products has been forbidden since 1998, and since January 2009 the import of products containing dimethyl fumarate is also forbidden.

The EU Commission Decision 2009/251 of 17 March 2009 requiring Member States to ensure that products containing the biocide dimethylfumarate are not placed or made available on the market has definitely forbidden any marketing of products containing dimethyl fumarate into the European Union. The ban on dimethyl fumarate as laid down in Decision 2009/251 establishes a maximum concentration of dimethyl fumarate in products of 0.1 ppm. Products containing more than 0.1 ppm dimethyl fumarate shall be withdrawn from the market and recalled by consumers as of 1 May 2009.