português para inglês Medicina Medicina: farmacêutica Organic Chemical Formula

I am translating a text from a patent in Portuguese, for a pharmaceutical product. The patent contains many chemical formulas (organic) and the following formula contains the word "en", and I am not sure if it means "N" (nitrogen) or something else that I am not familiar with.

Does anyone know how this word should be translated in the formula?

Here is the formula:

(2R,3S) 3-terc-butoxicarbonilamino-2-hidroxi-3-fenilpropionato de 4-acetoxi-2-α-benzoiloxi-5β-20-epoxi-l,7-β-10-β-tri-hidroxi-9-oxo-tax-ll--13α-ila (I) (brackets added)

Here is the context sentence:

A presente invenção refere-se a um processo para a preparação de PFA's, mais especificamente, derivados da classe de taxóides, especialmente (2R,3S) 3-terc-butoxicarbonilamino-2-hidroxi-3-fenilpropionato de 4-acetoxi-2-α-benzoiloxi-5β-20-epoxi-l,7-β-10-β-tri-hidroxi-9-oxo-tax-ll-en-13α-ila (I) e (2R,3S) 3-benzoilamino-2-hidroxi-3-fenilpropionato de 4-acetoxi-2-α-benzoiloxi-5β-20-epoxi-1,7β-10-β-tri-hidroxi-9-oxo-tax-ll-en-13α-ila (II).

Thank you very much in advance.

Laura