The present invention provides compounds of formula (I),

##STR00001##

wherein: R.sub.1 is unsubstituted C.sub.1-C.sub.6 alkyl; L.sub.a is substituted or unsubstituted C.sub.1-C.sub.6 alkyl linker, substituted or unsubstituted C.sub.3-C.sub.10 carbocycle, substituted or unsubstituted heterocycle comprising one or two 5- or 6-member rings and 1-4 heteroatoms selected from N, O and S, or substituted or unsubstituted heteroaryl comprising one or two 5- or 6-member rings and 1-4 heteroatoms selected from N, O and S; and R.sub.2 and R.sub.3 are each, independently, H, substituted or unsubstituted C.sub.1-C.sub.6 alkyl, or substituted or unsubstituted C.sub.6-C.sub.10 aryl; or alternatively, R.sub.2 and R.sub.3, together with the nitrogen atom to which they are attached, form a substituted or unsubstituted heteroaryl comprising one or two 5- or 6-member rings and 1-4 heteroatoms selected from N, O and S or a substituted or unsubstituted heterocycle comprising one or two 5- or 6-member rings and 1-4 heteroatoms selected from N, O and S.

The invention also provides pharmaceutical compositions and methods for treating neurological diseases, such as multiple sclerosis.