Monomethyl auristatin E intermediate-12;N-benzyl-1,1-dimethoxy-N,3-dimethylpentan-2-amine;(2S,3S)-N-benzyl-1,1-dimethoxy-N,3-dimethylpentan-2-amine;(2S,3S)-N-Bbenzyl-1,1-dimethoxy-N,3-dimethylpentan-2-amine;Benzenemethanamine, N-[(1S,2S)-1-(dimethoxymethyl)-2-methylbutyl]-N-methyl-