s/(\d+ *)L\-homoserine/${1}2\-Amino\-4\-hydroxybutyric\ acid/;

##</code><code>##

    s/(\d+ *)L-homoserine/${1}2-Amino-4-hydroxybutyric acid/;

##</code><code>##

    s/(\d*\s*)L-homoserine/${1}2-Amino-4-hydroxybutyric acid/;