dereference :      Heap, Object α → α,    // Rückverweis auf Wert

documentclass{article}
%usepackage[cp437]{inputenc}%%% if you do this, store your file in the DOS encoding
usepackage[utf8]{inputenc}
usepackage[x11names]{xcolor}
usepackage{listings}
newcommand*{RightComment}[1]{hfillmakebox[4.0cm][l]{emph{color{green}#1}}}
begin{document}
% begin{lstlisting}[emph={Object,α,Heap},emphstyle={color{blue}sffamily},emph={[2]dereference},emphstyle={[2]color{red}sffamily},mathescape=true,escapechar=&,columns=flexible,extendedchars=true]
%   dereference :      Heap, Object α → α,  &RightComment{Rückverweis auf Wert}&
% end{lstlisting}
newcommand{emphalpha}{$color{blue}alpha$}
begin{lstlisting}[emph={Object,$alpha$,Heap},emphstyle={color{blue}sffamily},emph={[2]dereference},emphstyle={[2]color{red}sffamily},mathescape=true,escapechar=&,columns=flexible,extendedchars=false]
   dereference :      Heap, Object &emphalpha& $to$ &emphalpha&    &RightComment{Rückverweis auf Wert}&
end{lstlisting}
end{document}