Just a thought that below should work.
Field-symbols : <mat_val> type matnr,
<f_val> TYPE ANY.
constants : lv_mat type char5 value 'MATNR'.
ASSIGN lv_val to <f_val>.
ASSIGN COMPONENT <f_val> OF STRUCTURE <l_fs_name> TO <mat_val>.
and now <mat_val> should have value 44.
But this is used when your variable name is dynamic like MATNR1, MATNR2 and you have decide variable at run time. But try once.