use warnings;
$sentence='kinase inhibitor SET6 activates p16(INK4A) in cell-wall.';
my @phrases = ('kinase i', 'inhibitor', 'tor SET6', 'SET6', 'p16(INK4A)', 'cell');
my $phrases_re = join '|', map { quotemeta } @phrases;
$sentence =~ s/(^| )($phrases_re)(?= |$)/$1#$2#/g;
print $sentence, "\n";