I share some confusion about what you want, but perhaps this a closer approximation to it: 

c:\@Work\Perl>perl -wMstrict -le
"my %xlate_map = qw/ ( l_paren  ) r_paren  { l_curly  } r_curly /;
 my $xlate_targets = join '', map quotemeta, keys %xlate_map;
 ;;
 sub xlate {
   my ($s, $targets, $hr_map) = @_;
   ;;
   (my $t = $s) =~ s{ ([$targets]) }{$hr_map->{$1}}xmsg;
   return $t;
   }
 ;;
 my $str = 'a { b } c ( d ) e';
 my $xlt = xlate($str, $xlate_targets, \%xlate_map);
 print qq{'$xlt'};
"
'a l_curly b r_curly c l_paren d r_paren e'

[download]

Update 1: This can be generalized (and slowed down) a bit, and also, if you have Perl version 5.14+, simplified (and perhaps un-slowed) a bit (note use of  /r regex modifier in  s///r substitution): 

c:\@Work\Perl>perl -wMstrict -le
"use 5.014;
 ;;
 my %xlate_map = qw/ ( l_paren  ) r_paren  { l_curly  } r_curly /;
 ;;
 sub xlate {
   my ($s, $hr_map) = @_;
   ;;
   my $targets = join '', map quotemeta, keys %$hr_map;
   return $s =~ s{ ([$targets]) }{$hr_map->{$1}}xmsgr;
   }
 ;;
 my $str = 'a { b } c ( d ) e {{F}} ((G))';
 my $xlt = xlate($str, \%xlate_map);
 print qq{'$xlt'};
"
'a l_curly b r_curly c l_paren d r_paren e l_curlyl_curlyFr_curlyr_cur
+ly l_parenl_parenGr_parenr_paren'

[download]

Update 2: Another approach: complete encapsulation; works with any version; perhaps a bit faster (note  /o regex modifier in  s///o substitution): 

c:\@Work\Perl>perl -wMstrict -le
"print qq{Perl version $] };
 ;;
 BEGIN {
   my %xlate_map = qw/ ( l_paren  ) r_paren  { l_curly  } r_curly /;
   my $xlate_targets = join '', map quotemeta, keys %xlate_map;
   ;;
   sub xlate {
     my ($s) = @_;
     ;;
     (my $t = $s) =~ s{ ([$xlate_targets]) }{$xlate_map{$1}}xmsog;
     return $t;
     }
   }
 ;;
    my $str = 'a { b } c ( d ) e {{F}} ((G))';
    my $xlt = xlate($str);
    print qq{'$xlt'};
"
Perl version 5.008009
'a l_curly b r_curly c l_paren d r_paren e l_curlyl_curlyFr_curlyr_cur
+ly l_parenl_parenGr_parenr_paren'

[download]

Any of these approaches can be further simplified to operate directly upon  $_ if that's what you really need.

In reply to Re: Regex - Is there any way to control when the contents of a variable are interpolated? (Using "$1" and '$1' in regex replacements) by AnomalousMonk
in thread Regex - Is there any way to control when the contents of a variable are interpolated? (Using "$1" and '$1' in regex replacements) by JDoolin

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