Not using a regex, but a simple automaton: 
#!/usr/bin/perl
use warnings;
use strict;

use Test::More;

sub groups {
    my $string = shift;
    my $depth  = 0;
    my @return = (q());
    for my $char (split //, $string) {
        $depth++ if '(' eq $char;
        $depth-- if ')' eq $char;
        if ((2 > $depth and qw/) (/[$depth] eq $char)
                or (' ' eq $char and ! $depth)) {
            push @return, q();
        } else {
            $return[-1] .= $char;
        }
    }
    s/^ *| *$//g for @return; # trim
    return [ grep length, @return];
}


is_deeply(groups("A (B C D)"),
                ["A", "B C D"]);
is_deeply(groups("A (B C D) (E F G)"),
                ["A", "B C D", "E F G"]);
is_deeply(groups("A B (C (D E) (F G)) (H I)"),
                ["A", "B", "C (D E) (F G)", "H I"]);
is_deeply(groups("A B (C (D E) (F G)) X Y (H I)"),
                ["A", "B", "C (D E) (F G)", "X", "Y", "H I"]);


done_testing();

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لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: Help modifying recursive regex by choroba
in thread Help modifying recursive regex by beeflobill

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