Preg_replace error

[eluser]Unknown[/eluser]
A PHP Error was encountered
Severity: Warning
Message: preg_replace() [function.preg-replace]: Unknown modifier '('
Filename: helpers/custom_helper.php
Line Number: 20

Code:

$text = preg_replace('([[:space:]()[{}])(www.[-a-zA-Z0-9@:%_\+.~#?&//=]+)',
'<a href="http://\\\\2" class="oembed" target="_blank">\\2</a>', $text); #line 20

Disregard the other \\