$re = '/(\p{L}+)\b(?![\p{P}\p{S}])/m';
$str = 'Bajos
Ascensor
habs.:3';
$subst = "\1:";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php