Код:
$text = preg_replace('/(?<=[^a-zA-Z0-9а-яА-Я]|^)[a-zA-Z0-9а-яА-Я]{1,3}(?=[^a-zA-Z0-9а-яА-Я]|$)/u', '', $text);
$text = str_replace(' ', ' ', preg_replace('/[^a-zA-Z0-9а-яА-Я\s,]+/u', ' ', $text));
$text = preg_replace('/(?<=[\s,]|^)([a-zA-Z0-9а-яА-Я]+)(?=[\s,]|$)/u', '<a href="#">$1</a>', $text);