正则表达式查找不属于超链接的文本

I'm trying to find a single regular expression that I can use to parse a block of HTML to find some specific text, but only if that text is not part of an existing hyperlink. I want to turn the non-links into links, which is easy, but identifying the non-linked ones with a single expression seems more troublesome. In the following example:I'm trying to find a single regular expression