I am attempting to replace all of the `&`'s in a string with `&amp` unless the `&` is followed by `lt`, `apos`, `gt` or `quot`.

Running this statement

```
select 
    regexp_replace('&lt &apos &gt &quot &','&(^lt|^gt|^quot|^apos)','&amp')

```

however results in no changes to the string. 

The output I would be looking for is 

```
'&lt &apos &gt &quot &amp'

```