Need help converting form 4 to 9

Stay away from regular expressions if you can at all help it. Using the switch statement with file globbing (-glob) or the starts_with/ends_with/contains operators can cover most of the cases where users use regular expressions. In your case you are just doing a straight string compare so regular expressions are way overkill.

Here's an example of your rule using the switch statement.

when HTTP_REQUEST {
  switch -glob [string tolower [HTTP::host]] {
    "demo.nature.com" {
      pool demo
    }
    "xml.nature.com" -
    "palgravexml.nature.com" {
      pool Autonomy
    }
    default {
      discard
    }
  }
}

-Joe