Syntax for matches and does not equal on charge account

Summary

What is the syntax for operations on the charge account.

Content

I am having trouble making approval rules work.

We have a charge account such as 201.12345.50001.000.00000.00000 where the segment2 is the natural account and segment 3 is the cost centre.

I have one rule: Charge Account Matches (.*)\\.(.*)\\.[5-6][0-9][0-9][0-9][0-9]\\.(.*)\\.(.*)\\.(.*)\\.(.*), where I am trying to isolate accounts where the segment 3 is in the 50000 or 60000 series.  It seems to work.

But I also need the "anti-condition" and am doing

Charge Account Does not Equal (.*)\\.(.*)\\.[5-6][0-9][0-9][0-9][0-9]\\.(.*)\\.(.*)\\.(.*)\\.(.*)

This condition does not work.

I am building similar rules for both Requisition and PO approvals and would appreciate some help.