This ought to work:
^\d+\s?(\([^\)]+\)\s?)?Z$
Haven't tested it though, but let me give you the breakdown, so if there are any bugs left they should be pretty straightforward to find:
First the beginning:
^ = beginning of string
\d+ = one or more decimal characters
\s? = one optional whitespace
Then this part:
(\([^\)]+\)\s?)?
Is actually:
(.............)?
Which makes the following contents optional, only if it exists fully
\([^\)]+\)\s?
\( = an opening bracket
[^\)]+ = a series of at least one character that is not a closing bracket
\) = followed by a closing bracket
\s? = followed by one optional whitespace
And the end is made up of
Z$
Where
Z = your constant string
$ = the end of the string