The MySQL docs state that: MySQL uses Henry Spencer's implementation of regular expressions, which is aimed at conformance with POSIX 1003.2. MySQL uses the extended version to support pattern-matching operations performed with the REGEXP operator in SQL statements. Ok, so we're talking about POSIX ERE. This page lists the details...
Anyway, regcomp uses POSIX BRE or ERE, which doesn't support look-ahead or look-behind. .+{(.+)} Grab the string you want from group index 1. DEMO...