import re
text = 'This is an sample string which have some information in brackets (info; matchingString, someotherString).'
regex= r"\([^()]*?matchingString[^)]*\)"
print( re.findall(regex, text) )
aW1wb3J0IHJlCnRleHQgPSAnVGhpcyBpcyBhbiBzYW1wbGUgc3RyaW5nIHdoaWNoIGhhdmUgc29tZSBpbmZvcm1hdGlvbiBpbiBicmFja2V0cyAoaW5mbzsgbWF0Y2hpbmdTdHJpbmcsIHNvbWVvdGhlclN0cmluZykuJwpyZWdleD0gciJcKFteKCldKj9tYXRjaGluZ1N0cmluZ1teKV0qXCkiCnByaW50KCByZS5maW5kYWxsKHJlZ2V4LCB0ZXh0KSAp