import re
regex = r"\([0-9]\)\s+([^.!?]+[.!?])"
test_str = "(1) This is my first sentence, it has to be captured. This is my second sentence."
print(re.findall(regex, test_str))
aW1wb3J0IHJlCgpyZWdleCA9IHIiXChbMC05XVwpXHMrKFteLiE/XStbLiE/XSkiCnRlc3Rfc3RyID0gIigxKSBUaGlzIGlzIG15IGZpcnN0IHNlbnRlbmNlLCBpdCBoYXMgdG8gYmUgY2FwdHVyZWQuIFRoaXMgaXMgbXkgc2Vjb25kIHNlbnRlbmNlLiIKCnByaW50KHJlLmZpbmRhbGwocmVnZXgsIHRlc3Rfc3RyKSk=