SELECT DISTINCT REGEXP_SUBSTR(strain.name, '[(]([^()]*|[(][^()]*[)])+[)]$', 1, 1) AS name
FROM (
  SELECT strain.id, TRIM(SUBSTR(strain.name, 1, INSTR(strain.name, '[')-1)) AS name
  FROM species_strain strain
) strain
WHERE INSTR(strain.name, '(', 1, 1) > 0