X is where Y is ???(CH2)m??? where m is an integer of 0 to 3, or Y is ???(CH2)n???Z???(CH2)p??? where n is an integer of 0 to 2, p is an integer of 0 to 2 and Z is a heteroatom (optionally substituted) or Z is a carbon atom substituted with one or two C1-6 alkyl groups;