but are not limited to benzene 1 2 diyl benzene 1 3 diyl benzene 1 4 diyl naphthalene 1 8 diyl and the like the term u201c heteroarylene u201d refers to an arylene group comprising one or more heteroatoms selected from n s or o a u201c suitable protecting group u201d is a group which inhibits or suppresses undesirable chemical reactions but which is designed to be sufficiently reactive that it may be cleaved from the functional group in question under mild enough conditions that do not modify the rest of the molecule after deprotection the desired product is obtained protecting groups are well known to those skilled in the art and are suitably chosen from for amine groups boc where boc is tert butyloxycarbonyl fmoc where fmoc is fluorenylmethoxycarbonyl trifluoroacetyl allyloxycarbonyl dde i e 1 4 4 dimethyl 2 6 dioxocyclohexylidene ethyl or npys i e 3 nitro 2 pyridine sulfenyl and for carboxyl groups methyl ester tert butyl ester or benzyl ester for hydroxyl groups suitable protecting groups are methyl ethyl or tert butyl alkoxymethyl or alkoxyethyl benzyl acetyl benzoyl trityl trt or trialkylsilyl such as tetrabutyldimethylsilyl the use of further protecting groups are described in u2018 protective groups in organic synthesis u2019.