sentence: Attempts toward a usable semisynthetic vaccine , described below , concern six out of nine GBS STs.Since 2016 , several synthetic methods for the oligosaccharide repeating units of GBS CPS were published : [ 1 ] a dimer of the branched polysaccharide from ST Ia [ 53 ] ; ( 2 ) regioselective routes to building blocks that accessed the ST Ia and Ib repeating units [ 58 ] ; ( 3 ) the synthesis of three different pentasaccharide frameshifts of ST III [ 54 ] that were later investigated as a decasaccharide fragment composed of two repeating units to reveal the portion necessary for antibody recognition [ 56 ] ; ( 4 ) a branched heptasaccharide of the repeating unit of ST II [ 59 ] ; ( 5 ) ST V [ 60 ] ; and ( 6 ) a hexasaccharide repeating unit with the dimer of this repeating unit from ST VII [ 61 ] .