Synthesis of β-1,2-linked triarabinosylated PSY1 started from the generation of the arabinose donor (Scheme 1a) and the 4-hydroxyproline acceptor (Scheme 1b). For the synthesis of the arabinose donor we converted L-arabinose 5 into its corresponding furanoside by Fischer glycosylation, which then underwent a thioglycosylation to form ethyl thioarabinofuranoside 6. Simultaneous protection of the 3-, and 5-OH of furanoside 6 with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane (TIPDS) was achieved, after which the 2-OH was protected using freshly prepared p-methoxybenzyl (PMB) bromide, to form intermediate 7. We found that reported procedures that used commercially available PMB bromide were ineffective. However, using freshly prepared PMB bromide (see ESI) for installation of the PMB moiety at C2-O was successful (52% yield). Lastly, the TIPDS protecting group was removed and replaced with benzyl groups by treatment of 7 with tetrabutylammonium fluoride followed by benzylation using benzylbromide and NaH to obtain arabinose donor 8. In this step, both L-α (8) and L-β (S4) arabinofuranoside were obtained (ratio 3.25:1; determined by 1 H NMR analysis of both isolated compounds, Figure ). Specifically, L-α-arabinofuranoside 8 was identified by a doublet of the anomeric proton at 5.31 ppm with a J-coupling constant of 2.38 Hz, whereas the anomeric proton of L-β arabinofuranoside S4 was found at 5.35 ppm with a J-coupling constant of 4.94 Hz. Formation of both anomers most probably originated from a yet not understood furanose-ring mutarotation process in which the thioethyl group inverts. Importantly, both enantiomers led to the same 1,2-cis-linked product when applied in the next step (vide infra).