methoxymethyl (2R,3R,4S)-3-acetamido-4-(2,3-bis(tert-butoxycarbonyl)guanidino)-2-((5S,6R)-6-(methoxymethoxy)-2,4,8,10-tetraoxaundecan-5-yl)-3,4-dihydro-2H-pyran-6-carboxylate