(3'r,4's,5s,5's,6'r)-3',4',5'-Tris-benzyloxy-6'-benzyloxymethyl-3-[(4-ethylphenyl)methyl]-3',4',5',6'-tetrahydro-spiro[furo[3,4,f]benzoisoxazole-5(7h),2'-[2h]pyran]