KXW kxw (2~{S})-4-[[(2~{R},3~{S},4~{R},5~{R})-5-(6-aminopurin-9-yl)-3,4-bis(oxidanyl)oxolan-2-yl]methyl-[3-(pyridin-2-ylamino)propyl]amino]-2-azanyl-butanoic acid KXW