2-Deoxy-2,3-didehydro-D-N--acetylneuraminic acid 24967-27-9 6-((2R)-1,2,3-Trihydroxypropyl)(4S,5R,6R)-5-(acetylamino)-4-hydroxy-5,6-dihydro-4H-pyran-2-carboxylic acid AIDS-114183 AIDS114183 DANA Neu5Ac2en