UDP-ACETYL-CARBOXYVINYL-GLUCOSAMINE UDP-GlcNAc-pyruvate enol ether UDP-N-acetyl-3-(1-carboxyvinyl)-D-glucosamine UDP-N-acetyl-3-O-(1-carboxyvinyl)-D-glucosamine UDP-N-acetylglucosamine-3-O-pyruvate ether