1 6BM [(3s)-1-hydroxy-2-oxopiperidin-3-yl]phosphonic acid 1.000 2 4NG [(3s,5s)-1,5-dihydroxy-2-oxopyrrolidin-3-yl]phosphonic acid 0.714 3 KVM [(3s)-1-hydroxy-2,5-dioxopyrrolidin-3-yl]phosphonic acid 0.714