Conformationally Constrained Analogues of Diacylglycerol. 18. The Incorporation of a Hydroxamate Moiety into Diacylglycerol-Lactones Reduces Lipophilicity and Helps Discriminate between sn-1 and sn-2 Binding Modes to Protein Kinase C (PK-C). Implications for Isozyme Specificity.