Lys-CoA (1) is a selective inhibitor of p300 histone acetyltransferase (HAT) but shows poor pharmacokinetic properties because of its multiply charged phosphates. In an effort to overcome this limitation, truncated derivatives of 1 were designed, synthesized and tested as p300HAT inhibitors as well as substrates for the CoA biosynthetic bifunctional enzyme phosphopantetheine adenylyltransferase-dephospho-CoA kinase (PPAT/DPCK). Lys-pantetheine (3) and Lys-phosphopantetheine (2) showed no detectable p300HAT inhibition whereas 3′-dephospho-Lys-CoA (5) was a modest p300 inhibitor with IC₅₀ of 1.6 μM (compared to IC₅₀ of ∼50 nM for 1 blocking p300). Compound 2 was shown to be an efficient substrate for PPAT whereas 5 was a very poor DPCK substrate. Further analysis with 3′-dephospho-Me-SCoA (7) indicated that DPCK shows relatively narrow capacity to accept substrates with sulfur substitution. While these results suggest that truncated derivatives of 1 will be of limited value as lead agents for p300 blockade in vivo, they augur well for prodrug versions of CoA analogues that do not require 3′-phosphate substitution for efficient binding to their targets, such as the GCN-5 related N-acetyltransferases.