Table 5. Calculations for Intermediates in Reaction Network of Figure 2 for the Case of Phe-I and d-Ribose.

	energy (kcal/mol) for (X,X′)
conformer	(S,R)	(S,S)	(R,R)	(R,S)
most stable ADD	1.2	0.1	0.7	0
most stable CYC	–6.0	–7.0	–8.4	–7.8
free energy barrier for cyclization of deprotonated ADD to CYC	3.9	3.2	3.9	1.1