Table 3.

Summary of computational results on calculations on acetylated methyl esters of 4S-fluoroproline (flp) and 4R-fluoroproline (Flp).^a

				O…C=O			Erel,
molecule	amide	pucker	quadrant	d, Å	ϕ, °	ψ, °	kcal mol−1
Ac-flp-OMe	trans	endo	αP/δ	3.19	−75	−3	0.4
	trans	endo	PPII/β	3.10	−72	173	0.0
	cis	endo	αP/δ		−80	6	0.6
	cis	endo	PPII/β		−78	−175	0.2
	trans	exo	αP/δ	2.79	−54	−37	2.1
	trans	exo	PPII/β	2.78	−57	144	1.9
	cis	exo	αP/δ		−59	−34	3.7
	cis	exo	PPII/β		−61	158	3.3
Ac-Flp-OMe	trans	exo	αP/δ	2.79	−54	−38	0.2
	trans	exo	PPII/β	2.78	−56	142	0.0
	cis	exo	αP/δ		−58	−35	1.6
	cis	exo	PPII/β		−60	157	1.4
	trans	endo	αP/δ	2.89	-60	-34	2.4
	trans	endo	PPII/β	2.93	−65	153	1.9
	cis	endo	αP/δ		−72	−21	3.5
	cis	endo	PPII/β		−75	167	2.9

^aCalculations were conducted at the DFT level of theory with the M06–2X method and the 6–311++G(3d,3p) basis set in implicit water. All structures are the result of geometry optimizations with the given combination of amide conformation (trans or cis), ring pucker (exo or endo), and quadrant of the Ramachandran plot (α-helix(α_R)/δ conformation or PPII/extended(β) conformation). All energies are relative to the lowest energy conformation of the indicated diastereomer. All conformations within 0.6 kcal mol^–1 of the lowest energy conformation are indicated in color.