Study of a Conformational Equilibrium of Lisinopril by HPLC, NMR, and DFT

Table 1

Selected bond lengths (Å) and angles (deg) for the cis and trans isomer of lisinopril.

Parameter	s-cis	s-trans
Lengths
H56–O40	3.857	1.717
H56–O21	1.799	4.816
H23–O40	3.618	4.033
H56–N41	2.486	2.613
H56–N59	2.660	4.875
H23–N59	3.721	3.717
H23–N41	4.958	4.947
Bonds lengths
H56–O55	0.988	0.995
O55–C53	1.338	1.338
H23–O22	0.972	0.972
O22–C20	1.346	1.556
H43–H58	4.058	4.471
H48–H58	6.612	6.255
H49–H58	5.982	5.934
Energy (au)	−1359.2686	−1359.2729
Energy (Kcal/mol)	−852953.828	−852956.552
µ (Debye)	3.9300	10.6461
Bond angle
C53–O55–H56	112.8	103.1
C18–C20–O21	125.0	124.8
N41–C39–O40	120.5	121.2
O54–C53–O56	121.6	122.2
Dihedral angle
H23–O22–C23–O24	172.5	174.2
O40–C39–C41–C50	2.3	176.6
O54–C53–O55–C53	−158.2	178.1
O40–H56–O55–C53	7.7	−41.8
O21–H56–O55–C53	156.8	3.9
Charge
O40	−0.49	−0.53
H56	+0.47	+0.45
O55	−0.60	−0.50
H23	+0.42	+0.42
O22	−0.55	−0.56