Table 1.

Temperature coefficients of amide protons in the azetidine-containing dipeptide derivatives 4, 7, 10

Compd	R1, R2	Δδ/ΔT (ppb/K)
		α-NHa	CONHa,b
(S,S)-4a	H, C(CH)3	−2.5	−3.5
(R,S)-4a	H, C(CH)3	−2.0	−4.0
(S,S)-4b	H, CH2Ph	−2.5	−4.5
(R,S)-4b	H, CH2Ph	−1.6	−2.9
(S,S)-4c	H, CH2CH(CH3)2	−3.5	−4.0
(S,S)-4d	H, Chx	−3.0	−4.0
(R,S)-4d	H, Chx	−2.5	−5.5
(S,S)-4e	CH3, CH3	−2.5	—
(R,S)-4e	CH3, CH3	−2.5	—
Compd	R3
(S,R)-7a	CH3	−3.3	−5.1
(R,R)-7a	CH3	−2.4	−4.1, −5.4
(S,S)-7b	CH2Ph	−3.6	−4.5
(R,S)-7b	CH2Ph	−2.2	−5.3
(S,S)-7c	CH(CH3)2	−2.5	−8.1
(R,S)-7c	CH(CH3)2	−1.8	−4.8, −5.2
(S,S)-7d	CH2CH(CH3)2	−3.5	−5.6
(R,S)-7d	CH2CH(CH3)2	−2.2	−4.6
Compd	R4
(S,S)-10a	Fmoc	−2.8	−4.7
(S,S)-10b	CO2CH2C6H4Cl	−3.0	−4.3, −5.5
(S,S)-10c	CO2CH2C6H4NO2	−3.0	−4.7, −5.1
(S,S)-10d	CO2Ph	−2.1	−4.0
(S,S)-10e	CO2C10H7	−3.1	−4.5
(S,S)-10f	SO2C10H7	−4.0	−4.6, −5.7
(S,S)-10g	CO2(CH2)2Ph	−2.7	−4.9, −5.6
(S,S)-10h	CONHCH2Ph	−4.0	−4.8
(S,S)-10i	CONHCH(Me)Ph	−3.8	−4.7

^aDetermined by least-squares linear regression analysis from measurements over the range 30–60 °C (seven points), in DMSO-d₆.

^bCONH₂ for series B and C.