as well as its geometrical isomers, its optically active forms as enantiomers,

(I)

R¹ is CH₂—CH₂-phenyl, CH₂—CH₂-napthyl, CH₂-phenyl, or CH₂-napthyl;

R^2a and R^2b are each independently are H or (C¹-C¹²)alkyl;

Cy is a phenyl substituted by (1), (2) or (3):

(1) an oxadiazole group;

(2) 1 or 2 moieties selected from the group consisting of —NH—CO—R³, —SO₂—NR³R^3′ and —CO—NR³R^3′ wherein R³ and R^3′ are independently selected from H and (C₁-C₁₅)alkyl; or

(3) B-R⁴ wherein B is an ethynyl group and R⁴ is a (C₁-C₁₂)alkyl phenyl;

(II)

R^2a and R^2b are each H, R¹ is —CH₂-A with A being phenyl optionally substituted by cyano, halogen, methoxy, hydroxyl, phenoxy, —NO₂, or trifluoromethyl, and Cy is phenyl or biphenyl substituted by —SO₂R³, or —CO—NR³R^3′ where R^3′ is H and R³ is (C₇-C₁₂)alkyl or (C₇-C₁₅)alkyl; or

(III)

R^2a and R^2b are each H, R¹ is selected from the group consisting of phenyl, benzyl, phenethyl, or 1-methylbenzyl which may be substituted by (C₁-C₆)alkyl or cycloalkyl, and Cy is phenyl or biphenyl substituted by —SO₂R³, or —CO—NR³R³ where R³ is (C₇-C_{1 5})alkyl.