Pyridyl esters of .alpha.-substituted amino acids

A compound of the formula:

• ##STR5## wherein, R is oxygen, sulfur, methylene or carbonyl;
• R' is fluoro, bromo, chloro, trifluoromethyl, methyl, methoxy or methylthio;
• p is zero, one or two;
• W is oxygen or sulfur;
• t is zero, one, two, three or four;
• Y is independently selected from hydrogen, lower alkyl, lower haloalkyl, lower alkoxy, lower alkylthio, lower alkylcarbonyl, lower alkoxycarbonyl, lower acyloxy, halogen, cyano, nitro, and lower haloalkylthio;
• and Z is independently selected from the values of Y, cycloalkyl having 3 to 8 carbon atoms, and lower haloalkoxy;
• or Y and Z form a methylenedioxy group;
• R.sup.2 is hydrogen or lower alkyl;
• R.sup.3 is lower alkyl of 2 to 5 carbon atoms, lower alkenyl of 2 to 5 carbon atoms, lower haloalkyl of 1 to 4 carbon atoms, lower haloalkenyl of 2 to 4 carbon atoms, or lower cycloalkyl of 3 or 4 carbon atoms;
• R.sup.4 is hydrogen or fluoro;
• R.sup.5 is hydrogen, cyano, ethynyl, methyl, ethyl or trifluoromethyl;
• and the salt thereof of a strong inorganic acid or organic acid.