Ring-constrained amino acid surrogates of formula I: where R1, R2, R3, R4, R5, R6a, R6b, R7, and y are as defined in the specification, methods for synthesizing ring-constrained amino acid surrogates of formula I, methods of use of ring-constrained amino acid surrogates of formula I, including use in linear or cyclic compounds which include a plurality of amino acid residues and one or more ring-constrained amino acid surrogates of formula I and linear or cyclic compounds which include a plurality of amino acid residues and one or more ring-constrained amino acid surrogates of formula I.