Bowman–Birk inhibitor analogues containing 2, 3 and 4-carbon analogues of the natural disulfide were synthesised via solid phase microwave-assisted RCM and found to have K_i values against chymotrypsin in the low to sub-micromolar range, the best replacement for the disulfide arising from the linkage by RCM of two L-homoallylglycine residues.