With the goal of upgrading the diversity of chemical space, in this manuscript, we explored the possibility of late-stage reshaping of pre-discovered "natural" peptides into high-value monocyclic and bicyclic structures using synthetic linchpin. We developed the versatile C2symmetric linchpin KYL with an aldehyde and two thiol-reactive groups, which makes it possible to produce monocyclic and bicyclic structures as well macrocycles that bear exogenous pharmacophores. Though C3v symmetric cross-linkers have been ubiquitously applied in phage- and mRNA-displayed libraries, their high symmetry makes it difficult to further expand the diversity (e.g., introduce exogenous pharmacophores). Pharmacophores can be trivially introduced into lower symmetry C2 linchpins, allowing the possibility to combine cyclization and modification. However, C2 linchpins are problematic in forming bicycles: Heinis and coworkers employed C2 linchpin to cross-link 4 cysteine residues in phage displayed peptides to yield bicyclic peptides, but the challenge in such approach is controlling regioselectivity. In contrast, C2-symmetric KYL and analogous linchpins, which act on cysteine side chains and N-terminus, give rise to single regioisomer of bicycles.