What is the difference between a linker and a spacer?
A spacer primarily controls distance and flexibility, while a linker may also provide a reactive group, cleavage mechanism, self-immolative function, or connection between two molecular components. The terms overlap in common usage.
How should I choose PEG length?
Use the shortest PEG that provides adequate accessibility and solubility. Longer PEG can increase flexibility, hydrodynamic size, analytical complexity, and purification difficulty.
Can several linkers be combined in one peptide?
Yes, when attachment sites and chemistries are orthogonal. Reaction order, protecting groups, payload stability, purification, and analytical confirmation must be planned together.
Are all listed modifications suitable for on-resin installation?
No. Many reactive, bulky, light-sensitive, or unstable groups are better introduced after cleavage. The library identifies a typical route, but sequence-specific review is required.
Which linker is best for intracellular release?
The answer depends on the target compartment and mechanism. Disulfides respond to reducing environments; Val-Cit/PABC systems are associated with lysosomal proteases; hydrazones and acetals respond to acidic conditions.
How are crosslinked peptides characterized?
LC-MS and analytical HPLC are commonly used for identity and purity. Complex conjugates may require orthogonal chromatography, UV/fluorescence analysis, amino acid analysis, or application-specific testing.
Can you recommend an alternative when direct conjugation is difficult?
Yes. Feasibility review may identify a more suitable attachment site, spacer, bioorthogonal handle, heterobifunctional linker, or staged conjugation route.
Can linkers be used with cyclic or stapled peptides?
Often yes, provided the linker attachment does not compete with the closure chemistry or disrupt the constrained pharmacophore. Reaction order is especially important.
What information is needed for a feasibility review?
Provide the sequence, modification position, conjugation partner, linker preference, desired release mechanism, quantity, purity, formulation, and intended application.
How do I choose between a flexible spacer and a rigid linker?
Flexible spacers such as PEG or aminohexanoic acid can improve accessibility and reduce steric hindrance, while more rigid linkers can preserve a defined distance or orientation. The best choice depends on the target, attachment geometry, and desired biological or analytical behavior.