Fmoc-8-Amino-3,6-Dioxaoctanoic Acid (CAS 166108-71-0): Laying the foundation for future peptide therapies
Introduction:
Walk through any peptide synthesis laboratory ,and you will find shelves lined with small vials of white crystalline powders. Among them sits a compound that rarely makes headlines but quietly enables some of the most exciting advances in modern medicine.
That compound is Fmoc-8-amino-3,6-dioxaoctanoic acid, CAS 166108-71-0.At first glance, it does not look like much: a faintly yellow crystalline solid with a molecular weight of 385.41 g/mol.
But inside that modest molecule lies a combination of three functional features that make it indispensable: an Fmoc protecting group, a short PEG spacer, and a terminal carboxylic acid.
Together, these turn a simple building block into a precision tool for constructing complex biomolecules — from peptide nucleic acids (PNAs) to antibody-drug conjugates (ADCs) and beyond.
What Makes This Molecule Special: A Three-in-One Design
1. The Fmoc Group: A Reversible GatekeeperThe fluorenylmethoxycarbonyl (Fmoc) moiety is the gold standard for temporary amine protection in solid-phase peptide synthesis (SPPS).
It is robust during coupling steps, yet cleaves cleanly under mild basic conditions (typically 20% piperidine in DMF) without disturbing acid-labile side-chain protecting groups or the peptide-resin linkage.
This orthogonal deprotection chemistry is what makes automated, high-throughput peptide synthesis possible.
2. The PEG2 Spacer: Distance MattersThe diethylene glycol (PEG2) segment — those two ethoxy units tucked between the Fmoc-protected amine and the carboxylic acid — is not just filler. In biochemical terms, even a short PEG spacer can:
--Increase aqueous solubility of conjugated hydrophobic peptides.
--Reduce non-specific binding by shielding hydrophobic surfaces.
--Improve pharmacokinetics by slowing renal clearance and enzymatic degradation.
--Provide conformational flexibility, allowing tethered ligands to reach their binding pockets without steric hindrance.
3. The Terminal Carboxylic Acid: A Universal HandleThe free -COOH group at the distal end is the reactive warhead. It can be activated with standard coupling reagents (HBTU, HATU, DIC/HOBt) and attached to virtually any amine-bearing surface, scaffold, or growing peptide chain.
This versatility means CAS 166108-71-0 does not limit your synthetic strategy — it expands it.
Where This Compound Earns Its Keep: Key Applications
--Peptide Nucleic Acid (PNA) Synthesis: Perhaps the most scientifically elegant application of Fmoc-8-amino-3,6-dioxaoctanoic acid is in the synthesis of peptide nucleic acids (PNAs).
PNAs are synthetic DNA/RNA mimics in which the charged sugar-phosphate backbone of natural nucleic acids is replaced by a neutral, peptide-like N-(2-aminoethyl)glycine scaffold.
The Koskinen group at the University of Helsinki demonstrated that incorporating PEG spacers via Fmoc-NH-PEG2-CH2COOH into PNA backbones can modulate helical conformation and improve solubility — critical for antisense and antigene therapeutic applications.
Researchers building substituted PNAs routinely use this linker as a key monomer unit.
--Antibody-Drug Conjugates (ADCs) and Bioconjugation: ADCs represent one of the fastest-growing segments in oncology, with drugs like Enhertu (trastuzumab deruxtecan) generating billions in annual revenue.
The linker chemistry that connects the antibody to the cytotoxic payload is often the difference between a therapeutic window and a toxicity disaster.Short PEG linkers like Fmoc-NH-PEG2-CH2COOH serve as hydrophilic spacers in ADC construct design.
The Fmoc group allows the linker to be incorporated into the payload or peptide spacer during solid-phase synthesis, after which it is deprotected to reveal the free amine for further elaboration or conjugation.
--Peptide Drug Candidates: From GLP-1 agonists reshaping the metabolic disease landscape to antimicrobial peptides fighting resistant infections, the peptide drug pipeline is deeper than ever.
Every peptide drug developer faces the same challenge: how to modify the native peptide to improve its drug-like properties without destroying its biological activity.PEGylation — the covalent attachment of PEG chains — is one of the most successful strategies.
Sometimes all you need is a two-unit PEG spacer at a specific position to solve a solubility or aggregation problem without compromising target engagement. That is exactly where Fmoc-NH-PEG2-CH2COOH shines.
--Diagnostic Probes and Fluorescent Conjugates:The terminal carboxylic acid can also be used to attach fluorescent dyes, biotin tags, or chelating groups (for radiometal complexation) to amine-functionalized biomolecules.
The PEG spacer ensures that the bulky reporter group does not interfere with the biological recognition event being studied.
Fmoc-8-Amino-3,6-Dioxaoctanoic Acid is a multi-functional building block featuring an Fmoc protecting group, a short PEG spacer, and a terminal carboxylic acid.
It is widely used in peptide therapeutics, PNA synthesis, and antibody-drug conjugates to improve solubility, stability, and synthetic flexibility. Despite its modest appearance, this compound plays a critical enabling role in modern pharmaceutical development.
Product manager: Joy Wu Contact/Email address: Joy@coreychem.com
