CJC-1295

CJC-1295 names two different molecules, and unlike most naming collisions this one is not a matter of loose usage — both variants were developed deliberately, differ by a single appended residue, and are roughly 279 daltons apart. Resolving which one is in the vial is the first thing this page does.

The two variants

The only structural difference is the appended maleimide-bearing lysine, and it accounts for the entire mass gap. Both variants share an identical 29-residue backbone.

“DAC” stands for drug affinity complex. The maleimide is a thiol-reactive handle intended to form a covalent bond with a free cysteine thiol on serum albumin. That is a description of the chemistry the group was designed to perform — a maleimide is a standard bioconjugation reagent for thiol coupling — and nothing beyond that should be read into it.

We do not publish a single molecular weight or registry number for this listing. The certificate of analysis for the lot states which variant it is.

A genuinely disputed registry number

The no-DAC variant has no agreed CAS number. Cayman and GlpBio use 446036-97-1; ChemicalBook, Chemsrc and Alfa Chemistry use 863288-34-0 — for an identical structure. Neither Cayman product page lists a CAS at all.

This is not a case where one source is simply wrong. Rather than pick a side, we omit a CAS for this listing. A supplier quoting one confidently is expressing more certainty than the registry supports.

Structure

Both variants share a tetrasubstituted GRF(1–29) backbone. Relative to native sermorelin, four positions are changed:

• Ala2 → D-Ala. Inverting the stereocentre at position 2 blocks dipeptidyl peptidase-4 cleavage, which occurs between residues 2 and 3.
• Asn8 → Gln. Asparagine is prone to deamidation and to succinimide-mediated backbone rearrangement; substituting glutamine removes that degradation route.
• Gly15 → Ala. A conformational substitution — glycine is the most flexible residue and alanine restricts the local backbone.
• Met27 → Leu. Leucine is isosteric with methionine but has no sulfur. This removes the oxidation liability entirely, and it is why CJC-1295 is chemically more robust as a dry solid than sermorelin or tesamorelin, both of which retain Met27.

Read together, the four substitutions are a systematic removal of every obvious chemical and enzymatic liability in the parent sequence. The DAC variant then adds the lysine and its maleimide at the C-terminus.

Specification and characterisation

• Mass confirmation is the discriminating test between the variants: ~3647 against ~3368. As with TB-500, one measurement settles the identity question.
• RP-HPLC purity at 214 nm; 280 nm informative via the tyrosines.
• For the DAC variant — maleimide integrity. This is the specification point unique to CJC-1295 and the one most often missing. Maleimides hydrolyse to the corresponding maleamic acid, particularly at alkaline pH and in aqueous storage. The hydrolysed product is +18 Da and is no longer thiol-reactive — the material looks nearly intact by mass but has lost the function the DAC group exists to provide. A certificate for DAC material that does not address maleimide integrity has not characterised the feature that distinguishes the product.
• Amidation completeness for the no-DAC variant — the free acid differs by +1 Da.
• Deletion sequences across a 29- or 30-residue synthesis.
• Counter-ion. Note that reference catalogues list the two variants in different salt forms — the DAC material as a trifluoroacetate, the no-DAC material as an acetate. That is a salt difference, not a structural one, but it affects net peptide content.

Handling and stability

Store sealed at 2–8 °C, dry, protected from light. Equilibrate in a desiccator before opening.

The Met27→Leu substitution means oxidation is not the concern here that it is for the other GHRH analogues. For DAC material the dominant concern is maleimide hydrolysis, which is accelerated by moisture and by alkaline conditions — so keeping the solid genuinely dry matters more for this compound than for most, and aqueous storage is particularly unsuitable.

Related compounds in this library

Sermorelin is the unmodified parent fragment; tesamorelin solves the same N-terminal problem by acylation of the full-length hormone. The sermorelin page sets the three out side by side.

References

Chemical, specification and analytical sources. This list is deliberately limited to chemistry and analytical references.

• Cayman Chemical 31497, CJC-1295 DAC trifluoroacetate — formula, molecular weight, salt form
• Cayman Chemical 32704, CJC-1295 acetate (Mod GRF 1-29) — formula, molecular weight, salt form
• ChemicalBook and Chemsrc — conflicting registry numbers, as discussed above
• Bachem, Handling and Storage Guidelines for Peptides — lyophilised solid handling, moisture sensitivity

Cosmic Aminos supplies this material as a laboratory reagent for in-vitro research use only. It is not a drug, food, cosmetic or dietary supplement, is not approved by the Food and Drug Administration for any use, and is not for human or veterinary consumption. No dosing, administration or preparation guidance is provided.