B7-33

1 Identity

Relaxin-family peptide analogs. Not the same article as the lipidated derivative AcK(PalmGlu)-PEG12-B7-33 reported in Int J Mol Sci 2023, 24:6616, which is a different, heavier molecule.

Sequence

H-Val-Ile-Lys-Leu-Ser-Gly-Arg-Glu-Leu-Val-Arg-Ala-Gln-Ile-Ala-Ile-Ser-Gly-Met-Ser-Thr-Trp-Ser-Lys-Arg-Ser-Leu-OH (VIKLSGRELVRAQIAISGMSTWSKRSL). TWENTY-seven residues, not 26 - the residue count printed on the Wikipedia entry is wrong and the count is trivially checkable against the string. All L, linear, free N-terminal alpha-amino group, free C-terminal carboxyl, no acylation, no amidation. The two cysteines of the parent human H2 relaxin B-chain (B11 and B23) are replaced by serine, so this molecule contains no cysteine, no free thiol and no disulfide whatsoever; a certificate reporting a free-thiol titration or a disulfide assignment on this article has tested for something that is not present. Met19 and Trp22 are the two oxidation-labile residues. Six protonatable centers (N-terminal amine, Lys3, Arg7, Arg11, Lys24, Arg25) against only two carboxylates (Glu8 side chain and the C-terminal leucine), so counterion loading is high and net peptide content cannot be assumed.

Molecular formula

C131H228N40O37S (free acid)

Average mass

2987.57 Da (C131H228N40O37S), computed on IUPAC 2021 conventional atomic weights. Suppliers print 2987.52 for the same formula; that 0.05 Da difference is an atomic-weight-table artifact, not a structural disagreement, and neither number should be treated as a specification limit.

Monoisotopic mass

2985.6910 Da neutral. At 3 kDa the molecule is only observed multiply charged: [M+3H]3+ m/z 996.2376, [M+4H]4+ m/z 747.4300, [M+5H]5+ m/z 598.1455. The certificate must show a deconvoluted neutral mass with the raw charge envelope, not a single m/z.

Salt / variant note

(1) C-terminal amide, C131H229N41O36S, 2986.58 avg / 2984.70696 mono - exactly 0.984 Da below the free acid, and the live ambiguity in this market rather than a theoretical one, since sources in this market describe the article differently. On a 2.99 kDa molecule this shift is only resolvable from a deconvoluted high-resolution spectrum. (2) the parent cysteine form, VIKLCGRELVRAQIAICGMSTWSKRSL, C131H228N40O35S3, 3019.69 avg / 3017.64529 mono, +32.12 Da - a supplier who builds the native B-chain segment rather than the Cys-to-Ser analog delivers a different molecule that would additionally be capable of dimerizing through disulfide. (3) MET19 sulfoxide, +15.995 Da (C131H228N40O38S, 3003.57 avg / 3001.68590 mono), the predictable storage and workup degradant, and the sulfone at +31.990 Da. (4) TRP22 oxidation products, +15.995 and +31.990 Da, overlapping the methionine oxidation masses exactly - the two cannot be told apart by intact mass and require peptide mapping. (5) Truncations at the N-terminal end, in particular des-Val1 (-99.068 Da) and des-Val1-Ile2 (-212.152 Da), which are the usual failures on a 27-mer synthesis. (6) lipidated derivatives sold or published under related names, e.g. AcK(PalmGlu)-PEG12-B7-33, are separate heavier molecules and must not be released against this monograph.

2 Class & testing panel

Form

Single article

Testing panel

P1 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

Peer-reviewed primary literature exists and is small. The originating chemistry paper is Hossain MA et al., Chemical Science 2016;7:3805-3819 (DOI 10.1039/C5SC04754D). Subsequent peer-reviewed reports include a paper in the European Journal of Pharmacology 2017 (ScienceDirect S0014299917303059), an American Journal of Obstetrics and Gynecology 2016 abstract (S0002-9378(16)31706-9), a Journal of the American Heart Association 2020 paper (DOI 10.1161/JAHA.119.015748) and a lipidated-analog paper in the International Journal of Molecular Sciences 2023;24:6616. All identified reports are in-vitro or rodent. No ClinicalTrials.gov registration under 'B7-33' was identified, no controlled human trial was identified, and no marketing authorization exists in any jurisdiction. This is a description of what has been published and where, by study type and identifier.

4 Storage & specification

Storage

Lyophilized powder, -20 degrees C plus or minus 5 degrees C, desiccated with in-pack desiccant, sealed under nitrogen in amber or foil-overwrapped glass, protected from light. Photoprotection is a specification item and not a preference on this molecule because of the tryptophan indole; the nitrogen headspace is likewise a specification item because of the methionine. 2-8 degrees C is acceptable for transit and for working stock held no longer than 30 days. Vials are equilibrated to room temperature before opening.

Shelf life

Provisional 24 months at -20 degrees C plus or minus 5 degrees C, assigned by protocol and not measured. The interval is provisional pending a three-lot ICH Q1A study with an ICH Q1B option 2 photostability arm, long-term at -20 degrees C and accelerated at 25 degrees C and 60 percent relative humidity, with Met19 sulfoxide, Trp22 oxidation products and water content as the indicating attributes. The label is shortened on data and never extended without a completed dataset.