# B7-33

> A 27-residue single-chain relaxin-2 analog and selective RXFP1 agonist — a simplified relaxin mimetic studied for anti-fibrotic effects.

- Also known as: Single-chain relaxin, relaxin B7-33
- Class: Healing & Repair
- FDA approved: No
- Canonical page: https://americanpeptide.com/catalog/b7-33

## Overview

B7-33 is a single-chain peptide derived from the B-chain of human relaxin-2, the hormone best known for remodeling connective tissue in pregnancy. Native relaxin is a complex two-chain, disulfide-linked hormone that is hard to make; B7-33 strips it down to a single 27-residue chain that still activates relaxin’s main receptor, RXFP1. Its research interest is anti-fibrotic: like relaxin, it has reduced or reversed scarring (fibrosis) in preclinical heart and lung models, but as a far simpler, more manufacturable molecule.

B7-33 is an exercise in simplification. Human relaxin-2 is a powerful anti-fibrotic hormone, but it is a two-chain, disulfide-linked protein — expensive and difficult to produce, which has long limited its therapeutic use. Researchers at the Florey Institute engineered B7-33 as a minimal single-chain version: a 27-residue peptide based on relaxin’s B-chain that dispenses with the second chain while still switching on the relaxin receptor RXFP1.

What makes it notable is that the simplification did not cost the biology. In preclinical rodent models of heart and lung disease, B7-33 prevented or reversed fibrosis with potency similar to native relaxin, apparently through a functionally selective signal (via RXFP1–AT2 receptor complexes) that favors the collagen-degrading enzyme MMP-2. That combination — relaxin-like anti-fibrotic activity in a small, synthesizable peptide — is why it draws interest as a research compound. It is not FDA-approved.

## Mechanism

Functionally selective agonist of the relaxin receptor RXFP1 — signaling (in part via RXFP1–angiotensin II type-2 receptor heterodimers) toward pERK1/2 and the collagen-degrading enzyme MMP-2, driving anti-fibrotic remodeling.

## Chemistry

| Property | Value |
| --- | --- |
| CAS number | 1818415-56-3 |

## Research areas

Studied in: Fibrosis, Cardiac repair, Pulmonary fibrosis, Tissue remodeling.

Guides on this site:

- [Wound Healing & Tissue Repair](https://americanpeptide.com/research-areas/wound-healing): Regenerative peptides studied for soft-tissue, tendon, and vascular repair.

## Key research

- Single-chain relaxin mimetic — a 27-residue analog of the relaxin-2 B-chain that activates RXFP1 without relaxin’s two-chain, disulfide-linked architecture.
- Anti-fibrotic — prevented or reversed fibrosis in preclinical heart and lung models with potency similar to native relaxin.
- Functionally selective signaling — proposed to act via RXFP1–angiotensin II type-2 receptor heterodimers toward pERK1/2 and MMP-2 (collagen degradation).
- Manufacturability — a small synthetic peptide, far simpler to make than the native two-chain hormone.
- Investigational — a research compound; not FDA-approved.

## Storage, handling & synthesis

**Synthesis.** B7-33 is a 27-residue single-chain analog of the relaxin-2 B-chain — a deliberate simplification of native relaxin’s two-chain, disulfide-linked structure that makes it a practical linear solid-phase peptide. Coupling efficiency and deletion-sequence removal over its length are the main quality considerations.

## FAQs

### What is B7-33?

B7-33 is a 27-residue single-chain analog of the relaxin-2 B-chain that activates the relaxin receptor RXFP1, studied as a simplified, anti-fibrotic relaxin mimetic.

### How is it different from natural relaxin?

Native relaxin-2 is a two-chain, disulfide-linked protein that is hard to make; B7-33 is a single 27-residue chain that still activates RXFP1, so it is far simpler to synthesize.

### What is it studied for?

Chiefly fibrosis — it reduced or reversed scarring in preclinical heart and lung models — along with broader tissue-remodeling research.

### Is B7-33 approved?

No — it is an investigational research compound, not FDA-approved. This page is a research and educational reference.

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Source: AmericanPeptide.com — https://americanpeptide.com/catalog/b7-33
Data license: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Attribution: AmericanPeptide.com.
Research reference only — computational and educational content, not medical advice.