Selank

Covalent structure (atoms, bonds, charges and stereochemistry): PubChem CID 11765600, cross-checked against the FDA Global Substance Registration System record for SELANK. The 3D coordinates are a computed conformer (RDKit ETKDG distance-geometry embedding followed by MMFF94 force-field minimisation), not an experimental structure.

All 110 atoms, including 57 hydrogens, are generated from the PubChem structure with explicit hydrogens added; the protonation state is exactly the PubChem record's (neutral, no formal charges). 106 conformers were embedded with RDKit 2025.09.2 ETKDGv3 (fixed random seed) and each was minimised with the MMFF94 force field. The lowest-energy conformer without atomic clashes and every amide bond trans (6 checked) was kept (MMFF94 -21.1 kcal/mol); it is the best of 106 sampled conformers, not a proven global minimum, and not a solution or crystal structure. The model was then re-centred and rotated to its principal axes. No atom position is experimental, so every atom has PDB occupancy 0.00. Formula, mass, bond graph, stereocentres and InChIKey were re-derived from the published coordinate file and agree with PubChem. Ring closures were re-checked in the written file: no disulfide bonds or macrocycles; the configuration of every amino-acid alpha carbon was re-derived from the coordinates. The stereochemistry was also confirmed by assembling the molecule residue by residue from the stated sequence, with every D and L residue written explicitly, and matching its InChIKey to the modelled structure's. Selank is a heptapeptide made of tuftsin (Thr-Lys-Pro-Arg) followed by the tripeptide Pro-Gly-Pro. Modelled as the neutral free peptide (amines, carboxylic acid and guanidine un-ionised), which is the form the formula and mass describe; salts such as the acetate are not modelled. This single conformer is a prediction of one plausible shape of a flexible peptide, not an experimental structure and not evidence of the shape the peptide adopts in solution or in the body.

7 defined stereocentres, each matching PubChem; CIP labels re-derived from the published coordinates agree with the source structure. Amino-acid alpha carbons re-derived from the published coordinates: 6 L. Checked explicitly in the coordinates: Thr1 alpha carbon L; Lys2 alpha carbon L; Pro3 alpha carbon L; Arg4 alpha carbon L; Pro5 alpha carbon L; Pro7 alpha carbon L.