HGH Fragment 176-191 vs AOD-9604: A Research Comparison
HGH Fragment 176-191 and AOD-9604 are almost the same molecule: AOD-9604 is the 176-191 fragment with its N-terminal phenylalanine substituted by tyrosine. Both are studied within lipolysis and growth hormone structure-activity research. Their research trajectories differ, with AOD-9604 having been carried into human clinical study as a metabolic candidate while the unmodified fragment is chiefly a preclinical reference. Both are supplied for research use only.
The core difference: one N-terminal substitution
The two compounds are nearly identical. HGH Fragment 176-191 is the C-terminal 176-191 region of human growth hormone, the portion associated in research with the hormone's lipolytic activity but not its growth-promoting, IGF-1-raising activity. AOD-9604 is that same 16-residue fragment with its N-terminal phenylalanine replaced by tyrosine, a substitution introduced to aid synthesis and stability. Because tyrosine differs from phenylalanine by a single hydroxyl oxygen, both molecules remain 16 residues long and that one-atom substitution is the defining structural difference between the two.
Structure and molecular profile
Both fragments are 16-residue peptides that retain the native cysteine-cysteine disulfide bridge of the parent hormone region. HGH Fragment 176-191 has a molecular weight near 1799.1 g/mol; AOD-9604 has a molecular weight near 1815.1 g/mol, the roughly 16 g/mol difference reflecting the single oxygen atom that the phenylalanine-to-tyrosine substitution adds. Confirm exact values against each Certificate of Analysis.
Clinical and regulatory context
AOD-9604 was developed as a metabolic drug candidate and has been investigated in human clinical research within obesity and body-composition endpoints, including Phase 2 obesity trials, and it did not go on to become an approved medicine. HGH Fragment 176-191, the unmodified parent fragment, is studied predominantly in preclinical lipolysis and structure-activity models. Neither is an approved drug, and both are supplied as research-use-only materials.
How each is studied
Both are studied within adipocyte lipolysis, fat-metabolism models, and GH structure-activity work that asks which part of the hormone carries the metabolic signal. Because they differ by only a single N-terminal substitution, they are frequently run side by side, with the phenylalanine-to-tyrosine change of AOD-9604 treated as the experimental variable of interest. A protocol chooses AOD-9604 when the stabilized analog is preferred and the unmodified fragment when the native 176-191 reference is needed.
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