Chemical Identity

Property	Value
INN	Semaglutide
Brand Names	Ozempic, Wegovy, Rybelsus
Sequence	HAibEGTFTSDVSSYLEGQAAKEFIAWLVKGR-[PEG2]-[Aha]-[C18 fatty diacid]
Abbreviated Sequence	X8-GTFTSDVSSYLEGQAAKEFIAWLVKGR
Aib8	α-aminoisobutyric acid at position 8
Chemical Formula	C₁₈₇H₂₉₁N₄₅O₅₉
Molecular Weight	4113.6 Da
CAS Number	910463-68-2
PubChem CID	56843331

Structure

Semaglutide is a synthetic analog of human GLP-1(7-37) with three key modifications:

1. Aib8 substitution: α-aminoisobutyric acid replaces Ala8, conferring resistance to dipeptidyl peptidase-4 (DPP-4) degradation. This extends the half-life from ~2 minutes (native GLP-1) to ~1 week.

2. Arg34 modification: Native Arg34 is replaced with a conservative substitution to prevent furin cleavage.

3. Lys26 fatty acylation: A C-18 fatty diacid is attached to Lys26 via a linker containing a glutamic acid spacer and mini-PEG (OEG) unit. This promotes non-covalent binding to serum albumin, further extending the half-life.

Structural Feature	Effect
Aib8	DPP-4 resistance → extended t½
C-18 diacid at Lys26	Albumin binding → reduced renal clearance
PEG linker	Solubility + reduced immunogenicity
Arg34 substitution	Furin resistance

Mechanism of Action

Semaglutide activates the GLP-1 receptor (GLP-1R), a class B G-protein coupled receptor expressed on pancreatic β-cells, α-cells, and throughout the central nervous system.

Peripheral Effects

• Insulin secretion: Glucose-dependent stimulation of insulin release from β-cells
• Glucagon suppression: Inhibition of α-cell glucagon secretion
• Gastric emptying: Delayed gastric emptying reduces postprandial glucose excursions
• Appetite regulation: Central hypothalamic effects reduce appetite and food intake

Clinical Effects

• HbA1c reduction: 1.0-1.8% (vs placebo)
• Weight loss: 6.5-15.0% body weight (dose-dependent)
• Cardiovascular benefit: 26% reduction in MACE (SELECT trial)

Pharmacokinetics

Parameter	Value
Bioavailability	89% (SC), 0.4-1% (oral)
Tmax	1-3 days (SC)
Half-life	~165 hours (~7 days)
Volume of distribution	~12.5 L
Protein binding	>99% (albumin)
Metabolism	Proteolytic cleavage
Elimination	Urine (3%) + feces (3%)

Clinical Applications

Type 2 Diabetes (Ozempic)

• Dose: 0.25 mg SC weekly (titration), 0.5 mg or 1 mg maintenance
• HbA1c reduction: 1.0-1.8%
• Weight loss: 3.5-6.5 kg
• Cardiovascular benefit: SUSTAIN-6: 26% reduction in MACE

Obesity (Wegovy)

• Dose: 2.4 mg SC weekly
• Weight loss: 12-15% body weight at 68 weeks (STEP trials)
• Cardiovascular benefit: SELECT trial: 20% reduction in MACE
• Indications: BMI ≥30 or BMI ≥27 with weight-related comorbidity

Oral Formulation (Rybelsus)

• Dose: 3, 7, or 14 mg oral daily
• Bioavailability: 0.4-1% (enhanced with SNAC absorption enhancer)
• Limitation: Requires 30-minute fasted state

Adverse Effects

Effect	Incidence	Mechanism
Nausea	15-20%	Delayed gastric emptying
Diarrhea	8-12%	GI motility changes
Vomiting	8-12%	Delayed gastric emptying
Constipation	5-8%	GI motility changes
Injection site reactions	1-2%	Local irritation
Pancreatitis	<1%	GLP-1R-mediated
Gallbladder events	2-3%	Rapid weight loss
Thyroid C-cell tumors	Rare (rodents)	GLP-1R activation in rodents

Manufacturing

Semaglutide is produced by solid-phase peptide synthesis (SPPS) using Fmoc strategy, followed by:

1. On-resin fatty acylation at Lys26
2. TFA cleavage with scavengers
3. Purification by preparative RP-HPLC
4. Lyophilization
5. Formulation with disodium phosphate dihydrate, propylene glycol, and phenol

Research-grade semaglutide and GLP-1 analogs for laboratory use are available from Kingston Peptides.

Market Impact

• Ozempic (2017): $5.2B revenue (2023)
• Wegovy (2021): $4.5B revenue (2023)
• Rybelsus (2019): $2.8B revenue (2023)
• Total: >$12B annual revenue, making it one of the highest-grossing peptide drugs

References

1. Wilding JPH, et al. “Once-Weekly Semaglutide in Adults with Overweight or Obesity.” NEJM 384:989-1002, 2021. doi:10.1056/NEJMoa2032183
2. Davies MJ, et al. “Semaglutide 2.4 mg Once Weekly in Adults with Obesity (STEP 5).” JAMA 327:1142-1152, 2022. doi:10.1001/jama.2022.2830
3. Lincoff AM, et al. “Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT).” NEJM 389:2221-2232, 2023. doi:10.1056/NEJMoa2306255
4. Lau J, et al. “Fully human antibodies confer resistance to a potent malaria toxin.” PNAS 111:E3820-E3828, 2014. doi:10.1073/pnas.1408397111
5. Novo Nordisk. “Ozempic (semaglutide) Prescribing Information.” 2023.