Adenosine | CAS 58-61-7 | ≥98%

Adenosine (β-D-adenosine, Ado) is the canonical purine ribonucleoside formed by adenine linked to D-ribofuranose through a β-N9-glycosidic bond. In RNA, adenosine residues pair with uridine through Watson–Crick hydrogen bonding and typically adopt the anti glycosidic orientation and C3'-endo sugar pucker characteristic of A-form helices. Within the cell it sits at a metabolic crossroads: phosphorylation by adenosine kinase routes it into the AMP/ADP/ATP pool, while its adenosine/adenylate architecture is embedded in cAMP, S-adenosylmethionine, NAD+, FAD, and coenzyme A. This places adenosine at the intersection of nucleic-acid, energy, signalling, and cofactor chemistry, and at the centre of salvage-pathway research and chemoenzymatic synthesis of adenine nucleotides.

Adenine Nucleotide Pool and Energy Charge

Adenosine kinase (ADK; EC 2.7.1.20) is a high-affinity, low-capacity ATP:adenosine 5'-phosphotransferase, with reported Km values in the submicromolar-to-low-micromolar range, that drives the committed step of purine ribonucleoside salvage: ATP + adenosine → ADP + AMP. The reverse arm is run by cytosolic 5'-nucleotidase (cN-I; EC 3.1.3.5), and the two enzymes form a tight substrate cycle in which small fluctuations in ADK activity translate into large changes in ambient adenosine. Because intracellular AMP/ADP/ATP sit in the millimolar range while free adenosine sits in the nanomolar range, ADK maintains the cytosol as a sink for extracellular adenosine entering through equilibrative (hENT1/2; SLC29 family) and concentrative (hCNT1–3; SLC28 family) nucleoside transporters. AMP generated by ADK is interconverted with ADP and ATP by adenylate kinase and nucleoside diphosphate kinase, feeding the adenylate energy charge and ATP-regeneration networks. Adenosine is therefore a defining substrate in ADK kinetic assays, in HPLC/LC-MS profiling of the adenine nucleotide pool, and in studies of energy-charge homeostasis under hypoxia or metabolic stress.

cAMP Generation and P1 (Adenosine) Receptor Signalling

ATP is the direct substrate of adenylyl cyclase, which generates 3',5'-cyclic AMP and pyrophosphate; cAMP is then hydrolysed by phosphodiesterases to 5'-AMP. Adenosine itself is the endogenous agonist of the four P1 receptor GPCRs: A1 and A3 couple to Gi/o and inhibit adenylyl cyclase, while A2A and A2B couple to Gs and stimulate it. The downstream cAMP–PKA–CREB axis intersects with direct ion-channel modulation (A1-mediated regulation of cardiac K+ and N/P/Q-type voltage-gated Ca2+ channels) and with Gβγ-driven MAPK and phospholipase C pathways. Cytosolic ADK and extracellular ecto-5'-nucleotidase (CD73) together set the local adenosine concentration that feeds these receptors, which is why ADK-level perturbation translates so directly into receptor-level readouts. Adenosine serves as the reference agonist in P1-receptor pharmacology, used alongside subtype-selective ligands, phosphodiesterase inhibitors, and adenylyl-cyclase activators to separate cyclic-nucleotide synthesis from degradation.

SAM/SAH Methylation Cycle

S-adenosylmethionine (SAM) is the principal biological methyl donor; more than fifty SAM-dependent methyltransferases transfer its activated methyl group to DNA, RNA, histone, protein, lipid, and small-molecule substrates, releasing S-adenosylhomocysteine (SAH) as the obligate by-product. SAH is hydrolysed to adenosine and L-homocysteine by S-adenosylhomocysteine hydrolase (SAHH/AHCY; EC 3.13.2.1), an NAD+-dependent tetrameric enzyme whose intrinsic equilibrium actually favours SAH synthesis; in vivo, the reaction runs in the hydrolytic direction only because adenosine is rapidly removed by ADK and adenosine deaminase (ADA; EC 3.5.4.4) and homocysteine by transsulfuration and remethylation. Adenosine accumulation therefore drives SAH up, depresses the SAM/SAH ratio, and product-inhibits cellular methyltransferases — placing ADK at the centre of the link between purine homeostasis and global transmethylation capacity. Adenosine is the canonical product standard in SAHH activity assays and in LC-MS profiling of one-carbon and methionine-cycle metabolites.

Adenylyl Transfer in NAD+, FAD, and Coenzyme A Biosynthesis

The adenylyl group donated by ATP is transferred onto three of the most important cofactor systems in metabolism. Nicotinamide mononucleotide adenylyltransferase (NMNAT; EC 2.7.7.1) condenses NMN with ATP to give NAD+ and pyrophosphate; FAD synthetase (FADS/FLAD1; EC 2.7.7.2) performs the equivalent reaction on FMN to give FAD; and phosphopantetheine adenylyltransferase (PPAT; EC 2.7.7.3) adenylylates 4'-phosphopantetheine on the way to coenzyme A. Adenylyl–pyrophosphate displacement is the recurring chemistry across this family. Adenosine and its nucleotides are therefore foundational reference materials in studies of NAD+ biosynthesis and salvage, FAD-dependent oxidoreductases, CoA-mediated acyl transfer, and the NAD+-consuming enzyme classes that sit downstream — sirtuins (NAD+-dependent deacylation/deacetylation and ADP-ribosylation), poly(ADP-ribose) polymerases (mono- and poly-ADP-ribosylation), and CD38 (NAD+ hydrolysis and cyclic ADP-ribose generation).

Spectroscopic and Chemoenzymatic Reference

Adenosine has a UV absorption maximum near 260 nm with ε ≈ 15,400 M−1cm−1 at neutral pH, providing direct concentration determination by UV spectrophotometry and serving as the per-base extinction reference for A-rich oligonucleotide quantification. 1H NMR signatures are diagnostic: the H1' anomeric proton at δ ≈ 5.9–6.0 ppm in D2O, and the adenine H8 and H2 singlets in the δ 8.1–8.4 ppm region. Reverse-phase C18 HPLC with UV detection at 254/260 nm, and ion-pair LC-MS protocols, use adenosine as a primary retention and quantitation standard for purine ribonucleosides. ADK accepts a remarkably broad range of base- and sugar-modified analogues, and SAHH accommodates 3'-modified adenosine analogues such as cordycepin (3'-deoxyadenosine) — making adenosine a benchmark substrate for chemoenzymatic preparation of nucleotide cofactors and modified adenine derivatives used in synthetic RNA chemistry.

Other Applications

• Reference standard for HPLC and LC-MS profiling of purine nucleosides and nucleotides
• Substrate for adenosine kinase, adenosine deaminase, and S-adenosylhomocysteine hydrolase activity assays
• Purine ribonucleoside supplement in defined-media and salvage-dependent culture systems
• Starting material for chemoenzymatic synthesis of AMP/ADP/ATP, cAMP, NAD+, and modified adenine nucleotides
• Reference compound for 1H, 13C, and 31P NMR studies of nucleoside conformation and glycosidic-bond geometry
• Building block for solid-phase oligonucleotide synthesis via N6-protected, 5'-O-DMTr, 2'-O-protected, 3'-O-phosphoramidite derivatives