Guanosine (G), also known as 2-amino-inosine, belongs to the class of organic compounds known as purine nucleosides. Purine nucleosides are compounds comprising a purine base attached to a ribosyl or deoxyribosyl moiety. Guanosine consists of a guanine attached to a ribose (ribofuranose) ring via a beta-N9-glycosidic bond. Guanosine is a moderately basic compound (based on its pKa). Guanosine exists in all living species, ranging from bacteria to humans. In humans, guanosine is involved in intracellular signalling through adenosine receptor A2B and adenosine. Outside of the human body, guanosine has been detected, but not quantified in, several different foods, such as leeks, garlic, chicory roots, green bell peppers, and black-eyed peas. This could make guanosine a potential biomarker for the consumption of these foods. Guanosine plays an important role in various biochemical processes such as the synthesis of nucleic acids and proteins, photosynthesis, muscle contraction, and intracellular signal transduction (cGMP). Guanosine is a potentially toxic compound. It is very soluble in acetic acid, slightly soluble in water, and insoluble in ethanol, diethyl ether, benzene, and chloroform. The antiviral drug acyclovir, often used in herpes treatment, and the anti-HIV drug abacavir, are both structurally similar to guanosine. Guanosine was also used to make regadenoson. Guanosine is a white, crystalline powder with no odour and a mild saline taste. Guanosine is required for an RNA splicing reaction in mRNA when a "self-splicing" intron removes itself from the mRNA by cutting at both ends, re-ligating, and leaving just the exons on either side to be translated into protein. When guanine is attached by its N9 nitrogen to the C1 carbon of a deoxyribose ring it is known as deoxyguanosine. Guanosine can be found in clovers, coffee plants, and the pollen of pines. Guanosine can be phosphorylated to become guanosine monophosphate (GMP), cyclic guanosine monophosphate (cGMP), guanosine diphosphate (GDP), and guanosine triphosphate (GTP).