### Chemical Synthesis of NTPs and Their Analogs  
Since the first laboratory synthesis of ATP in 1949, researchers worldwide have worked to develop efficient routes for synthesizing 5\({}^{\prime}\)-NTPs and their analogs [50]. To this day, the most widely used chemical methods are based on protocols established by [PERSON] and [PERSON]. The [PERSON] method [81] involves the selective 5\({}^{\prime}\)-monophosphorylation of a nucleoside precursor (2,3\({}^{\prime}\)-O-iso-propylidene nucleoside) using electrophilic phosphorous oxychloride (POCI\({}_{3}\)) [10]. The resulting phosphorodichlorate intermediate is then reacted with pyrophosphate to form the cyclic triphosphate, which is ultimately hydrolyzed to yield the desired product. In contrast, the [PERSON] method [82], a \"one-pot, three-step\" process, employs 3\({}^{\prime}\)-O-protected nucleoside precursors (with 2\({}^{\prime}\)-O protection for NTPs) [10]. These precursors react with salicyl phosphorochlorite to form an activated phospholite intermediate. Two nucleophilic substitution reactions, initiated by tris(tetra-n-butylammonium) hydrogen pyrophosphate, produce the cyclic intermediate. Finally, iodine-mediated oxidation of this intermediate yields the modified (d)NTP. The Ludwig-Eckstein method offers the advantage of reducing undesired byproducts, simplifying the subsequent HPLC purification process.  
The Ludwig method has undergone significant refinement, with considerable efforts directed at improving its efficiency. Modifications included the use of a proton sponge to protect acid-sensitive products [83] or adjustments such as lowering the temperature (from 0 \({}^{\circ}\)C to \(-\)15 \({}^{\circ}\)C) [84]. Further advancements included an enhanced Eckstein method, which employed bulkier 5\({}^{\prime}\)-phosphitylation reagents for more specific reactions, yielding 5\({}^{\prime}\)-NTPs in a one-pot, protection-free process [85]. Supported solution synthesis methods also emerged, focusing on reducing purification steps [2; 86]. These approaches involve immobilizing substrates or phosphorylation agents onto insoluble resins or soluble polymers, making it easier to remove byproducts. However, attaching the base or sugar moiety of the nucleoside/nucleotide to the support limits this method to substrates without modifications to these parts. Additionally, further column purification is required to achieve product purity greater than 95%.  
Several comprehensive reviews have explored the various chemical methods used in 5\({}^{\prime}\)-NTP synthesis over the decades and are recommended for further reading. Early works detail the first decades of research [87], while later reviews summarize chemical production processes and their applications [50; 86; 88]. More recent developments in the field are thoroughly discussed in newer publications [2; 17].  
Ongoing advancements in chemical methods have made it possible to efficiently and selectively produce a wide range of 5\({}^{\prime}\)-NTPs. However, some challenges persist, including the need for anhydrous reagents, multiple reaction steps, highly variable yields depending on substrate modifications, and the use of hazardous reagents and harsh conditions. No universal chemical method for 5\({}^{\prime}\)-NTP synthesis has been established yet, and for each desired product, the most suitable reaction route and conditions must be carefully evaluated.