Over 100 RNA modifications have been discovered in nature. They play important roles in many biological systems. Some serve as an additional layer of regulation of various biological processes. Some are indispensable components of functional RNA structures. Errors related to them have been found to be the cause of many human diseases. Among the modifications, many are sensitive to basic and nucleophilic conditions. Because standard chemical RNA synthesis methods use acyl groups such as acetyl, isobutyryl and benzoyl groups to protect the exo-amino groups of nucleobases, and use the succinyl ester linker to anchor RNA to the solid support, RNA deprotection and cleavage have to be carried out under strongly basic and nucleophilic conditions. As a result, standard RNA synthesis methods cannot be used to synthesize RNAs containing sensitive epitranscriptomic modifications as well as artificially designed sensitive functional groups. An example of sensitive RNA modifications is N4-acetylcytidine (ac4C). It was first discovered in tRNAs and later rRNAs, where it is typically static under normal biological conditions, and is required for the RNAs to adopt their 3D structures for normal function. More recently, it was also discovered in mRNAs and even regulatory RNAs such as lncRNA, where it is typically dynamic, and being dynamic is needed for its intended biological functions. Errors related to ac4C are related to a wide range of human diseases such as various cancers, cardiovascular diseases, and aging. A chemical method that is suitable for the synthesis of RNAs containing ac4C at any site without any sequence restrictions would open doors for projects aimed to answer a wide range of fundamental biological questions regarding ac4C. In addition, ac4C, as well as the non-natural ac2G and ac6A, can potentially increase nucleic acid duplex stability significantly. A site-specific method for the synthesis of ac4C-containing RNAs would enable studies of their applications in antisense, siRNA and gRNA therapeutics. However, the ac4C modification cannot withstand the basic and nucleophilic conditions (e.g. 10 M methylamine in ethanol/water v/v 1:1 ) used by standard RNA synthesis methods for deprotection and cleavage, and therefore standard methods are not suitable for the synthesis of RNAs containing ac4C.