Pires, Patricia C. team published research in European Journal of Pharmaceutical Sciences in 2021 | 111-90-0

111-90-0, Diethylene glycol monoethyl ether appears as a colorless, slightly viscous liquid with a mild pleasant odor. Flash point near 190°F. Used to make soaps, dyes, and other chemicals.
Diethylene glycol monoethyl ether is a primary alcohol that is ethanol substituted by a 2-ethoxyethoxy group at position 2. It has a role as a protic solvent. It is a diether, a primary alcohol and a hydroxypolyether. It derives from a diethylene glycol., Computed Properties of 111-90-0

Ethers feature bent C–O–C linkages. In dimethyl ether, the bond angle is 111° and C–O distances are 141 pm. 111-90-0, formula is C6H14O3, Name is Diethylene Glycol Monoethyl Ether. The barrier to rotation about the C–O bonds is low. The bonding of oxygen in ethers, alcohols, and water is similar. In the language of valence bond theory, the hybridization at oxygen is sp3. Computed Properties of 111-90-0.

Pires, Patricia C.;Fazendeiro, Ana C.;Rodrigues, Marcio;Alves, Gilberto;Santos, Adriana O. research published 《 Nose-to-brain delivery of phenytoin and its hydrophilic prodrug fosphenytoin combined in a microemulsion – formulation development and in vivo pharmacokinetics.》, the research content is summarized as follows. Phenytoin is a low aqueous solubility antiepileptic drug, but its phosphate ester prodrug fosphenytoin is soluble, although less permeable. In a previous study, the intranasal administration of aqueous-based formulations of fosphenytoin led to high but delayed phenytoin bioavailability compared to the i.v. route. In this work, we hypothesized that formulating an association of the prodrug fosphenytoin and the drug phenytoin (the active and diffusible form), could result in a faster and/or more effective brain targeting. Hence, nano or microemulsions containing both active drug and prodrug were developed and characterized regarding viscosity, osmolality, pH, mean size and in vitro drug release. Then, in vivo pharmacokinetics of a selected microemulsion containing fosphenytoin and phenytoin was evaluated in mice following intranasal administration and compared with a similar microemulsion containing fosphenytoin only. Both microemulsions led to higher brain drug levels at short time points than previously developed simpler aqueous based fosphenytoin formulations, likely due to the microemulsion′s permeation enhancing effect. In addition, having a small amount of phenytoin in the formulation led to an equivalent maximum brain drug concentration and an overall higher absolute bioavailability, with a prolonged drug exposure. Hence, it can be concluded that if there is a need for a fast and prolonged therapeutic effect, a drug/phosphate ester prodrug combination in a microemulsion is ideal, but if a fast effect is all that is needed, having the prodrug alone could be enough, while considering a formulation with permeation enhancing components.

111-90-0, Diethylene glycol monoethyl ether appears as a colorless, slightly viscous liquid with a mild pleasant odor. Flash point near 190°F. Used to make soaps, dyes, and other chemicals.
Diethylene glycol monoethyl ether is a primary alcohol that is ethanol substituted by a 2-ethoxyethoxy group at position 2. It has a role as a protic solvent. It is a diether, a primary alcohol and a hydroxypolyether. It derives from a diethylene glycol., Computed Properties of 111-90-0

Referemce:
Ether – Wikipedia,
Ether | (C2H5)2O – PubChem