Quantum Chemical Modeling, Synthesis, Spectroscopic (FT-IR, Excited States, UV/VIS) Studies, FMO, QTAIM, ELF, LOL, NBO, NLO and QSAR Analyses of Nelarabine

: In this study, we report the results of experiments and density functional theory (DFT), time-dependent DFT, and quantitative structure-activity relationship (QSAR) analyses of (2R,3S,4S,5R)-2-(2-amino-6-methoxy-9H-purin-9-yl)-5-(hydroxymethyl) tetrahydrofuran-3,4-diol (nelarabine). The molecular geometry, vibrational modes, excited states, molecular electrostatic potential (MEP) maps were calculated and discussed. Frontier molecular orbitals (FMO), quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), localized orbital locator (LOL), natural charge, natural bonding, orbital (NBO) analysis were conducted and discussed. Nonlinear optical (NLO) and thermodynamic parameters were determined and discussed. In addition, Fourier transform infrared (FT-IR) and ultraviolet/visible (UV-Vis) spectral parameters were calculated and were found to agree with experimental spectral parameters excellently. The physicochemical, pharmacokinetic, and pharmacodynamic profiles were determined. The applicability of nelarabine as an anticancer drug was investigated in terms of QSAR models, and positive conclusions were yielded.


Introduction
Nucleosides are a group of naturally occurring molecules subunits of RNA and DNA. They are composed of nucleobase, purine or pyrimidine, and a five-carbon sugar. The purine bases include guanine and adenine, and the pyrimidine bases are uracil, thymine, and cytosine. The five-carbon sugar is deoxyribose or ribose in DNA or RNA, respectively. Nucleosides and their analogs have been long applied in medical and biochemical fields. Several nucleoside analogs have been clinically approved to treat different types of cancers, bacterial and fungal infections, and viral and parasitic diseases. Many other nucleosides are currently undergoing preclinical and clinical trials [1].
The optimized geometry of the lowest energy conformation of nelarabine is illustrated in Figure 1, with selected calculated bond lengths and angles listed in Table 1. The conformation with the lowest energy exhibits higher stability through hydrogen bonding relative to other low-energy conformations. The purine moiety exhibits shorter bonds and wider angles between bonds relative to the sugar moiety, implying greater charge delocalization and conjugation within the purine moiety relative to the sugar moiety.  Nelarabine consists of 36 atoms, which exhibit 102 normal modes of IR active vibrations. In the spectrum, peaks were observed in the 1000-1650 cm -1 range, attributed to C-N stretching, C=N stretching, C=C stretching, C-O stretching, N-H bending, O-H bending, and C-H bending. Moreover, the 2900-3500 cm-1 peaks are ascribed to O-H stretching, N-H stretching, and C-H stretching. Minor peaks are apparent in the 500-900 cm -1 fingerprint region, attributed to double and single bond bending and torsional vibrations. The theoretical IR spectrum is in excellent agreement with the experimental FT-IR spectrum ( Table 2). Molecular electrostatic potential (MEP) maps reflect regions with high or low electrostatic potential related to electron density and can be utilized to identify sites susceptible to electrophilic or nucleophilic attack and hydrogen bonding interactions [16][17][18]. The total electron density mapped with the electrostatic surface is illustrated in Figure 2. The negative sites with high electron density (prone to the electrophilic attack) are displayed in red, orange, and yellow. In contrast, the positive sites (which are prone to nucleophilic attack) are displayed in blue and cyan. The neutral regions are displayed in green. According to the MEP maps, the nitrogen and oxygen atoms in the modified purine moiety and the oxygen atoms in the sugar moiety are prone to electrophilic attack. The region between N12 and O20 on the modified purine moiety and the oxygen atoms in the sugar moiety exhibit the highest susceptibility to electrophilic attack. In contrast, the hydrogen atoms bonded to the nitrogen atom in the modified purine moiety. The hydrogen atoms bonded to the oxygen atoms on the sugar moiety exhibit the highest susceptibility to nucleophilic attack. All other regions are relatively neutral.

Electronic structure and excited states.
Twenty excited states of Nelarabine were calculated in ethanol and are listed in Table  3 [19,20]. The optimal transition was observed at λ = 213.46 nm, oscillator strength f = 0.404, which is attributed to a charge transfer (CT) of one electron into the excited singlet state (S0→S4), and is described by a wave function corresponding to the superposition of three configurations for the one-electron excitation: H-2→LUMO (21%), H-1→LUMO (54%), and HOMO→L+1 (18%). A transition at λ = 269.26 nm, oscillator strength f = 0.341 (S0→S1) is the second most optimal transition, described by a wavefunction corresponding to a configuration for the one-electron excitation: HOMO→LUMO. A transition at λ = 234.96 nm, oscillator strength f = 0.121 (S0→S2) is the third most optimal transition, which is described by a wavefunction corresponding to the superposition of three configurations for the one-electron excitation: H-2→LUMO (12%), H-1→LUMO (38%), HOMO→L+1 (43%). The shapes of the molecular orbitals involved in the λ max = 213.46, 234.96, and 269.26 nm transitions are presented in Figure 3. The theoretical excitation spectrum is in excellent agreement with the experimental UV-Vis spectrum of nelarabine in a 9:1 mixture of phosphate buffer (pH 7.0) and ethanol (absorption maxima at λmax = (210.8, 247.8, and 279.8 nm).

Frontier molecular orbital analysis and electronic properties.
FMO analysis was performed to investigate nelarabine's electronic properties, optical properties, and chemical reactivity. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are typically significant for electron donation and electron acceptance. The gas-phase electron density of the HOMO and LUMO are primarily localized on the modified purine moiety. The molecular orbitals in the gas phase and solution are relatively identical, except for energy gaps, which are smaller in ethanol (EHOMO ↑, ELUMO ↓). The path of the FMO electronic transitions (CT) in nelarabine is primarily within the modified purine moiety due to the presence of π bonds within the modified purine moiety.
The HOMO and LUMO energy levels (EHOMO and ELUMO) are related to the ionization potential (I = −EHOMO) and electron affinity (A = −ELUMO), respectively. The global hardness (η) is defined as the resistance of an atom or a group of atoms to CT. Electronegativity (χ) measures the power of an atom or a group of atoms to attract electrons. The electronic potential (μ) is a measure of the tendency of an electron in an atom or a group of atoms to escape its ground state. The chemical softness (S) measures the capacity of an atom or a group of atoms to receive electrons. Here, η, χ, μ, ω, and S were calculated using the following equations [21][22][23]: The results are listed in Table 4, along with the total electronic densities of states (DOSs) presented in Figure 4. The data reveals a high EHOMO-ELUMO energy gap and a low global hardness, which indicates the low reactivity and high kinetic stability of nelarabine. η = I-A/2 χ = I + A/2 μ = −(I + A)/2 ω = μ 2 /2η S = ½η  QTAIM was conducted to determine the nature of the chemical bonding in nelarabine at selected bond critical points (BCP). The topological parameters and molecular graph containing BCP are listed and illustrated in Table 5 and Figure 5, respectively. The topological parameters include electron density p(r), which describes the strength of a chemical bond, the Laplacian electron density ∇ 2 p(r), which determines where the electronic charge is locally concentrated or depleted, the electronic energy density H(r), which is defined as the sum of the kinetic and potential energy densities (G(r) and V(r), respectively). High positive values of p(r) indicate a stronger bond. Negative values of ∇ 2 p(r) and H(r) indicate covalent bonding, and positive values indicate non-covalent bonding. The ratio of V(r) to G(r) determines the nature of the interactions, where -V(r)/G(r) < 1 indicates weak interactions [24]. The results reveal three hydrogen bonds in nelarabine with low p(r), positive ∇ 2 p(r) values, and -V(r)/G(r) < 1 between N18-H26, O10-H31, and O7-H29, which are listed in terms of decreasing strength. The strongest individual covalent bond in nelarabine is the C11-N12 bond, p(r) = 0.37070 a.u., because of the increased confinement of π electrons between the two atoms. In contrast, the weakest bond is the O20-C21 bond because of its proximity to an electron-withdrawing moiety and its lack of conjugation.  The electron localization function (ELF) and localized orbital locator (LOL) analyses of nelarabine were performed; the results are summarized in Table 5 and illustrated for the planar modified purine moiety ( Figure 6). The ELF and LOL are visual descriptors that provide a visual representation of electron pair localization concerning a reference electron in a system in terms of a scalar field, with values ranging from 0 (blue) to 1 (red); higher values indicate perfect localization and lower values suggest electron gas-like behavior [25]. Bonding types can be distinguished from the EFL and LOL contour maps as well: the σ bond is oval, and the π bond is more extended or stretched perpendicular to the bond. Table 5 and Figure 6 data indicate that the electron pair localization is higher for the σ bonds between N-H and C-H and lone pairs than for π bonds on the planar modified purine moiety. However, the extent of π character on all other atoms suggests a high level of conjugation throughout the modified purine moiety, which implies that preferable electronic transitions (CT) occur within the moiety relative to transitions from or toward the moiety.

Natural charge analysis.
Considering that atomic charges determine many properties of molecular systems, the natural charges of nelarabine were computed by NBO analysis and are listed in Table 6. The carbon atoms on the modified purine moiety have positive and negative charges. Carbons C11, C14, C15, and C17, which are bonded to two or three electron-withdrawing nitrogen or oxygen atoms, have positive charges. Carbons C13 and C21, bonded to one electron-withdrawing nitrogen or oxygen atom, have negative charges. The most positively charged carbon atom in the modified purine moiety is C17 (0.61339), bonded to three electron-withdrawing nitrogen atoms. The most negatively charged carbon atom in the modified purine moiety is methyl C21 (-0.32346), bonded to one electron-withdrawing oxygen atom. Nitrogen and oxygen atoms in the modified purine moiety are negatively charged, with N19 (−0.83245) being the most negatively charged and N12 (−0.46842) being the least negatively charged atom among the nitrogen and oxygen atoms in the moiety. All carbon atoms on the sugar moiety are bonded to electron-withdrawing atoms and have positive and negative charges. Carbons C2, C3, C4, and C6 are bonded to one hydrogen atom and have positive charges, whereas C9 (−0.13051) is bonded to two hydrogen atoms and has a negative charge. The most positively charged carbon atom in the sugar moiety is C4 (0.25642), bonded to two electron-withdrawing nitrogen and oxygen atoms. Oxygen atoms in the sugar moiety have negative charges, with O7 (−0.77778) being the most negatively charged and O5 (−0.57932) the least negatively charged atom. All hydrogen atoms in nelarabine have positive charges, with H26 (0.50663) bonded to O7 on the sugar moiety being the most positively charged hydrogen atom and H28 (0.20155) bonded to C9 on the sugar moiety being the least positively charged hydrogen atom. Our natural charge analysis results agree with the findings of the MEP maps regarding the sites of susceptibility to electrophilic and nucleophilic attacks. NBO analysis was conducted to study the interactions between orbitals to obtain information regarding intramolecular CT, conjugation, hyperconjugation, and delocalization of the electron density. The calculated parameters, including occupation numbers, polarization coefficient values, intramolecular donor-acceptor interactions, and stabilization energies of selected bonds of nelarabine, are presented in Table S1-S2 (Supplementary Material).
The size of the polarization coefficients of the two-hybrid orbitals from atoms A and B demonstrates their importance in bond formation. The fraction of the hybrid orbital character between hybrids A and B, the fraction of the p character, and the non-bonding and bonding to antibonding interactions provide information about the overall bond character and strength and intramolecular CT [26,27]. Determining the order of individual bonds in terms of strength through quantitative analysis was difficult due to the significant number of conjugative and hyper conjugative interactions that strengthen or weaken some bonds. Thus, the hybrid character, the polarization of hybrid orbitals, and p character were used qualitatively to predict the bond strength. The oxygen atoms in nelarabine have the highest individual hybrid character and polarization coefficients in their O-H bonds, followed by nitrogen in N-H bonds, oxygen in C-O bonds, nitrogen in C-N bonds, and carbon in C-C bonds, indicating the importance of oxygen and nitrogen for bond formation. Among the carbon atoms bonded to either oxygen or nitrogen in nelarabine, the carbon atoms with the highest p character are C6 in O5-C6 (sp 2.51sp 4.37 ) and C21 in O20-C21 (sp 2.61 -sp 4.13 ), which suggests that both bonds are the weakest among the C-N and C-O bonds. In contrast, the carbon atoms with the lowest p character are C11 in C11-N12 (sp 1.86 -sp 1.88 ), C17 in C17-N18 (sp 1.86 -sp 1.90 ) C17 in N16-C17 (sp 1.88 -sp 1.89 ), C14 in C14-N18 (sp 1.89 -sp 1.90 ), and C15 in C15-N16 (sp 1.93 -sp 1.81 ). This suggests that the five bonds are the strongest among the C-N and C-O bonds, which parallels the findings of QTAIM analysis.

NLO properties.
Considering the conjugation and hyperconjugation exhibited by nelarabine, NLO analysis was performed to verify its feasibility for optoelectronic and photonic applications by studying the polarizabilities and hyperpolarizabilities. The total static dipole moment (μ), mean polarizability (α), anisotropy of polarizability (∆α), and mean first-order hyperpolarizability (β) of nelarabine were estimated. The x, y, and z components of μ, α, and β were used to extract the values of interest using the following equations [28][29][30]: The results of NLO analysis are summarized in Table 7 and compared with those of urea as a reference standard. Nelarabine exhibits moderate β values, which were 2.59 times higher than those of urea (μ = 1.3732 Debye, β = 0.3728 × 10-30 esu) [28]. The results confirm that nelarabine can be used in optoelectronic applications with low efficiency. However, this finding suggests that the optoelectronic applicability of nelarabine could be drastically improved with further modifications to the purine and sugar moieties that enhance the donoracceptor interactions between the moieties. The thermodynamic parameters, including zero-point vibrational energy, thermal energy, specific heat capacity, rotational constant, entropy, and dipole moment of nelarabine, were calculated at 298.15 K and 1 atm; the results are listed in Table 8. The calculated standard thermodynamic values can be used to calculate the changes in heat capacity, enthalpy, and entropy in a reaction.

Pharmacological investigation.
The applicability of molecules as potential drugs generally satisfies Lipinski's rule of five [31]. The physicochemical, lipophilicity, water solubility, and drug-likeness parameters of nelarabine were calculated using SwissADME; the results are summarized in Table 9. The bioavailability radar, which reflects the suitable physicochemical space for oral bioavailability, was calculated by SwissADME and illustrated in Figure 7. The pharmacokinetic profile parameters are based on absorption, distribution, metabolism, and excretion (ADME), which include human intestinal absorption (HIA), blood-brain barrier penetration (BBB), Pglycoprotein (P-gp) inhibitor and substrate, CYP1A2 inhibitor, CYP2C19 inhibitor, CYP2C9 inhibitor, CYP2D6 inhibitor, CYP2D6 substrate, CYP3A4 inhibitor, CYP3A4 substrate, skin permeability (LogKp), the permeability of Madin-Darby canine kidney cells (MDCK cells), plasma protein binding, and CaCO-2 cell permeability, were calculated using Pre-ADMET and SwissADME [32,33]; the results are summarized in Table 10. The sites of metabolism by cytochrome P450 were predicted by SOMP; the results are presented in Table 11 and Figure 8. The pharmacodynamic profile parameters, including pharmacological activities and adverse reactions, were calculated using PASSOnline; the results are listed in Tables S3-S4. In addition, the cancer cell line cytotoxicity, organ toxicity, and related side effects were calculated using CLC-Pred and MetaTox, respectively; the results are summarized in Tables 12-13.
The results in Table 9 indicate that nelarabine satisfies Lipinski's rule for drug-likeness, with an oral bioavailability of 55% and that it displays favorable physicochemical properties, including high water solubility and good acid-base character because it has more hydrogen bond acceptors (8) than donors (4). Nelarabine had an adequate lipophilicity (cLogP) value (−1.35) and a high topological polar surface area (TPSA) value (148.77 Å²), which indicates low cell permeability. Therefore, the bioavailability was considered limited, as illustrated in Figure 7, where nelarabine is not totally confined in the suitable physicochemical space for oral bioavailability.  The analysis of the pharmacokinetic profile of nelarabine presented in Table 10 reveals moderate HIA (20%-70%), no BBB penetration (less than 0.4), low MDCK (<25 nm/s), and moderate CaCO-2 (4-70 nm/s) cell permeability, which are attributed to the physicochemical properties and thereby affirming its low potential to become an oral drug. In addition, P-gp is overexpressed in cancer cells and is responsible for drug efflux in tumors. Nelarabine does not inhibit P-gp, indicative of limited bioavailability and anti-tumor activity [34]. Moreover, nelarabine exhibited weak plasma protein binding (<90%), suggesting swift exertion, strong pharmacological effects, and strong interactions with the targets. Nelarabine also exhibits a negative LogKp value, which corresponds to skin impermeability. Furthermore, the computed metabolism parameters indicate that nelarabine is a weak substrate of CYP3A4 while no inhibition was evident for all the listed cytochrome P450 members in the SwissADME results; However, inhibition of CYP3A4 was observed in the Pre-ADMET results. This suggests appropriate metabolism by the cytochrome P450 members and the possibility of drug-drug interactions with CYP3A4. Moreover, regarding the sites of metabolism by cytochrome P450, C9 (9) and C21 (25) were determined to be the main sites for O-phosphorylation by cytochrome P450 members (Table 11, Figure 8), in which nelarabine is converted to ara-GTP.    The pharmacodynamic profile of nelarabine presented in Tables 12-13 and S3-S4 (Supplementary Material) reveals many pharmacological activities, in addition to high antitumor activity, antiviral activity, carcinogenicity, mutagenicity, and severe adverse reactions. Among the most probable pharmacological activities were antiviral activities against poxvirus, herpes, and picornavirus (Table S3). In addition, nelarabine exhibits a high probability of cytostatic, antineoplastic, and antimetabolite activity through destructive interactions with DNA, which suggests anticancer, carcinogenic, mutagenic, and reproductive effects (Table 12). However, it exhibits selectivity for attacking tumor cells relative to non-tumor cells while displaying high anticancer activity against childhood T-cell acute lymphoblastic leukemia (CCRF-CEM), lung adenocarcinoma (PC-9), promyeloblast leukemia (HL-60), childhood acute myeloid leukemia with maturation (Kasumi 1), non-small cell lung carcinoma (NCI-H23), and non-small cell lung cancer stage 3 (NCI-H838). Anticancer activity against glioblastoma (SNB-7) is listed; however, due to poor BBB penetration, this activity should be ignored for nelarabine but not for ara-GTP [35] (Table 13). Analogous to almost all anticancer drugs, nelarabine displays possible severe adverse reactions (Table S4), which include sweating, diarrhea, inflammation, headache, nausea, pain, acidosis, hyperuricemia, splenomegaly, stomatitis, ototoxicity, agranulocytosis, thrombocytopenia, leukopenia, anemia, respiratory failure, coma, and several other probable adverse reactions. Pa, the probability to be active; Pi, the probability to be inactive Pa, the probability to be active; Pi, the probability to be inactive

Conclusions
Nelarabine was synthesized and modeled using DFT/TD-DFT calculations (B3LYP/6-31G* level of theory) and QSAR. The experimental and calculated IR spectral parameters were in excellent agreement. The experimental absorption spectrum in a 9:1 mixture of phosphate buffer (pH 7.0) and ethanol was in excellent agreement with the theoretical absorption spectrum calculated in ethanol. According to FMO analysis, nelarabine exhibited low reactivity and kinetic stability through a high EHOMO-ELUMO energy gap and low global hardness. Nelarabine demonstrated low efficiency in nonlinear optical activity according to NLO analysis. The NBO analysis conclusions paralleled the conclusions from QTAIM analysis regarding hydrogen bond stability, covalent bond stability, and the localization of intramolecular CT within the modified purine moiety. Natural charge and MEP map analyses agreed on the sites susceptible to electrophilic and nucleophilic attacks; however, they oppose the findings from QSAR models regarding the selectivity of metabolism by cytochrome P450 members. The physicochemical profile of nelarabine suggests inadequate oral bioavailability; however, because of its high solubility, intravenous administration, cytotoxicity, and antimetabolic properties, it has high potential as an anticancer and antiviral compound. According to QSAR models, Nelarabine exhibits poor BBB penetration and no P-gp inhibition, which corresponds to fewer adverse effects before being metabolized into ara-GTP-the most probable metabolic form through O-phosphorylation site predictions-which reportedly demonstrates improved bioavailability. The pharmacodynamic profile of nelarabine was investigated; however, to understand the complete profile, an extensive study with the most probable metabolites, including ara-GTP, must be conducted. The QSAR models aid in drug discovery but are not conclusive regarding the drug's effectiveness. Quantum chemical findings and the known potential of modified nucleosides regarding anticancer and antiviral activities promote further research into inexpensive synthetic modification routes to discover viable anticancer and antiviral candidates, including those wherein nelarabine is the main compound.

Funding
This research received no external funding.
However, the large-scale preparation of 3 by this method is not possible because of the difficulty in separating 3 from its α-anomer.
There are alternative methods for synthesizing 3, which are based on the transformation of natural and synthetic purine nucleosides. For example, the five-step transformation of commercially available arabinofuranosyladenine (araA; 4) through intermediates 5-8 results in the formation of 3 (Scheme S2) [36]. This approach for the preparation of 3 was feasible after developing the chemo-enzymatic araA synthesis route involving the use of enzymes such as nucleoside phosphorylases [37].
The introduction of a CH 3 O group at the C-6 position of the purine moiety is an important step in synthesizing 3. The most convenient method for introducing the CH3O group in the purine moiety is the nucleophilic displacement of chlorine in 2-amino-6-chloropurine by using sodium methylate. Guanosine (9), a natural nucleoside, is an effective starting compound for the convenient preparation of 2-amino-6-chloropurine derivatives by protectiondeprotection reactions and nucleophilic displacement, which are typically utilized in nucleoside chemistry (Scheme S3) [37]. Scheme S3. Synthesis of 3 from 9.
The deacetylation of 11 through treatment with hydroxylamine is an inconvenient step in the transformation of 9 to 3 because of its low selectivity, which results in the formation of a mixture of 2′-and 3′-deacetylated products. The subsequent treatment of 12 with trifluoromethanesulfonic anhydride and then with acetic acid gave an acetylated derivative (14). The deacetylation of 14 through treatment with a solution of ammonia or sodium methylate in methanol afforded 3.
An analogous approach for the preparation of 3 from 9 was achieved by the same team by using 3′,5′-silyl instead of acetyl protecting groups [38]. Because these approaches use inexpensive and available natural nucleosides such as 9, they are more advantageous for the preparation of 3. However, these approaches involve using expensive and toxic reagents, limiting their application for the large-scale synthesis of 3.
Another method for the transformation of 9 to 3 by using an 8-hydrazino derivative (15) as an intermediate (Scheme S4) has also been described [39]. Other arabinofuranoside derivatives of purines, such as fludarabine, were obtained by using the same approach.
Schemes S1-S4 show that the chemical synthesis of purine arabinosides involves multiple steps and requires toxic reagents. Progress in the preparation of such nucleosides has been achieved by using bacterial phosphorylase in transglycosylation reactions [40]. This approach has also been used to synthesize 3 [41]. Arabinofuranosyluracil (16), which can be obtained by chemical or enzymatic deamination from commercially available arabinofuranosylcytosine (Cytozar), was used as a sugar moiety donor in the synthesis of 3. Uridine phosphorylase transformed 16 to uracil (18) and arabinofuranosyl-1-phosphate (17) (Scheme S5). The second enzyme, purine nucleoside phosphorylase, catalyzes the glycosylation of 1 to obtain 3.

Scheme S5. Enzymatic synthesis of 3.
The substrate specificity of purine nucleoside phosphorylase depends on the structure of the purine heterocycle. Therefore, some transglycosylation reactions proceed slowly and require a long time to complete. In general, this method is universal and can be used to synthesize biologically active purine arabinosides such as fludarabine [41].
Using 17 as a sugar moiety donor instead of 16 in the transglycosylation reaction also gave 3, albeit in a low yield [6]. Furthermore, this strategy did not afford the desired product on a large scale.
The acetylation of 19 with acetic anhydride in acetonitrile in the presence of triethylamine and N,N-dimethylamine pyridine resulted in the formation of a triacetate derivative (20), which was isolated in the crystalline form with 90% yield. The treatment of 20 with a mixture of phosphor oxychloride, benzyltriethylammonium chloride, and N,Ndimethylaniline in acetonitrile at 100-110 °C, followed by a work-up, as described in the experimental section, gave a 6-chloro derivative (21). Compound 21, without further purification, was treated with a solution of potassium carbonate in methanol at 50-60 °C and then with Dowex 50Wx8 (H + -form, 200 mesh) to obtain deacetylated 6-chloro arabinoside (22) as an amorphous powder. To replace chlorine with a methoxy group, 22 was treated with a solution of sodium methylate in methanol, followed by neutralization with Dowex 50Wx8 (H +form, 200 mesh). The resulting 3 was purified by SiO2 column chromatography and recrystallized from water. The final yield of 3 was 43.8%.