The crystal and molecular structure of 6-mercaptopurine monohydrate

XRD, vibrational spectra and quantum chemical studies of an anticancer drug: 6-Mercaptopurine

The single crystal of the hydrated anticancer drug, 6-Mercaptopurine (6-MP), has been grown by slow evaporation technique under room temperature. The structure was determined by single crystal X-ray diffraction. The vibrational spectral analysis was carried out using Laser Raman and FT-IR spectroscopy in the range of 3300-100 and 4000-400 cm(-1). The single crystal X-ray studies shows that the crystal packing is dominated by N-H⋯O and O-H⋯N classical hydrogen bonds leading to a hydrogen bonded ensemble. This classical hydrogen bonds were further connected through O-H⋯S hydrogen bond to form two primary ring R4(4)(16) and R4(4)(12) motifs. These two primary ring motifs are interlinked with each other to build a ladder like structure. These ladders are connected through N-H⋯N hydrogen bond along c-axis of the unit cell through chain C(5) motifs. Further, the strength of the hydrogen bonds is studied through vibrational spectral measurements. The shifting of bands due to the intermolecular interactions was also analyzed in the solid crystalline state. Geometrical optimizations of the drug molecule were done by Density Functional Theory (DFT) using the B3LYP function and Hartree-Fock (HF) level with 6-311++G(d,p) basis set. The optimized molecular geometry and computed vibrational spectra are compared with experimental results which show significant agreement. The natural bond orbital (NBO) analysis was carried out to interpret hyperconjugative interaction and intramolecular charge transfer (ICT). The chemical hardness, electro-negativity and chemical potential of the molecule are carried out by HOMO-LUMO plot. In which, the frontier orbitals has lower band gap value indicating the possible pharmaceutical activity of the molecule.

Adsorption of 6-mercaptopurine and 6-mercaptopurine-ribosideon silver colloid: A pH-dependent surface-enhanced Raman spectroscopy and density functional theory study. II. 6-mercaptopurine-riboside

Surface-enhanced Raman spectroscopy (SERS) has been applied to characterize the interaction of 6-mercaptopurine-ribose (6MPR), an active drug used in chemotherapy of acute lymphoblastic leukemia, with a model biological substrate at therapeutic concentrations and as function of the pH value. Therefore, a detailed vibrational analysis of crystalline and solvated (6MPR) based on Density Functional Theory (DFT) calculations of the thion and thiol tautomers has been performed. 6MPR adopts the thion tautomeric form in the polycrystalline state. The SERS spectra of 6MPR and 6-mercaptopurine (6MP) recorded on silver colloid provided evidence that the ribose derivative shows different adsorption behavior compared with the free base. Under acidic conditions, the adsorption of 6MPR on the metal surface via the N7 and possibly S atoms was proposed to have a perpendicular orientation, while 6MP is probably adsorbed through the N9 and N3 atoms. Under basic conditions both molecules are adsorbed through the N1 and possibly S atoms, but 6MP has a more tilted orientation on the silver colloidal surface while 6MPR adopts a perpendicular orientation. The reorientation of the 6MPR molecule on the surface starts at pH 8 while in the case of 6MP the reorientation starts around pH 6. Under basic conditions, the presence of the anionic molecular species for both molecules is suggested. The deprotonation of 6MP is completed at pH 8 while the deprotonation of the riboside is finished at pH 10. For low drug concentrations under neutral conditions and for pH values 8 and 9, 6MPR interacts with the substrate through both N7 and N1 atoms, possibly forming two differently adsorbed species, while for 6MP only one species adsorbed via N1 was evidenced.

Study of azathioprine encapsulation into liposomes

The factors influencing the encapsulation of azathioprine (AZA) into liposomes were investigated to find out the conditions for its optimal entrapment. Similar studies for comparison were also carried out on 6-mercaptopurine (6-MP), of which AZA is a prodrug. AZA and also 6-MP show higher encapsulation efficiencies in MLVs as compared to LUVs. Variation in phospholipid composition does not seem to affect the loading capacity of either of the two drugs. The encapsulation efficiency of both the drugs improves upon addition of cholesterol in the bilayer, but the effect is seen only up to 30% cholesterol. Thereafter the effect becomes constant. AZA shows better incorporation in the positively charged liposomes as compared to those with neutral or negative charge. The entrapment of 6-MP is, however, found to be independent of the charge on the liposomes. Entrapment efficiency for both the drugs markedly depends on the pH of the hydration medium, yielding better entrapment efficiencies at high pH values. The rise in solute concentration initially causes increase in the entrapment of the two drugs which is followed by a decreasing phase.

Structure of rubredoxin from Desulfovibrio vulgaris at 1.5 A resolution

The X-ray model of rubredoxin from Desulfovibrio vulgaris has been refined against 1.5 A X-ray diffraction data collected on a diffractometer. The final model comprises 395 non-hydrogen protein atoms, and 180 solvent O atoms. The final R-value for the model with calculated H atom positions included as fixed contributions is 0.098 over all reflections greater than 2 sigma I from infinity to 1.5 A. The error in co-ordinates is estimated to be 0.08 A. The solvent model was twice redetermined during the later stages of refinement and was instrumental in its success. One sequence error has been detected and corrected (Thr21----Asp). The iron-sulfur site bond angles are distorted from true tetrahedral symmetry, as found in other rubredoxin structures. A significant deviation from tetrahedral angles is seen at C alpha atoms 9, 10, 42 and 43, interior angles of the loops binding the iron atom. The planes of two aromatic groups, Tyr4 and Trp37, are nearly parallel to, and lie under, an extended system of atoms that includes the peptide bonds preceding the first cysteine residue of each cysteine loop as well as the cysteine side-chain, the iron, and the cysteine side-chain of the opposite loop, forming a previously unrecognized extended system that may function in electron transfer.

Synthesis and evaluation of acyclic sugar nucleosides

Acylated aldose dialkyl dithioacetals with bromine undergo replacement of one alkylthio group by bromine. These unstable bromides react, as by fusion with 2,4-bis(trimethylsilyloxy)pyrimidine, to give acylated 1-(pyrimidin-1-yl) derivatives that upon saponification afford acyclic sugar nucleoside analogues, some as separable mixtures of 1-epimers. Systemic stereochemical variants have been conducted. Pmr conformational studies show that the sugar chain is extended in certain examples, whereas others favor folded ("sickle") conformations, in line with a general rationale developed for acyclic-sugar derivatives. Condensation of the bromides with purines gives 9-substituted acyclic-sugar nucleoside analogues; synthesized systematically for various series, these include the D-pentoses in combination with 6-mercaptopurine. In vitro and in vivo biological activities vary according to stereochemistry of the sugar. The position of substitution of the sugar chain, the chirality at C-1', and the tautomeric form of the heterocycle, were established by x-ray crystallography of the product from D-arabinose and 6-mercaptopurine. The x-ray data permit correlation of C-1 chirality throughout the series and pmr data indicate the favored conformations.

Crystal structures of azathioprine dihydrate and 6-methylmercaptopurine trihydrate

The crystal and molecular structures of 6-methylmercaptopurine trihydrate and of azathioprine dihydrate were determined by the use of three-dimensional, X-ray, diffractometer data and were refined by least squares. Both molecules crystallize in the N(9)-H tautomer form, in contrast to the N(7)-H tautomer form found in crystals of 6-mercaptopurine. Unlike 6-mercaptopurine, or other thiopurines that have unsubstituted thio groups, the sulfur atoms of 6-methylmercaptopurine and azathioprine do not act as hydrogen-bond acceptors in the crystal structures. These two derivatives of 6-mercaptopurine assume a conformation in which the substituents on the sulfur atom are directed away from the imidazole moiety of the purine.