Isostructurality and the conformational role of the 2′,3′-moieties in the diversity of lamivudine crystal forms probed in halide salts
作者:Juan Carlos Tenorio Clavijo、Freddy Fernandes Guimarães、Javier Ellena、Felipe Terra Martins
DOI:10.1039/c4ce02373k
日期:——
Crystal engineering of the anti-HIV drug lamivudine has currently provided improvement in its pharmaceutical performance besides getting insights into several branches of nucleoside structural chemistry. Here, we demonstrated the synthon robustness and the role of the five-membered ring conformation in the diversity of lamivudine crystal forms even with supramolecular isomerism. Oxathiolane conformation defines the ability of lamivudine to assemble into different multicomponent molecular crystal forms. This was observed in a polymorph of lamivudine hydrochloride, which is related to the previously reported lamivudine hydrochloride monohydrate. The absence of water molecules has little effect on their supramolecular organization. If water is not present, just one conformational change from C3â²-endo puckering in the monohydrate form to the C2â²-endo one in the anhydrate form reported here is enough to cause a hydrogen bonding reorganization involving the 5â²-OH group. DFT calculations reveal a low energy gap for this change in the oxathiolane conformation. Therefore, lamivudine can variably forward its 5â²-OH group through changing oxathiolane conformations of similar energies. In addition, the isostructurality and robustness of the supramolecular synthons were illustrated in two halide salts of lamivudine with hydrobromic and hydrofluoric acids. While the previously reported lamivudine hydrochloride is strictly isostructural to the hydrobromide salt, the lamivudine hydrofluoride crystallized as a hydrofluoric acid cocrystal. HF cocrystallization appears to be primarily related to further stabilization between sheets rather than a major size effect.
目前,抗艾滋病病毒药物拉米夫定的晶体工程学不仅改善了其制药性能,还深入了解了核苷结构化学的多个分支。在这里,我们证明了五元环构象在拉米夫定晶体形态多样性(即使是超分子异构)中的协同稳健性和作用。氧硫杂环构象决定了拉米夫定组装成不同多组分分子晶体形式的能力。我们在盐酸拉米夫定的一种多晶型中观察到了这一点,这种多晶型与之前报道的盐酸拉米夫定一水合物有关。水分子的缺失对其超分子结构影响甚微。如果没有水,从一水合物中的 C3²-内侧皱褶到本研究中报告的无水物中的 C2²-内侧皱褶,只需一个构象变化就足以引起涉及 5²-OH基团的氢键重组。DFT 计算显示,氧硫杂环戊烷构象的这种变化具有较低的能隙。因此,拉米夫定可以通过改变能量相近的氧硫杂环戊烷构象,使其 5â²-OH基团向前移动。此外,在拉米夫定与氢溴酸和氢氟酸的两种卤化物盐中,超分子合子的同构性和稳健性也得到了说明。之前报道的盐酸拉米夫定与氢溴酸盐严格同构,而氢氟酸拉米夫定则结晶为氢氟酸共晶体。氢氟酸共晶似乎主要与薄片之间的进一步稳定有关,而不是主要的尺寸效应。