Institute of Pharmaceutical Science, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London, SE1 9NH, UK.
Pharm Res. 2012 Feb;29(2):511-24. doi: 10.1007/s11095-011-0575-6. Epub 2011 Sep 8.
Reports of the anomeric composition of amorphous lactose are rare and state a highly variable range of composition (between 0% and 60% w/w β content). We aimed to develop a quantitative measurement by (1)H-NMR of α and β anomer content in amorphous lactose produced by different production methods.
Amorphous lactose was prepared by spray and freeze drying 10% w/v aqueous solutions of lactose. NMR analysis was performed in DMSO; peak areas of partially resolved doublets at 6.3 and 6.6 ppm were used to calculate % of α and β lactose present. Polarimetery was used to determine optical rotation of lactose solutions.
Observed specific rotation for supplied crystalline alpha lactose monohydrate of 88° recorded in DMSO was constant for the length of a typical NMR experiment (max. 10 min). β/α anomer contents of amorphous lactose measured by (1)H-NMR had standard deviations as low as 0.1% w/w (n = 6). Drying a lactose solution 4 h after its preparation led to almost 35% w/w difference in anomer composition within solid amorphous material compared to samples dried after only 30 min, e.g. for freeze dried samples, β content was 60 ± 0.1% w/w (4 h) and 25 ± 1.0% w/w (30 min). Mutarotation leads to this increase in β anomer concentration in aqueous solution and within the solid amorphous lactose stored at 25°C. e.g. after 56 d storage the β content of freeze dried lactose (30 min solution) increased from 25±1.0% to 50±0.5% w/w.
A simple solution-based (1)H-NMR method for measurement of anomeric composition of lactose has been established. The solution β/α ratio at the time of drying is mirrored in the composition of the resulting solid amorphous material. In order to produce a consistent anomer composition within spray and freeze dried amorphous lactose, the standing time for the feed solution should be greater than 4 h, such that the most dynamic region of the mutarotation profile has been exceeded. If the amorphous material has been formed from a solution that has not been allowed to equilibrate for 4 h, the resulting solid will continue to undergo mutarotation if trace amounts of moisture are present, until the anomeric β/α ratio slowly approaches 1.7.
关于无定形乳糖的比旋度组成的报告很少，并且组成范围变化很大（0%至 60%w/wβ含量之间）。我们旨在通过（1）H-NMR 定量测量由不同生产方法生产的无定形乳糖的α和β差向异构体含量。
通过喷雾和冷冻干燥乳糖 10%w/v 水溶液制备无定形乳糖。在 DMSO 中进行 NMR 分析；使用部分分辨的双峰在 6.3 和 6.6 ppm 处的峰面积用于计算存在的α和β乳糖的百分比。偏振计用于测定乳糖溶液的旋光度。
在 DMSO 中记录的供应的结晶α乳糖一水合物的观察到的比旋度为 88°，在典型的 NMR 实验（最长 10 分钟）过程中保持不变。（1）H-NMR 测量的无定形乳糖的β/α差向异构体含量的标准偏差低至 0.1%w/w（n=6）。与仅干燥 30 分钟后的样品相比，在乳糖溶液制备后 4 小时干燥会导致固体无定形材料中的差向异构体组成差异近 35%w/w，例如对于冷冻干燥的样品，β 含量为 60±0.1%w/w（4 小时）和 25±1.0%w/w（30 分钟）。变旋作用导致在 25°C 下储存在水溶液中和储存的固体无定形乳糖中的β 差向异构体浓度增加。例如，在 56 天储存后，冷冻干燥乳糖（30 分钟溶液）的β 含量从 25±1.0%增加到 50±0.5%w/w。
已经建立了一种简单的基于溶液的（1）H-NMR 方法来测量乳糖的差向异构体组成。干燥时溶液的β/α 比反映了所得固体无定形材料的组成。为了在喷雾和冷冻干燥的无定形乳糖中产生一致的差向异构体组成，进料溶液的静置时间应大于 4 小时，以超过变旋曲线的最动态区域。如果无定形材料是由未平衡 4 小时的溶液形成的，则如果存在痕量水分，形成的固体将继续经历变旋作用，直到差向异构体β/α 比缓慢接近 1.7。
