This work reports efforts to improve the efficiency and green metrics associated with the chemical synthesis of single-tailed monorhamnolipids. Scaling of synthetic schemes for monorhamnolipids recently reported from this laboratory has been challenging, as large-scale production typically requires high-pressure equipment and an inert atmosphere due to the pyrophoric nature of a palladium/carbon (Pd/C) catalyst used for a key deprotection step. Furthermore, using Reformatsky condensation in conjunction with a methyl ester carboxylic acid protecting group, a safer, simpler, and “greener” synthetic pathway to 3-hydroxyalkanoic acid lipid tails is achieved. The two diastereomers of the resulting single-tail rhamnolipids from both 3-hydroxydecanoic acid and 3-hydroxytetradecanoic acid lipid chains are separated and independently characterized. Surface tensiometry was performed on these materials at pH 4 (acid neutral state) and 8 (acid anionic state). All rhamnolipids exhibit minimum surface tension values of 30–36 mN/m. Large differences in critical micelle concentration (CMC) values are observed between diastereomers for α-rhamnose 3-hydroxydecanoic acid at pH 4, with α-rhamnose (R)-3-hydroxydecanoic acid having a CMC of ∼380 μM compared to 1.7 mM for α-rhamnose (S)-3-hydroxydecanoic acid. For α-rhamnose 3-hydroxydecanoic acid diastereomers at pH 8, the CMC values differ slightly for the two diastereomers, with α-rhamnose (R)-3-hydroxydecanoic acid at 13 mM and α-rhamnose (R)-3-hydroxydecanoic acid at 21 mM. Similarly, CMC values of the two α-rhamnose 3-hydroxytetradecanoic acid diastereomers at pH 4 are similar at ∼100 μM but exhibit large differences at pH 8, with the racemic and α-rhamnose (R)-3-hydroxytetradecanoic acid with a CMC value of ∼500 μM and the α-rhamnose (S)-3-hydroxytetradecanoic acid exhibiting a CMC value of 1.8 mM.

中文翻译：

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单链鼠李糖脂化学合成的优化

这项工作报告了努力提高效率和绿色标准与单尾单鼠李糖脂的化学合成有关。该实验室最近报道的合成单鼠李糖脂的合成方案规模具有挑战性，因为大规模生产通常需要高压设备和惰性气氛，这是因为关键的钯/碳（Pd / C）催化剂具有自燃性质脱保护步骤。此外，结合使用Reformatsky缩合和甲酯羧酸保护基，可以实现更安全，更简单和“更绿色”的3-羟基链烷酸脂质尾部合成途径。从3-羟基癸酸和3-羟基十四烷酸脂质链得到的单尾鼠李糖脂的两个非对映异构体被分离并独立地表征。在pH 4（酸性中性状态）和8（酸性阴离子状态）下对这些材料进行表面张力测定。所有鼠李糖脂的最低表面张力值为30–36 mN / m。在pH为4的α-鼠李糖3-羟基癸酸与α-鼠李糖的非对映异构体之间观察到临界胶束浓度（CMC）值存在较大差异（R）-3-羟基癸酸的CMC为380μM，而α-鼠李糖（S）-3-羟基癸酸的1.7 mM 。对于pH为8的α-鼠李糖3-羟基癸酸非对映异构体，两种非对映体的CMC值略有不同，α-鼠李糖（R）-3-羟基癸酸为13 mM，α-鼠李糖（R）-3-羟基癸酸在21毫米 同样，两种α-鼠李糖3-羟基十四烷酸非对映异构体的CMC值在〜100μM时相似，但在pH 8时表现出很大差异，外消旋和α-鼠李糖（R）-3-羟基十四烷酸与CMC值约为500μM，α-鼠李糖（S）-3-羟基十四烷酸的CMC值为1.8 mM。