Structural and Functional Characterization of 4-Hydroxyphenylacetate 3-Hydroxylase from Escherichia coli

The hydroxylation of phenols into polyphenols, which are valuable chemicals and pharmaceutical products, is a challenging reaction. The search for green synthetic processes has led to considering microorganisms and pure hydroxylases as catalysts for phenol hydroxylation. Herein, we report the structural and functional characterization of the flavin adenine dinucleotide (FAD)-dependent 4-hydroxyphenylacetate 3-monooxygenase from Escherichia coli, named HpaB. It is shown that this enzyme enjoys a relatively broad substrate specificity, which allows the conversion of a number of non-natural phenolic compounds, such as tyrosol, hydroxymandelic acid, coumaric acid, hydroxybenzoic acid and its methyl ester, and phenol, into the corresponding catechols. The reaction can be performed by using a simple chemical assay based on formate as the electron donor and the organometallic complex [Rh(bpy)Cp*(H₂O)]²⁺ (Cp*: 1,2,3,4,5-pentamethylcyclopentadiene, bpy: 2,2′-bipyridyl) as the catalyst for FAD reduction. The availability of a crystal structure of HpaB in complex with FAD at 1.8 Å resolution opens up the possibility of the rational tuning of the substrate specificity and activity of this interesting class of phenol hydroxylases.     

Construction of a Chimeric Biosynthetic Pathway for the De Novo Biosynthesis of Rosmarinic Acid in Escherichia coli

Hydroxycinnamic acid esters (HCEs) are widely‐distributed phenylpropanoid‐derived plant natural products. Rosmarinic acid (RA), the most well‐known HCE, shows promise as a treatment for cancer and neurological disorders. In contrast to extraction from plant material or plant cell culture, microbial production of HCEs could be a sustainable, controlled means of production. Through the overexpression of a six‐enzyme chimeric bacterial and plant pathway, we show the de novo biosynthesis of RA, and the related HCE isorinic acid (IA), in Escherichia coli. Probing the pathway through precursor supplementation showed several potential pathway bottlenecks. We demonstrated HCE biosynthesis using three plant rosmarinic acid synthase (RAS) orthologues, which exhibited different levels of HCE biosynthesis but produced the same ratio of IA to RA. This work serves as a proof‐of‐concept for a microbial production platform for HCEs by using a modular biosynthetic approach to access diverse natural and non‐natural HCEs.     

（R）-2-[4-甲氧基-3-（3-甲氧基丙氧基）苄基]-3-甲基丁酸的制备改进

本文以异香草醛为原料经过5步反应合成了Aliskiren的一个重要中间体——（R）-2-[4-甲氧基-3-（3-甲氧基丙氧基）苄基]-3-甲基丁酸。醚化中采用超声波反应,缩短了反应时间,提高了产率。所需手性中心由（R）-3-异戊酰基-4-苄基-2-噁唑烷酮诱导产生,针对去除诱导剂时需断裂环外酰胺键,通常会先引起分子中的酯键断裂,因而很难将诱导剂断裂下来,实验采用氢过氧化锂（LiOOH）高选择性地断裂环外酰胺键,实验还选用钙盐沉淀法纯化目标产物,均取得良好的效果。     

双菌氧化还原耦联转化外消旋2-辛醇制备(R)-2-辛醇

建立了一种新的制备手性2-辛醇的方法——双菌氧化还原耦联转化外消旋2-辛醇制备(R)-2-辛醇。通过筛选得到了一株选择性氧化外消旋2-辛醇中(S)-2-辛醇的菌株Candida cylindracea ATCC 14830,其产物的光学纯度e.e.>98%,(R)-2-辛醇的产率>46%。与报道的一株还原2-辛酮得到(R)-2-辛醇的菌株Oenococcus oeni CECT 4730氧化还原耦联,底物浓度可达40 g/L,产物的e.e.>98%,产率>92%。     

(1R, 2R)-反式环己烷二甲酸的合成工艺

以六氢苯酐为原料,采用顺反异构化反应合成反式-1,2-环己烷二甲酸;然后,选用较为廉价的R-(+)-α-甲基苄胺(R-PEA)作为拆分剂,通过手性拆分、酸化合成(1R,2R)-反式环己烷二甲酸。探讨了催化剂种类、反应温度和反应时间对产品顺反式比例的影响;同时考察了溶剂种类和用量对手性拆分效果的影响。反式-1,2-环己烷二甲酸的最优合成工艺条件为:硫酸为催化剂,反应温度120℃以上,反应时间12 h左右,在该反应条件下产品收率为80%;采用1HNMR测定了产物中反式质量分数为99.3%;最佳手性拆分条件为:甲醇作溶剂,n(反式-1,2-环己烷二甲酸)∶n(R-PEA)=1∶1,每10 g反式-1,2-环己烷二甲酸加入30 mL甲醇,在该反应条件下(1R,2R)-反式环己烷二甲酸·(R)-PEA盐的收率可达38%;经过酸化后得到(1R,2R)-反式环己烷二甲酸,酸化收率为85%;采用手性柱HPLC测定了目标产物的光学纯度(ee值)为98.48%。     

胡椒乙酸的简易合成

以胡椒醛为原料,经3步反应合成了胡椒乙酸。先由甲基甲硫基亚砜和胡椒醛反应得到2-(3′,4′-亚甲二氧基苯基)-1-(甲硫基)-1-(甲硫酰)乙烯,再在Cu2 催化下得到胡椒乙酸乙酯,然后对其进行柱纯化,NaOH皂化、盐酸酸化,得到目标化合物。用NMR表征了中间体和目标产物的结构,按胡椒醛计算总收率为57.0%,产品纯度98.6%(HPLC)。     

医药中间体(3R,4R)-3-[(1R)叔丁基二甲基硅氧乙基]-4-乙酰氧基-2-氮杂环丁酮的合成

以6-氨基青霉烷酸(6-APA)为原料经重氮化、溴化、酯化、还原、开环、氧化反应得到目标产物医药中间体(3R,4R)-3-[(1R)叔丁基二甲基硅氧乙基]-4-乙酰氧基-2-氮杂环丁酮。经1H NMR,IR证明得到了氮杂环丁酮,提高了酯化反应的收率,改变了格氏试剂反应中苛刻的条件,降低了开环反应的温度并提高了开环收率,总收率为35.88%。     

(R)-2,5-二氢-3,6-二甲氧基-2-异丙基吡嗪的合成

以D-缬氨酸为原料,经BOC基保护、酰胺化、环合和甲基化共4步合成得到目标化合物(R)-2,5-二氢-3,6-二甲氧基-2-异丙基吡嗪,总收率为44.1％,各步中间体及目标物结构经MS和1HNMR确证.改进后的方法简化了操作、降低了成本,适合于工业化生产.     

(-)-1R,2S,5R-8-(4-溴苯)薄荷醇的合成与表征

以R-( )-长叶薄荷酮为起始原料,经1,4-加成、还原、溴代、水解等4步反应合成了标题化合物,总产率77%。其结构用1HNMR、13CNMR和IR进行了表征。     

(1R,2S)-2-(3,4-二氟苯基)环丙胺的合成

替卡格雷是一种口服选择性小分子抗凝血药,不需要通过代谢激活,自身具有抗血小板活性。(1R,2S)-2-(3,4-二氟苯基)环丙胺是合成替卡格雷的一个关键中间体。该文在文献报道的合成路线基础上对其中关键步骤——不对称Corey-Chaykovsky环丙烷化反应进行了研究,筛选出最优反应条件:以L-薄荷醇为手性辅剂,三甲基碘化锍盐为硫叶立德试剂,二甲亚砜和四氢呋喃为混合溶剂,温度为10～12℃,质量分数10%的碘化亚铜为催化剂时,反应收率为60.5%;合成(1R,2S)-2-(3,4-二氟苯基)环丙胺5步总收率为20.0%。     

氯化(8S,9R)-(-)-N-苄基辛可尼定的合成

等摩尔的苄氯与辛可尼定在无水乙醇中回流2－4h,即可得到氯化（8S,9R）－（－）－N－苄基辛可尼定,产率为60％,e,e．值为＞99％。     

沃拉帕沙中间体手性氨基环己烯基丙烯酸的合成工艺改进

摘要：以(E)-3-(5-硝基-1-环己烯基)丙烯酸(Ⅱ)为原料,经酯化、硝基还原、拆分、缩合、水解等反应制备了(R,E)-3-(5-乙氧羰基氨基-1-环己烯基)丙烯酸(Ⅰ)。就Ⅰ合成的各歩反应条件进行了优化。其中,(R,E)-3-(5-氨基-1-环己烯基)丙烯酸乙酯的制备采用D-苹果酸作为拆分剂,甲醇:丙酮=1:1作为溶剂,收率为35.6%。改进后目标产物的总收率达到了27.4%。新合成路线操作简便,反应条件温和,使用的原料和试剂成本都比较低廉,适合工业化生产。目标化合物及中间体的结构经1HNMR、ESI-MS等确证。     

Investigation of poly(β-malic acid)synthesis pathways and regulation by strains of Aureobasidium pulluans

The possible biosynthesis pathways of poly(β-malic acid)(PMLA)and the feasible approaches to regulating PMLA production in A. pullulans BS24 were studied.To investigate the effects of the metabolic inhibitors of tricarboxylic acid cycle(TCA)cycle on PMLA fermentation,supplementation of the inhibitors to the medium was implemented.The results demonstrated that trifluoroacetic acid inhibited PMLA production,but malonic acid and maleic acid promoted PMLA production and isocitrate lyase activity.It could be concluded that PMLA synthesis was related to the TCA cycle and glyoxylate pathway in A. pullulans.Based on this result,the method of facilitating the accumulation of PMLA via metabolic intermediates was further designed.The medium containing 3.0 g·L^-1 fumaric acid or 1.5 g·L^-1 L-malic acid was used.Isocitrate lyase activity was increased by 18.39% and 25.30%,respectively.And the two added intermediates also increased the activity of L-malate dehydrogenase and fumarase,while reduced the activity of isocitrate dehydrogenase and α-ketoglutaric acid dehydrogenanse,and the final PMLA yield was increased by 46.58% and 43.70%,respectively.The metabolic intermediates could modify the redistribution of metabolic flux between TCA cycle and glyoxylate pathway,therefore,carbon source could be efficiently used to synthesize PMLA.     

Shifting the pH Optima of (R)-Selective Transaminases by Protein Engineering

Amine transaminases (ATAs) are powerful biocatalysts for the stereoselective synthesis of chiral amines. However, wild-type ATAs usually show pH optima at slightly alkaline values and exhibit low catalytic activity under physiological conditions. For efficient asymmetric synthesis ATAs are commonly used in combination with lactate dehydrogenase (LDH, optimal pH: 7.5) and glucose dehydrogenase (GDH, optimal pH: 7.75) to shift the equilibrium towards the synthesis of the target chiral amine and hence their pH optima should fit to each other. Based on a protein structure alignment, variants of (R)-selective transaminases were rationally designed, produced in E. coli, purified and subjected to biochemical characterization. This resulted in the discovery of the variant E49Q of the ATA from Aspergillus fumigatus, for which the pH optimum was successfully shifted from pH 8.5 to 7.5 and this variant furthermore had a two times higher specific activity than the wild-type protein at pH 7.5. A possible mechanism for this shift of the optimal pH is proposed. Asymmetric synthesis of (R)-1-phenylethylamine from acetophenone in combination with LDH and GDH confirmed that the variant E49Q shows superior performance at pH 7.5 compared to the wild-type enzyme.     

(2R, 3S)-3-羟基-天冬氨酸盐酸盐的合成研究

本文介绍了羟基天冬氨酸合成的,以D-酒石酸二乙酯为原料,与氯化亚砜反应成亚磺酸类化合物,再与叠氮化钠发生开环反应后,催化加氢还原后得到羟基天冬氨酸二乙酯,经皂化反应后得到目标产物,四步反应的总收率为42.04%。     

固定化沙雷氏菌脂肪酶拆分(R,S)-2-羟基-4-苯基丁酸乙酯

利用海藻酸钙-戊二醛交联法对本实验室筛选到的一株能选择性拆分(R,S)-2-羟基-4-苯基丁酸乙酯〔(R,S)-HPBE〕的沙雷氏菌脂肪酶进行固定化,并对固定化脂肪酶的酶活和拆分条件进行了研究。结果表明,最适反应温度为50℃,pH=7.0,底物浓度40 mmol/L,ρ(酶液)=200 g/L,在该条件下,反应10 h后,(R)-2-羟基-4-苯基丁酸乙酯〔(R)-HPBE〕产率达93.4%,光学纯度(e.e.)为96.2%。连续反应12批次,固定化脂肪酶仍可使(R)-HPBE产率维持在80%以上。     

新手性试剂(1R,2S)-2-氨基醇的合成

采用格氏试剂C6H13MgBr和C10H2MgBr对光学活性O-TMS保护的(R)-氰醇的氰基加成,随之用NaBH4对亚胺化合物立体诱导还原氢化,以98%的de值合成了两个新的手性试剂(1R,2S)-2-氨基醇,产率分别达到59%和62%.并通过X射线单晶结构分析法测定了分子结构和晶体结构.