酶促合成肽的研究——Ⅰ.亮-脑啡肽色氨酸类似物的酶促合成

在先后以α-胰凝乳蛋白酶和木瓜酶作催化剂的作用下,从C端的LeuNH_2的氨基开始,逐个与N保护的氨基酸或其衍生物缩合,合成了亮-脑啡肽色氨酸类似物—TyrGlyGly Trp LeuNH_2~(**)。对酶的专一性、有机溶剂的选择和合成条件等进行了研究,在Z-TyrOMe和GlyGlyTrp LeuNH_2的缩合反应中,比较了相转移法和均相法。上述两种酶的酶促接肽的供体以N-酰基氨基酸酯为好,比相应的游离酸反应速度快,副反应少。如用嗜热菌蛋白酶,则以N-酰基氨基酸为好。酶促合成与从有机合成所得的产物相同。初步的体外实验表明合成的TyrGlyGlyTrpLeuNH_2和天然的亮-脑啡肽对豚鼠回肠的收缩显示相同程度的鸦片样的抑制作用。     

肽的酶促合成及其反应机制

先后以α-胰凝乳蛋白酶和木爪酶作催化剂以逐级缩合方式合成了[色]⁴亮-脑啡肽酰酶(TyGlyGlyTrpLeuNH₂),在合成中,对酶的专一性,有机溶剂的选择和合成条件等进行试探,比较了固相酶促法和液相酶促法,α-胰凝乳蛋白酶和木爪酶连接肽键中,以N-酰基氨基酸酯作为供体比相应的游离酸好,如用嗜热菌蛋白酶只能以N-酰基氨基酸为羧基组份,初步的体外实验说明合成的[色]⁴-亮脑啡肽酰酶与天然亮-脑啡肽有类似的鸦片样生理活性。     

酶促合成肽的研究 II: 含羧基侧链氨基酸的肽的酶促合成

用嗜热菌酶酶促合成了一系列含门冬氨酸、谷氨酸的肽. 实验证明, 缩合反应中羧基组份中的门冬氨酸β-羧基或谷氨酸γ-羧基毋需保护. 同时也研究了邻近氨基酸残基对缩合反应的影响.     

酶促合成肽的研究 Ⅱ.含羧基侧链氨基酸的肽的酶促合成

用嗜热菌酶酶促合成了一系列含门冬氨酸、谷氨酸的肽。实验证明,缩合反应中羧基组份中的门冬氨酸β-羧基或谷氨酸γ-羧基毋需保护。同时也研究了邻近氨基酸残基对缩合反应的影响。     

以N-保护消旋氨基酸为羧基组分的酶促合成肽的研究

用不同的氨基保护的消旋氨基酸或酯作为羧基组分,在α-胰凝乳蛋白酶或木瓜蛋白酶的催化下与另一氨基酸的酰胺或酯缩合形成预期的光活性肽产物。以L-构型底物计算肽的产率为55%～83%,化合物的物理学常数与用相应的N-保护-L-氨基酸或酯为羧基组分,分别用化学法或酶促法测定所得结果一致。研究结果表明:利用酶的立体专一性,在形成肽键的过程中进行立体选择可得到光学活性的产物而不需预先拆分;只要溶剂体系中含有酶所需要的微量必需水,酶促反应在有机溶剂中可以顺利地进行。     

酶促还原法合成(S)-Phoracantholide Ⅰ

1976年Brown小组[1]首次从按树天牛后胸腺体中分离得到其防御信息素,并鉴定其主要组分结构为9-癸内酯(又称Phoracantholide Ⅰ),1983年Mori小组[2]成功合成出Phoracantholide Ⅰ的两种对映异构体,并经过手性固定相气相色谱确定出天然Phoracantholide Ⅰ的构型应为R构型.其后有关Phoracantholide Ⅰ的手性合成屡见不鲜,其主要合成方法为:不对称反应法[3～5]、酯促还原法[6,7]等,这些方法各有特色.由其逆合成可知,此类化合物可由羟基羧酸内酯化合成得到,故本文用1-苯磺酰基丙酮为原料经两步合成出9-羟基癸酸,然后借鉴Naoshima等的工作经海藻酸钙固定化的面包酵母(Saccharomyces Cerevisiae)进行酶促还原引入手性中心,进而经内酯化反应合成出目标产物(S)-Phora-cantholide Ⅰ.合成路线如下:     

肽键的酶促合成

所谓肽键的酶促合成,实际上是指利用蛋白水解酶的逆转反应或转肽反应来进行的肽键合成。近年来,本方法有了某些新发展。它作为多肽化学合成的一个辅助和补充的方法,已经成功地用于许多小肽以及像脑啡肽和增血压素等生物活性肽的合成,更成功地是用于某些蛋白质如胰岛素、胰蛋白酶抑制剂,牛胰核糖核酸酶A、葡萄球菌核酸酶和细胞色素C等的结构与功能关系的研究。本文就最近研究概况作一简单介绍。     

亮-脑啡肽基因的合成

本文报道亮-脑啡肤基因的另一个合成途径。合成的基因,26个碱基对,是按照亮-脑啡肽的氨基酸顺序设计的。为了能够插入pBR 322质粒,基因带有EcoRI和BamHI限制性内切酶的单链粘性末端。化学合成的4个片段,8、9、17及18核苷酸,采用改良的三酯法。这些片段都具有正确的结构,最后在T_4-DNA连接酶的作用下,一步装配成脑啡肽基因。产物用聚丙烯酰胺凝胶电泳纯化,具有正确的连接点。     

离子液体中酶促区域选择性合成CFAE

碳水化合物脂肪酸酯(CFAE)作为一类非离子型生物表面活性剂,被广泛用于食品、医药及化妆品工业,一些CFAE还具有抗菌、抗肿瘤等特殊生物活性。非水介质中酶促区域选择性合成CFAE反应的瓶颈在于高极性碳水化合物与酰基供体不易相溶,并具有多个可酰化羟基。传统有机溶剂虽能提高极性底物在体系中溶解度,但常使酶活下降。新型绿色介质离子液体用于CFAE的酶法合成过程具有诸多优点,不仅生物催化剂能维持较好的活性与稳定性,且良好的底物溶解性可改善反应区域选择性及转化速率,反应体系还可重复利用。本文介绍了离子液体中影响酶促区域选择性合成CFAE反应的主要因素,包括酶、底物在离子液体中的溶解性能及底物自身性质等,详述了离子液体中酶促制备CFAE的研究进展,也指出了酶促合成CFAE存在的问题与发展前景。     

非水介质中曲克芦丁乙烯酯的酶促合成

在非水介质中,选择性催化曲克芦丁羟乙基上的伯羟基发生酯交换反应,合成一系列曲克芦丁乙烯酯.同时考察了酶源、酶量、反应介质、酰化试剂链长、溶剂含水量、反应时间等因素对曲克芦丁酶促酯交换反应区域选择性的影响.结果表明:以吡啶为溶剂,其含水量1%时,枯草杆菌碱性蛋白酶催化活性最高,随着酰基供体碳链的减少,产率增大,且反应达平衡的时间缩短.     

Asymmetric synthesis of cyclobutanones: synthesis of cyclobut-G

A simple, efficient, and stereoselective approach has been developed for obtaining chiral cis- and trans-disubstituted cyclobutanones from readily available alkyl- and functionalized alkyl-substituted enol ethers. The usefulness of these cyclobutanones is illustrated by an enantioselective synthesis of cyclobut-G (Lobucavir).     

Benzothiazines in synthesis. Formal synthesis of erogorgiaene

A benzothiazine, readily available in enantiomerically pure form via a completely selective, intramolecular addition of a sulfoximine-stabilized carbanion to an α,β-unsaturated ester, could be converted to a precursor to erogorgiaene in good overall yield.     

Total synthesis of apoptolidin: completion of the synthesis and analogue synthesis and evaluation

The total synthesis of apoptolidin (1) is reported together with the design, synthesis, and biological evaluation of a number of analogues. The assembly of key fragments 6 and 7 to vinyl iodide 3 via dithiane coupling technology was supplemented by a second generation route to this advanced intermediate involving a Horner-Wadsworth-Emmons coupling of fragments 22 and 25. The final stages of the synthesis featured a Stille coupling between vinyl iodide 3 and vinylstannane 2, a Yamaguchi lactonization, a number of glycosidations, and final deprotection. The developed synthetic technology was applied to the construction of several analogues including 74, 75, and 77 which exhibit significant bioactivity against tumor cells.     

金属蒸气合成在金属有机合成中的应用

本文简要地介绍了金属蒸气合成法的基本原理、仪器和实验技术, 并按金属原子分别与炔、单烯、多烯、环烯、芳烃体系、卤代烃、有机混和物的反应及有机金属硼化合物的合成, 对金属蒸气合成法在金属有机合成中的应用进行了讨论。     

Formal synthesis of nitidine through palladium-catalyzed isocoumarin synthesis

The isoquinolone intermediate 9 for the synthesis of nitidine was synthesized through palladium-catalyzed formation of isocoumarin 7 from o-styrylbenzoic acid derivative 5, which was prepared from palladium-catalyzed coupling reactions of aryl iodide 1 and 2 with vinylsilane.     

Studies towards the total synthesis of Sch 56036; isoquinolinone synthesis and the synthesis of phenanthrenes

The isoquinolinone hemisphere of Sch 56036 has been prepared using a modified Pomeranz-Fritsch reaction and the synthesis of the phenanthrene core has been modelled via a Suzuki coupling and subsequent ring closing metathesis.     

Tellurium in organic synthesis: synthesis of bioactive butenolides

Reduction of (Z)-β-butyltelluro-enones gives the corresponding γ-hydroxy vinylic tellurides with retention of the double bond configuration. Reaction of γ-hydroxy vinylic tellurides with 2 equiv of n-butyllithium produces 1,4-C,O-dianions, which on reaction with carbon dioxide give the corresponding butenolides.     

Radical-mediated synthesis of 3,4-dihydroisocoumarins: total synthesis of hydrangenol

A radically promoted synthesis of 3,4-dihydroisocoumarins has been achieved in moderate to good yields using titanocene(III) chloride (Cp₂TiCl) as the radical initiator. The total synthesis of (±)-hydrangenol has been completed using this radical technology. Cp₂TiCl was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and Zn-dust in THF under argon.     

Benzothiazines in synthesis. A total synthesis of pseudopteroxazole

An enantioselective total synthesis of the naturally occurring antitubercular agent pseudopteroxazole is described. The synthesis is organized around the use of a stereoselective, intramolecular addition of a sulfoximine carbanion to an alpha,beta-unsaturated ester to form an enantiomerically pure benzothiazine. Other important processes include a completely stereoselective intramolecular Friedel-Crafts alkylation and a stereoselective and regioselective hydrogenation. [structure: see text]     

Benzothiazines in synthesis. Toward the synthesis of pseudopteroxazole

[reaction: see text] The tricyclic benzothiazine 15 was prepared in a straightforward fashion via a completely stereoselective intramolecular Friedel-Crafts alkylation. This compound represents a potential precursor to the antitubercular agent, pseudopteroxazole. Its synthesis proceeded via a completely selective, intramolecular addition of a sulfoximine-stabilized carbanion to an alpha,beta-unsaturated ester, followed by functional group manipulations.