杜松烷型倍半萜天然产物的研究进展

http://dx.doi.org/10.13345/j.cjb.210165
中国科学院微生物研究所、中国微生物学会主办

文章信息

姜龙瑜, 温艳华, 彭雨, 陈天娇, 陈晶晶, 杨金玲, 巩婷, 朱平

Jiang Longyu, Wen Yanhua, Peng Yu, Chen Tianjiao, Chen Jingjing, Yang Jinling, Gong Ting, Zhu Ping

杜松烷型倍半萜天然产物的研究进展

Advances in biosynthesis of cadinane sesquiterpenes

生物工程学报, 2021, 37(6): 1952-1967

Chinese Journal of Biotechnology, 2021, 37(6): 1952-1967

10.13345/j.cjb.210165

文章历史

Received: February 25, 2021

Accepted: March 27, 2021

Abstract

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引用本文

姜龙瑜, 温艳华, 彭雨, 等. 杜松烷型倍半萜天然产物的研究进展. 生物工程学报, 2021, 37(6): 1952-1967

Jiang LY, Wen YH, Peng Y, et al. Advances in biosynthesis of cadinane sesquiterpenes. Chinese Journal of Biotechnology, 2021, 37(6): 1952-1967.

杜松烷型倍半萜天然产物的研究进展

姜龙瑜 , 温艳华 , 彭雨 , 陈天娇 , 陈晶晶 , 杨金玲 , 巩婷 , 朱平

中国医学科学院北京协和医学院药物研究所天然药物活性物质与功能国家重点实验室 & 国家卫生健康委员会天然药物生物合成重点实验室，北京 100050

收稿日期：2021-02-25；接收日期：2021-03-27

基金项目：重大新药创制科技重大专项平台建设(No. 2018ZX09711001-008-001)，中国医学科学院医学与健康科技创新工程协同创新项目(No. CIFMS-2017-I2M-4-004)，清华211-合成生物学学科建设(No. 201920100801) 资助

作者简介：巩婷中国医学科学院药物研究所副研究员、硕士生导师。研究方向为微生物活性天然产物的发现、天然药物的生物合成及生物催化。先后主持国家自然科学基金及教育部新教师基金等项目，并作为科研骨干参与多项国家级科研项目的工作。目前在国内外学术期刊上累计发表学术论文50余篇，参与编写专著4部;
朱平中国医学科学院药物研究所研究员、博士生导师、生物合成室主任，兼任国家卫生健康委天然药物生物合成重点实验室主任，天然药物活性物质与功能国家重点实验室副主任，中国菌物学会副理事长，中国中药协会药用菌物专业委员会主任委员，《菌物学报》《药学学报》等杂志编委。先后承担多项国家级科研项目，在国内外期刊上累计发表学术论文100余篇，累计授权8项中国专利和9项国际专利，参编5部著作，获得2011年度中国药学会科学技术三等奖1项.

摘要：杜松烷型倍半萜是一类双环倍半萜，立体化学复杂，具有广泛药理活性，如抗菌、抗炎、降糖等。迄今为止，已从多种植物和微生物中分离鉴定出具有不同结构及生物活性的杜松烷型化合物，相关杜松烷型倍半萜合酶的研究也取得较大进展。本文按5种结构类型对近4年(2017–2020年) 文献发表的结构新颖的124个杜松烷型化合物进行整理，并对其药理活性进行归纳总结，同时介绍了代表性杜松烷型化合物生物合成途径的解析概况，归纳了该类天然产物生物合成过程中关键杜松烷型倍半萜合酶的研究进展，并讨论了该类天然产物的研究前景和目前面临的一些问题。

关键词：杜松烷型倍半萜结构类型药理活性生物合成倍半萜合酶

Advances in biosynthesis of cadinane sesquiterpenes

Longyu Jiang , Yanhua Wen , Yu Peng , Tianjiao Chen , Jingjing Chen , Jinling Yang , Ting Gong , Ping Zhu

State Key Laboratory of Bioactive Substance and Function of Natural Medicines & Key Laboratory of Biosynthesis of Natural Products of the National Health Commission, Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100050, China

Received: February 25, 2021; Accepted: March 27, 2021

Supported by: National Mega-project for Innovative Drugs (No. 2018ZX09711001-008-001), CAMS Innovation Fund for Medical Sciences (No. CIFMS-2017-I2M-4-004), Disciplines Construction Project of Synthetic Biology (No. 201920100801)

Corresponding author: Ting Gong. Tel: +86-10-63165199; Fax: +86-10-63165197; E-mail: gongting@imm.ac.cn;
Ping Zhu. Tel: +86-10-63165197; Fax: +86-10-63037757; E-mail: zhuping@imm.ac.cn.

Abstract: Cadinanes are a class of bicyclic sesquiterpenes with complex stereochemistry and broad pharmacological activities, such as antibacterial, anti-inflammatory, and hypoglycemic activities. To date, structurally diverse and bioactive cadinane sesquiterpenes have been isolated and identified from a variety of plants and microorganisms. Moreover, deeper understandings on cadinane sesquiterpene synthases have been made. This article categorized the 124 new cadinanes which were published in the literatures in the past four years (2017–2020) into five structural types, and presented their pharmacological activities. We also illustrated the elucidation of the biosynthetic pathways for typical cadinanes, summarized the research progress on cadinane sesquiterpene synthases. Finally, current challenges and future prospects were proposed and discussed.

Keywords: cadinane sesquiterpenes structure type pharmacological activities biosynthesis sesquiterpene synthase

杜松烷型倍半萜属于双环倍半萜，基本骨架如图 1所示，是由法尼基焦磷酸(Farnesyl diphosphate，FPP) 为前体，经倍半萜合酶(Sesquiterpene synthase，STS) 催化而产生。基本骨架再经过一系列后修饰酶(氧化还原酶等) 的作用，形成结构复杂多样的产物^[1]。同时，该类天然产物具有广泛的药理活性，如抗菌^[2]、抗炎^[3]、降糖^[4]以及抗肿瘤^[5]等。抗疟药物青蒿素(Artemisinin) 和避孕药棉酚(Gossypol) 等均属于分离自植物中的该类产物，对于它们的研究工作自发现至今从未间断，研究领域也在逐渐拓宽^[6-9]。

图 1 杜松烷型倍半萜类天然产物生物合成途径示意图 Fig. 1 Schematic diagram of biosynthetic pathway of cadinane sesquiterpenes.

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经文献调研，仅针对杜松烷型倍半萜类天然产物的综述并不多见，Braulio M. Fraga在1985年到2013年间，先后发表了30篇涵盖杜松烷型倍半萜天然产物的分离提取、结构鉴定、化学合成及微生物转化的综述^[10-39]。Tian等^[40]在2016年对木棉植物中检测到的杜松烷型化合物及其生物合成途径进行了综述。本文则对近4年(2017–2020年) 来获得的结构新颖的杜松烷型倍半萜天然产物的化学结构(124个化合物) 及药理活性进行归纳，旨在为后续该类产物的基础研究及应用开发奠定基础。同时，介绍了两个代表性杜松烷型化合物(青蒿素和棉酚) 生物合成途径解析的概况。最后重点对不同构型的杜松烷型倍半萜骨架合成酶的研究现状进行总结，可为该类产物的生物合成研究提供思路及方向。

1 杜松烷型倍半萜类化合物新结构

从近4年的文献分析，已发表的杜松烷型化合物主要来源于植物(83/124)，少数来源于真菌(32/124) 和细菌(5/124)，还有极少数来源于动物(4/124)，见表 1。本文根据化合物取代基以及氧化还原程度的不同，将结构分为5大类，分别为：简单杜松醇类、芳环杜松烷类、杜松烷内酯/内酰胺类、杜松醛酮酸类以及复杂杜松烷衍生物。该部分将对化合物的结构特点及来源进行详细介绍。

表 1 杜松烷型化合物的来源 Table 1 Sources of cadinane compounds

Compounds	Origin	Reference
1	Microporus affinis HFG829	[41]
2–8	Ganoderma capense	[42]
9	Mikanian micrantha	[43]
10	Porphyra yezoensis	[44]
11–12	Trichaptum pargamenum	[45]
13–15	Chamaecyparis obtusa	[46]
16–18	Montagnula donacina	[47]
19–20	Trichoderma asperellum A-YMD-9-2	[48]
21–22	Paecilomyces sp. TE-540	[49]
23–25	Streptomyces sp.	[50]
26–28	Trichoderma virens QA-8	[51]
29	Anthemis nobilis	[52]
30–32	Croton dichogamus	[53]
33	Curcuma wenyujin	[4]
34	Resina commiphora	[54]
35–43	Heterotheca inuloides	[55]
44–45	Heterotheca inuloides	[56]
46–51	Alangium alpinum	[57]
52–57	Santalum album	[58]
58–60	Trichoderma sp. SM16	[59]
61	Trichoderma virens RR-dl-6-8	[60]
62–65	Mikanian micrantha	[43]
66	Curcuma wenyujin	[4]
67–70	Resina commiphora	[54]
71	Resina commiphora	[5]
72–73	Alangium alpinum	[57]
74–77	Commiphora myrrha	[61]
78–79	Trichoderma virens RR-dl-6-8	[60]
80	Kadsura heteroclita	[62]
81–83	Trichoderma virens QA-8	[51]
84–87	Puldidielultulula, Phyllidia coelestis, Acanthella cavernosa	[63]
88	Ganoderma capense	[42]
89–91	Heterotheca inuloides	[55]
92	Chamaecyparis obtusa	[46]
93–94	Leptosphaerulina chartarum sp. 3608	[64]
95	Panus conchatus	[65]
96	Trichoderma virens Y13-3	[66]
97–98	Artemisia annua	[3]
99	Chloranthus anhuiensis	[67]
100	Curcuma longa	[68]
101	Commiphora myrrha	[61]
102–104	Trichoderma sp. SM16	[59]
105–109	Trichoderma virens RR-dl-6-8	[60]
110	Abelmoschus sagittifolius	[69]
111	Tinospora sinensis	[70]
112–116	Cornus officinalis	[71]
117	Torilis japonica	[72]
118	Cleistochlamys kirkii	[73]
119–120	Eucalyptus robusta	[2]
121–123	Artemisia annua	[3]
124	Heterotheca inuloides	[55]

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1.1 简单杜松醇类

该类结构的骨架大多为反式并环、2, 3-位双键取代。通常在C-7位发生羟基取代，陆续有C-6、C-10、C-15等位羟基取代的报道，且少数羟基还会发生酰化(15)。因各位置羟基取代构型的不同，形成了结构多样的杜松醇同分异构体。近4年来，研究人员从多种植物的挥发油、微生物培养物以及海洋大型藻类中分离得到了25个该类化合物(1–25)，见图 2。

图 2 简单杜松醇类化合物结构(1–25) Fig. 2 Structures of simple cadinols (1–25).

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1.2 芳环杜松烷类

芳环杜松烷类化合物是近年来报道的新杜松烷型化合物中数量最多的一类，多在杜松烷碳骨架发生还原反应，两环均被还原至苯环较多见，A环被还原的化合物多于B环被还原的化合物。近4年来，研究人员主要从菊科(Compositae)、木兰科(Magnoliaceae) 等多种植物中分离鉴定36个该类化合物(26–61)，见图 3。

图 3 骨架高度还原的新型杜松烷化合物结构 (26–61) Fig. 3 Structures of novel aromatic cadinanes with highly reduced skeleton (26 – 61).

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1.3 杜松烷内酯/内酰胺类

杜松烷内酯/内酰胺类新化合物的异丙基侧链末位甲基氧化为羧基后，多与邻位的羟基或氨基形成五元不饱和内酯环或内酰胺环，少数内酯环被还原、脱水形成呋喃环。其中，从高山八角枫Alangium alpinum中分离得到的thespesilactam (72) 和alangiulactam (73) 结构较特殊，14位甲基氧化为羧基后，与C-5位氨基形成内酰胺环。近年来从没药树脂Resina Commiphor、甘菊Mikania micrantha、温郁金Curcuma wenyujin等多种植物以及真菌Trichoderma virens RR-dl-6-8中分离鉴定了18个该类化合物(62–79)。见图 4。

图 4 杜松烷内酯/内酰胺类化合物结构 (62–79) Fig. 4 Structures of cadinane lactones/lactams (62–79).

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1.4 杜松醛酮酸类

杜松醛酮酸类化合物的骨架大多数含有α, β-不饱和酮片段，部分末端甲基氧化为醛基、羰基或羧基等(80–109)。其中，从青蒿Artemisia annua L.中分离得到的arteannoide D (97) 和arteannoide E (98) 发生氧化重排反应而形成新颖的[5.6]结构。有些化合物中还含有异氰基等基团，对化合物活性产生一定的影响。另外，有极少数化合物如phacadinane E (99)、curcumane C (100) 等甲基发生氧化后A环发生断裂，从而形成一种不寻常的杜松烷骨架，见图 5。

图 5 杜松醛酮酸类化合物结构 (80–109) Fig. 5 Structures of cadinane aldehyde ketone acids (80–109).

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1.5 复杂杜松烷衍生物

复杂杜松烷衍生物包括杜松醇倍半萜氧苷(110–117)、杜松烷型倍半萜二聚体(123–124) 及杜松烷与间苯三酚等芳香族片段形成的异二聚体(118–122)。其中化合物arteannoide A (123) 是一种罕见的杜松烷型倍半萜二聚体，具有6, 8-二氧杂环[3.2.1]辛烷-7-一环体系。近4年来从菊科(Compositae)、木兰科(Magnoliaceae) 等多种植物中分离得到了15个该类化合物(110–124)，见图 6。

图 6 复杂杜松烷衍生物结构 (110–124) Fig. 6 Structures of complex cadinane derivatives (110–124).

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2 杜松烷型化合物药理活性 2.1 抗菌活性

杜松烷型倍半萜类化合物具有较强的抗菌活性，例如存在于多种植物精油中的α-cadinol对桦褶孔菌狭褶变种Lenzites betulina、变色栓菌Trametes versicolor和硫磺菌Laetiporus sulphureus的总平均抑菌浓度为0.10 mmol/L^[74]。Chang等研究了杜松醇骨架结构的并环方式、C-7位羟基的构型与抗菌活性的关系。其中，双环并环方式对抗菌活性影响最大，α-cadinol和τ-cadinol为反式并环，可完全抑制真菌的菌丝生长。τ-muurolol为顺式并环，抗菌活性则降低^[75]。化合物trichocadinins B-G (26-27、81-83、28) 均对尖孢镰刀菌Fusarium oxysporum f. sp. cucumebrium具有抗菌活性，最低抑菌浓度(MIC) 在1-64 μg/mL范围内。其中化合物trichocadinins B-D (26、27、81) 具有广谱的抗菌活性，trichocadinins B (26) 在C-13处缺乏醇功能基，抗菌活性强于trichocadinins C (27)。含有苯并呋喃部分的trichocadinins B (26) 和C (27) 与trichocadinins D-G (81-83、28) 相比抗菌活性更强^[51]；化合物7-hydroxy-3, 4-dihydrocadalene (44) 和7-hydroxy-cadalene (45) 具有较强的抗幽门螺杆菌活性，MIC值分别为1.95 μg/mL和3.91 μg/mL。与槲皮素不同，这两种物质有效抑制幽门螺杆菌生长的机制并不涉及强毒因子脲酶，这为开发可用于治疗幽门螺杆菌感染的创新药物提供了研究基础^[76]。

2.2 抗炎活性

一些杜松烷型倍半萜类化合物具有抗炎活性，如化合物arteannoides B (121) 和arteannoides C (122) 能抑制脂多糖(LPS) 诱导的原代264.7巨噬细胞中一氧化氮(NO) 的产生，从而表现出抗炎活性，IC₅₀值分别为4.50 μmol/L和2.90 μmol/L^[3]；7-hydroxy-3, 4-dihydrocadalene (44) 和7-hydroxy- cadalene (45) 除具有抗菌作用外，还具有抗NF-κB活性，其中7-hydroxy-cadalene (45) 的活性最强，IC₅₀值(16.5±2.2) μmol/L。另外，7-hydroxy-3, 4-dihydrocadalene (44) 也能通过激活抗氧化剂Nrf2途径表现抗炎活性^[56]；Zhu等从丰肉结海绵Gelliodes carnosa相关真菌中分离得到的hypocreaterpenes A和B以及一个已知的杜松烷型化合物1R, 6R, 7R, 10S-10-hydroxy-4(5)-cadinen- 3-one均对LPS处理的RAW264.7细胞产生NO有抑制作用。其中化合物1R, 6R, 7R, 10S-10-hydroxy- 4(5)-cadinen-3-one在1 μmol/L时表现出中等的抗炎活性，平均最大抑制率(E_max) 为10.22%^[77]。

2.3 降糖活性

化合物curcujinone A (66) 和curcujinone B (33) 能够增加HepG2细胞葡萄糖消耗，在10 μmol/L时葡萄糖消耗增加45%，具有较好的抗糖尿病活性^[4]；化合物cornucadinosideA–E (112–116) 在10 μmol/L浓度下对α-葡萄糖苷酶具有显著的抑制活性。与临床上用于控制血糖水平的阳性对照阿卡波糖相比，除cornucadinoside C (114) 外，都表现出与阳性对照相似的效果，尤其是cornucadinoside E (116) 比阿卡波糖更有效^[71]。

2.4 其他活性

以经典抗肿瘤药物紫杉醇为阳性对照，化合物2β, 7, 3-trihydroxycalamenene 3-O-β-D-glucoside (110) 对HeLa和HepG2人癌细胞株具有中度的细胞毒活性，IC₅₀值分别为12.88 μmol/L和18.15 μmol/L^[69]；化合物curcumane C (100) 能够增加人脐静脉内皮细胞中NO的含量，对KCl引起的大鼠主动脉环收缩表现出明显的舒张作用，同时对苯肾上腺素引起的大鼠主动脉环收缩也有舒张作用。通过比较curcumane C对内皮完整(E+) 和内皮剥脱(E–) 的大鼠主动脉环的舒张作用，发现curcumane C对E+的松驰作用明显强于E–，E+和E–的E_max值分别为76.70%和41.44%^[68]。

3 杜松烷型倍半萜化合物生物合成研究

随着生物技术手段的进步，代表性杜松烷型倍半萜化合物(如青蒿素和棉酚) 的生物合成途径已被基本阐明，其合成生物学领域也取得突破性进展^{[6-9, 78]}。然而，大多杜松烷型倍半萜产物的生物合成研究仍停留在对其关键酶杜松烷型倍半萜合酶的研究上。该部分在简单介绍两个代表杜松烷型倍半萜化合物(青蒿素和棉酚) 的生物合成途径解析概况后，重点对该类倍半萜合酶的研究进展进行归纳总结。

3.1 青蒿素和棉酚的生物合成途径解析

青蒿素的生物合成途径^{[6, 78]}可以概括为：(1) FPP在紫穗槐-4, 11-二烯合酶(ADS) 的催化下，通过1, 6-和1, 10-环化生成关键中间体紫穗槐-4, 11-二烯；(2) 各种后修饰酶如紫穗槐二烯C-12氧化酶(CYP71AV1)、P450还原酶(CPR1)、细胞色素b5 (CYB5)、醇脱氢酶(ADH1)、醛脱氢酶(ALDH1) 以及双键还原酶(DBR2) 等，对紫穗槐-4, 11-二烯进行氧化、羟化、脱氢和还原，产生青蒿醇、青蒿醛、青蒿酸和二氢青蒿酸等重要的中间体；(3) 二氢青蒿酸经过一个过氧化物中间体，最终形成青蒿素(图 7)。

图 7 青蒿素生物合成途径示意图^[78] Fig. 7 Schematic diagram of artemisinin biosynthesis pathway^[78].

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棉酚的生物合成途径是在DCS催化FPP生成δ-杜松烯的基础上，经过P450单加氧酶、双加氧酶、醇脱氢酶等后修饰酶的催化，生成带有α，β-不饱和羰基的中间体，继而再通过芳构化最终偶联形成化合物棉酚^[8-9]，见图 8。

图 8 棉酚生物合成途径示意图^[8] Fig. 8 Schematic diagram of gossypol biosynthesis pathway^[8].

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3.2 杜松烷型倍半萜类合酶研究进展

图 9和表 2总结了近年来发现的杜松烷型倍半萜合酶的名称及其催化产物，并标识了其来源。从表 2可见，对植物和真菌来源的杜松烷型倍半萜合酶的研究最多，并且真菌来源中绝大多数为担子菌。

图 9 杜松烷型倍半萜合酶主要产物示意图 Fig. 9 Schematic diagram of major products of cadinane sesquiterpene synthases.

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表 2 杜松烷型倍半萜合酶名称、来源及其主要产物 Table 2 Names, origins and main products of cadinane sesquiterpene synthases

Classification	Name (Genbank number)	Origin	Main product	Reference
Plant	LaCADS (JX401282)	Lavandula angustifolia	τ-cadinol	[83]
	Cdn1-C4 (AF270425)	Gossypium arboreum	(+)-δ-cadinene	[84]
	Cad1-A (Y18484)	Gossypium arboreum	(+)-δ-cadinene	[85]
	Cad1-C3	Gossypium arboreum L.	(+)-δ-cadinene	[86]
	ZmTPS7	Maize (Zea mays)	τ-cadinol	[87]
	PnCO/CDS (KU953958)	Black pepper (Piper nigrum)	δ-cadinol	[88]
	CAD1	Gossypium arboreum	δ-cadinene	[89]
	CDN1-C1	Gossypium arboreum	δ-cadinene	[90]
	HaCS (DQ016668)	Helianthus annuus L.	δ-cadinene	[91]
	SasesquiTPS1	Santalum album L.	γ-muurolene	[92]
	ADS	Artemisia annua L.	amorpha-4, 11-diene	[93]
Fungi (basidiomycetes)	BvCS (KU668561)	Boreostereum vibrans	δ-cadinol	[94]
	Cop3 (EAU88892)	Coprinus cinereus	α-muurolene	[95]
	Cop4 (EAU85540)	Coprinus cinereus	δ-cadinene	[95]
	Ompl	Omphalotus olearius	α-muurolene	[96]
	Omp4	Omphalotus olearius	δ-cadinene	[96]
	Omp5a and Omp5b	Omphalotus olearius	γ-cadinene	[96]
	Stehi1\|128017	Stereum hirsutum	δ-cadinene	[97]
	GME3634 (KX281943)	Lignosus rhinocerotis	α-cadinol	[98]
	GME3638 (KX281944)	Lignosus rhinocerotis	(+)-torreyol (δ-cadinol)	[98]
	AcTPS5	Antodia cinnamomea	τ-cadinol	[99]
Fungi (ascomycetes)	Hyp2 (AHY23921)	Hypoxylon sp. E7406B	δ-cadinene	[100]
Bacteria	SSCG_02150	Streptomyces clavuligerus	(-)-δ-cadinene	[101]
	SSCG_03688	Streptomyces clavuligerus	(+)-τ-muurolol	[101]
	YP_003124367	Chitinophaga pinensis DSM 2588	γ-cadinene	[102]
	RoseRS_3509	Roseiflexus sp. RS-1	τ-muurolol	[103]
	Rcas_0622	Roseiflexus castenholzii DSM 13941	τ-muurolol	[103]

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近年来对杜松烷型倍半萜合酶的研究已不局限于杜松烷型倍半萜合酶的挖掘、表征及酶功能的验证，而是扩展到新颖或已知杜松烷型倍半萜合酶的结构与功能的关系以及催化机制研究。该节将从酶催化机制及关键氨基酸的定点突变对活性的影响两个方面对杜松烷型倍半萜合酶的研究进展进行总结。

3.2.1 杜松烷型倍半萜合酶的催化机制

杜松烷型倍半萜合酶催化底物FPP形成最终产物的反应机理并未阐明，以δ-杜松烯合酶(DCS) 催化生成δ-杜松烯为例(图10)，目前存在3种具有理论和证据支持的催化机理：(1) FPP离子化和异构化生成(3R)-橙花苷二磷酸((3R)-NDP)，后者经C2-C3键旋转、1, 10-环化、1, 3-氢迁移以及1, 6-环化等一系列反应生成杜松烯阳离子；(2) FPP生成(3R)-NDP，后者经C2-C3键旋转、1, 6-环化、1, 3-氢迁移、1, 10-环化、1, 5-氢迁移等反应生成杜松烯阳离子；(3) FPP直接进行1, 10-环化生成瞬态反, 反-吉马烯阳离子，后者经1, 3-氢迁移以及去质子反应生成吉马烯D，吉马烯D通过质子转移和构象变化进行1, 6-环化以生成杜松烯阳离子。以上3种途径生成的杜松烯阳离子去质子，最终生成δ-杜松烯^[79-82]。

图 10 催化反应机理^[79-82] Fig. 10 Catalytic reaction mechanisms of DCS^[79-82].

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3.2.2 杜松烷型倍半萜合酶氨基酸定点突变对酶活性的影响

对杜松烷型倍半萜合酶的研究以DCS最为深入，DCS特异性较高，仅能催化FPP产生(+)-δ-杜松烯一种产物^[80]。与其他Ⅰ型萜类环化酶相同，DCS的D螺旋上含有一个天冬氨酸富集的DDTYD基序，用于结合Mg²⁺ A和Mg²⁺ C，不同的是，H螺旋上用于结合Mg²⁺ B的NSE/DTE基序在DCS中被DDVAE基序取代。Gennadios等^[9]对D₃₀₇DTYD₃₁₁和D₄₅₁DVAE₄₅₅基序的突变研究表明，保守基序对于金属离子的结合和酶的催化活性具有重要作用。

关键氨基酸的突变会影响DCS的产物特异性^{[80-81, 104]}。通过G螺旋的N₄₀₃和L₄₀₅定点饱和突变，发现突变株N403P/L405H的主产物从(+)-δ-杜松烯变成吉马烯D-4-醇；对位于N₄₀₃和L₄₀₅对侧，空间上更接近底物异戊二烯链的W₂₇₉进行定点突变，突变体W279A的催化产物中吉马烯D-4-醇的含量高达90%；N端多肽片段(NTS) 截短后，随着截短长度的增加，产物中吉马烯D-4-醇的比例增加。以上结果中吉马烯D-4-醇的产量均增加，说明G螺旋、W₂₇₉以及NTS在保护底物碳正离子免受外部溶剂的影响方面起着重要作用，其特定变化可以改变产物的特异性。

4 讨论与展望

杜松烷型倍半萜类天然产物在自然界中分布广泛，通过对近4年来新颖杜松烷型化合物结构的归纳可发现：该类产物因双环并环方式的不同(1, 6-顺反、1, 6-顺顺)，可生成构型各异的杜松烷骨架；不同数量、不同构型羟基的取代则产生更多的同分或立体异构体；官能团的氧化及还原、其他结构片段的引入、骨架的二聚或多聚均增加了杜松烷型倍半萜类天然产物的结构多样性。随着对天然来源倍半萜类化合物研究的不断深入，更多复杂的杜松烷型倍半萜类产物亟待发现，且对不同构型该类产物的鉴定也需要引起学者的重视。

杜松烷型倍半萜类天然产物除了结构复杂多样外，还具有多种多样的药理活性，如7-hydroxy- 3, 4-dihydrocadalene (44) 与阳性药槲皮素的作用机制不同，具有较强的抗幽门螺杆菌活性；cornucadinoside E (116) 表现出比阿卡波糖更优的降糖活性；不同构型羟基取代的杜松醇则表现出不同强度的抗真菌活性。随着人们对该类化合物的不断探索，对其药理活性的研究也更加广泛，值得注意的是，化合物结构的多样性对药理活性有较大影响，对该类产物构效关系的研究亟待加强及完善。

杜松烷型倍半萜合酶来源广泛，其结构与功能的研究也取得了较大进展，尤其以植物来源的δ-杜松烯合酶的研究最为透彻。但是，其他杜松烷型倍半萜合酶还有待深入研究，尤其是对不同构型杜松烷型倍半萜合酶生成机制的关注度不够，没有意识到非对映异构体可能是由不同环化机制而生成。因此，杜松烷型倍半萜合酶的研究仍任重而道远，只有更全面、更系统地分析该类酶结构与功能的关联性，才能不断完善人们对该类倍半萜合酶催化机理的认识，才有利于通过合成生物学方法产生正确立体构型的杜松烷型倍半萜产物，以用于新药研发。

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