eprintid: 10114468 rev_number: 22 eprint_status: archive userid: 608 dir: disk0/10/11/44/68 datestamp: 2020-12-17 11:19:05 lastmod: 2025-02-12 07:12:19 status_changed: 2020-12-17 11:19:05 type: thesis metadata_visibility: show creators_name: Zhao, Jianxiong title: Synthesis of Tetrahydroisoquinoline Alkaloids using Norcoclaurine Synthase and Phosphate Buffer mediated Pictet-Spengler Reactions ispublished: unpub divisions: UCL divisions: A01 divisions: B04 divisions: C06 divisions: F56 note: Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. abstract: Tetrahydroisoquinoline (THIQ) alkaloids are a family of structurally diverse natural products with medicinal properties, such as anti-bacterial and anti-tumour effects. Recently, the use of biocatalysts in organic synthesis offers a new possibility to access these molecules, which is more cost-effective than traditional isolation methods and chemical synthesis. Norcoclaurine synthase (NCS) is a key enzyme that catalyses the Pictet-Spengler reaction (PSR) of dopamine and 4-hydroxyphenylacealdehyde in the biosynthetic pathway of morphine. In this thesis, NCS and phosphate mediated PSRs towards bioactive THIQ alkaloids have been explored. In Chapter 2, non-natural phenethylamine analogues and functionalized aldehydes have been used in the developed one-pot, two-step chemoenzymatic routes to antibacterial (S)-trolline and analogues. No general PSR side product ortho-THIQs were observed with NCS, and product purification could be typically achieved by an acid-base extraction method using the green solvent dimethyl carbonate. Compared to the previous asymmetric synthesis of trolline, this chemo-enzymatic route using NCS is more productive, sustainable and atom-efficient. In Chapter 3, phosphate was unprecedentedly found to catalyse the PSRs between metahydroxyl phenylethylamines and unreactive ketones in basic buffer condition with methanol as co-solvent, efficiently giving 1,1'-disubstituted and spiro-THIQ alkaloids in excellent yields. A range of ketones such as monocyclic, bicyclic and acyclic ketones have been demonstrated to be accepted, showing broad synthetic applicability to access diverse THIQs. In Chapter 4, NCS was firstly confirmed to be capable of tolerating ketones in the PSR, leading to asymmetric formation of 1,1'-disubstituted and spiro-THIQ alkaloids. Apart from HPLC, Marfey‘s reagent has been used to derivatize the THIQ products, which assists the stereoselectivity determination. A variety of ketones were accepted by NCS and mutants, particularly tetralones, phenyl acetones and monocyclic ketones. In Chapter 5, NCS has been coupled with transaminase to generate THIQ alkaloids in cascade reactions using primary amines. Transamination of amines can produce aldehyde intermediates, which are directly consumed in the subsequent NCS mediated PSRs without isolation of the aldehydes. Different sources of transaminases combined with the wild-type NCS were investigated on a number of functionalized amines. date: 2020-11-28 date_type: published oa_status: green full_text_type: other thesis_class: doctoral_open thesis_award: Ph.D language: eng thesis_view: UCL_Thesis primo: open primo_central: open_green verified: verified_manual elements_id: 1827785 lyricists_name: Zhao, Jianxiong lyricists_id: JXZHA40 actors_name: Zhao, Jianxiong actors_id: JXZHA40 actors_role: owner full_text_status: public pagerange: 1-331 pages: 331 event_title: UCL (University College London) institution: UCL (University College London) department: Chemistry thesis_type: Doctoral citation: Zhao, Jianxiong; (2020) Synthesis of Tetrahydroisoquinoline Alkaloids using Norcoclaurine Synthase and Phosphate Buffer mediated Pictet-Spengler Reactions. Doctoral thesis (Ph.D), UCL (University College London). Green open access document_url: https://discovery-pp.ucl.ac.uk/id/eprint/10114468/1/J%20Zhao%20PhD%20thesis%20final.pdf