Biomimetic Phosphate-Catalyzed Pictet-Spengler Reaction for the Synthesis of 1,1′-Disubstituted and Spiro-Tetrahydroisoquinoline Alkaloids

Article abstract of DOI:10.1021/acs.joc.9b00527

Tetrahydroisoquinoline (THIQ) alkaloids are an important group of compounds that exhibit a range of bioactivities. Here, a phosphate buffer-catalyzed Pictet-Spengler reaction (PSR) using unreactive ketone substrates is described. A variety of 1,1′-disubst

Full text of DOI:10.1021/acs.joc.9b00527

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Article
A Biomimetic Phosphate Catalyzed Pictet-Spengler Reaction for the
Synthesis of 1,1’-Disubstituted and Spiro-Tetrahydroisoquinoline Alkaloids
Jianxiong Zhao, Daniel Mendez-Sanchez, John M. Ward, and Helen C. Hailes
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00527 • Publication Date (Web): 16 May 2019
Downloaded from http://pubs.acs.org on May 16, 2019
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A Biomimetic Phosphate Catalyzed Pictet-Spengler
Reaction for the Synthesis of 1,1'-Disubstituted and
Spiro-Tetrahydroisoquinoline Alkaloids
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Jianxiong Zhao†, Daniel Méndez-Sánchez†, John M. Ward‡ and Helen C. Hailes†*
† Department of Chemistry, University College London, Christopher Ingold Building, 20 Gordon
Street, London, WC1H 0AJ, UK;
‡ Department of Biochemical Engineering, University College London, London, WC1E 6BT, UK.
Corresponding Author: h.c.hailes@ucl.ac.uk
ABSTRACT
HO
HO
phosphate buffer
O
+
NH
R1 R2
NH2
R1
R2
pH 9
R
R
More than 20 examples,
up to 97% yield and 1 g scale,
biomimetic and sustainable.
Tetrahydroisoquinoline alkaloids are an important group of compounds that exhibit a range of
bioactivities. Here, a phosphate buffer catalyzed Pictet-Spengler reaction (PSR) using unreactive
ketone substrates is described. A variety of 1,1'-disubstituted and spiro-tetrahydroisoquinoline
alkaloids were readily prepared in one-step and high yields, highlighting the general applicability of
this approach. This study features the role of phosphate in the aqueous-based PSR and provides an
atom-efficient, sustainable route to new THIQs.
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INTRODUCTION
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Tetrahydroisoquinolines (THIQs) are an important group of pharmacologically active compounds
exhibiting for example, anticancer, antimalarial, analgesic, antithrombotic, and central nervous
system (CNS)-related activities. A sub-group of THIAs, the benzylisoquinoline alkaloids (BIAs) are
a key family of natural products found in higher plants and mammals.1 The BIAs in particular have
attracted the attention of many researchers in recent years, giving rise to a range of patents and
publications.2-8 Amongst the THIAs, 1,1'-spiro compounds have proven to be synthetically
challenging to synthesize, and they include the antiplasmodial compound 1, natural product
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ochotensines 2 and 3, and trabectedin 4 (Figure 1).9-11
HO
OMe
RO
NH
HO
MeO
Me
Me
O
NMe
HO
MeO
H
S
AcO
O
H
NH
N
Me
N
O
OH
H
O
O
O
1
2 R = H, ochotensine
4 trabectedin (ET-743)
3 R = Me, ochotensimine antitumour chemotherapy drug
antiplasmodial
activity
Figure 1. Selected 1,1’-spiro tetrahydroisoquinoline alkaloids
Different strategies have been used to access THIAs, including natural product extraction from
plant sources, affording the desired alkaloids in low yields. In recent years, efforts have also been
focused on the expression of biocatalysts for use in the stereoselective synthesis of these alkaloids.
For example, in plants norcoclaurine synthases (NCSs) catalyze the first committed step in the BIA
biosynthetic pathway, between dopamine 5 and 4-hydroxyphenyl acetaldehyde (4-HPAA) and this
has been used in synthesis.12-15
The Pictet Spenglerase NCS has proven to be particularly tolerant towards a range of aldehydes
and more recently has been reported to accept ketones.16-20 While the use of NCS to generate 1,1'-
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substituted THIQs is a particularly powerful strategy in stereoselective synthesis, a complementary
method to access achiral compounds, or an approach that does not necessitate the production of
biocatalysts would also be highly valuable.
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Many methods have been reported to synthesize THIQs including the Pictet-Spengler or Bischler-
Napieralski reactions,21,22 but typically for these reactions, particularly when using ketones, high
temperatures, strong acids or superacids are required.23,24 An example includes the reaction of 1-(3-
hydroxyphenyl)-2-aminoethanol with cyclohexanone to give a spiro-oxazolidine which when fused
at 150 °C gave the 1,1'-spiro-hexanotetrahydroisoquinoline.25,26 Such reaction conditions are however
incompatible with less stable phenethylamines such as catechols. To overcome some of these
problems, Lewis Acids catalysts such as o-benzenedisulfonamide,27 titanium(IV) isopropoxide28 or
calcium bis-1,1,1,3,3,3-hexafluoroisopropoxide29 have been used (Scheme 1a and 1b), but there are
inherent limitations associated with the preparation of such catalysts including high costs or the
requirement of a drybox.29 In addition, the key phenolic groups must be protected or side products
can be formed. Phosphate salts are a useful alternative due to the lower costs and milder reaction
conditions that can be used.30 Indeed, we have previously reported the use of aqueous phosphate in a
Pictet-Spengler reaction (PSR) for the synthesis of THIQs (Scheme 1c).30 The reaction was extended
to a range of aromatic, aliphatic and heterocyclic aldehydes, but not with ketone substrates which are
more sterically challenging and less reactive.
Here, we describe the discovery that aqueous phosphate reaction conditions can also be used to
synthesize THIQs. The reaction conditions were optimized and applied to variously decorated
phenethylamines and a wide range of cyclic and acyclic ketones in high yield (Scheme 1d). Some of
the THIQs synthesized have also been reported to possess interesting bioactivities, including anti-
parasitic properties.10
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Previous work
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HO
R1
MeO
3 steps using Ti(O-ipr)4,
HCOOH-Ac2O and NaOH
a)
NH
R2 R3
NH2
R1
ketones
7
8
9
HO
R1
20 mol% Ca(HFIP)2, 3Å MS
HO
b)
NH
R2 R3
toluene, 100 oC
NH2
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R1
ketones
HO
KPi (0.1 M, pH 6),
HO
c)
NH
NH
MeCN, 35-50 oC
NH2
R1
R1
aldehydes
R2
This work
KPi (0.3 M, pH 9),
HO
HO
d)
methanol, 70 oC
NH2
R
R
ketones
Scheme 1. a,b) Reported Lewis acid catalysed PSRs with ketones; c) Previous aqueous phosphate-
mediated PSRs with aldehydes; d) PSRs with ketones reported in this work.
RESULTS AND DISCUSSION
Aqueous phosphate media has previously been used to produce norcoclaurine from dopamine 5 and
4-HPAA via a Pictet-Spengler reaction and the reaction was extended to a range of aldehyde
substrates.30 Despite this facile approach of using catechols to generate THIAs, an extension to ketone
substrates has received little attention, other than work by Tono et al who noted that acetone might
couple with dopamine in phosphate buffer (0.1 M, pH 7.2), although the product was not
characterized.31 In addition, the extraction of dopamine from the Chinese yam with acetone was
believed to form a THIA and characterization of plant acetone extracts from Aristolochia arcuata
highlighted a THIA formed from dopamine and acetone.32,33 The main challenge with the PSR
reaction using ketones is the relatively low reactivity, which combined with the sensitivity of
catechols can lead to the formation of many side products. However, inspired by the interesting NCS
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mediated PSR reaction with ketones it was decided to investigate whether an aqueous biomimetic
phosphate-based approach could also be developed.19
6
7
8
9
Firstly, to avoid side-reactions due to the oxidation of catechols such as dopamine 5, the antioxidant
sodium ascorbate was added to reactions.20 Cyclohexanone 6 was then used in a reaction with
potassium phosphate (KPi, 1 M) with acetonitrile as co-solvent at pH 6 and 70 °C and surprisingly,
the PSR product 7 was formed in 11% yield (Table 1，entry 1). Since different phosphate anions
predominate at different pHs, at pH 6 the major ion is H2PO4–, alternative pHs were explored.
Unsuprisingly, no product 7 was observed at pH 4, due to dopamine protonation, and pH 12 due to
the oxidation of dopamine which is prevalent at high basic pHs. However, at pH 9 the yield increased
to 16% (Table 1, entry 4; see SI Figure S1 for further data on the effect of pH). A pH of 9 was then
used as a suitable starting point for further reaction optimization. DFT and MP2 methods have been
used in a theoretical study exploring the phosphate-mediated PSR with 3-hydroxypehenethylamine
and formaldehyde, which suggested that at the lowest energy pathway required both HPO42- and
H2PO4– for optimal catalysis in the phosphate biomimetic reaction.34 At pH 9, HPO42- is the
predominant anion present (with some H2PO4–) and can facilitate both the deprotonation of the meta-
phenolic OH and abstraction of 8a-H in the isoquinolone intermediate.
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Typically, a co-solvent was required when developing the phosphate PSR reaction with aldehydes
where aldehyde solubility was poor so other co-solvents were investigated, also with a view to
enhancing yields. The polar aprotic solvents DMSO, DMF, and 1,4-dioxane together with the polar
protic solvents methanol, ethanol and isopropanol were investigated (Table 1 and SI Figure S2).
While DMSO and had little effect on the yield, it decreased when using DMF, 1,4-dioxane and
isopropanol. However, the reaction yields were higher with ethanol and in particular methanol (Table
1, Entry 6) which was superior to other co-solvents (Table 1, Entry 6), giving a 43% yield of 7. Further
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studies established that lower proportions of methanol (10%-40% v/v, data not shown) generated
similar yields of 7 and in the absence of co-solvent 36% of 7 was formed. This presumably reflects
the fact that in the case of 6 there were no solubility issues in water.
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Table 1. Initial optimization of the model reaction using 5 and 6 to give 7a
O
HO
HO
6
HO
HO
KPi (1 M)
+
NH
NH2
sodium ascorbate
18 h, 70 oC
8a
5
6
7
Entry
6 (equiv.)
1.3
KPi pH
Co-solvent
MeCN
MeCN
MeCN
MeCN
DMSO
EtOH
Yield 7 (%)b
1
2
6
4
11
0
1.3
3
1.3
12
9
0
4
1.3
16
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21
43
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46
81
97
5
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6
1.3
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7
1.3
9
MeOH
None
8
1.3
9
9
2.0
9
MeOH
MeOH
MeOH
10
11
5.0
9
10.0
9
aReactions conditions: dopamine 5 (15-25 mM), cyclohexanone 6 (20-150 mM) and sodium ascorbate
(1.0 equiv. relative to dopamine) on a 1 mL scale in 1 M KPi, pH 9 and 50% co-solvent (v/v) at 70 °C;
bYields were determined by analytical HPLC.
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To improve the synthetic utility, the reaction temperature was increased to 80 °C and 90 °C with
little effect. Upon increasing the number of equivalents of 6 from 1.3 equiv. to 2, 5, and 10 equiv., in
the latter case, 7 was formed in quantitative yield (Table 1, entry 11), so this was used in further
experiments. The effect of using lower KPi concentrations was also investigated using 5 and 6 (SI,
Table S1). Concentrations of 0.1 to 1 M KPi gave 7 in 97% yield, and below 0.1 M the yield of 7
decreased. To ensure sufficient KPi was present, a 0.3 to 0.5 M KPi concentration was therefore
selected. The effect of the dopamine 5 concentration in the reaction was also explored (SI, Table S2).
The yield remained constant with concentrations of up to 0.3 M, decreasing to 48% at 1 M of 5 when
solubility issues were encountered.
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With optimized reaction conditions in hand we were curious to understand the requirement for
phosphate in the reaction. Alternative buffers or bases were used at pH 9 including KOH, KHCO3-
K2CO3 (0.5 M), Na3BO3 (0.5 M) and Na2SO3 (saturated) together with water alone (SI, Table S3).
When water, water adjusted to pH 9 with KOH, or Na3BO3 solution were used, 7 was formed in trace
amounts in reactions with 10 mM of 5 (SI, Table S3). These increased to 8-15% yields in reactions
using 50 mM of 5 (SI, Table S4). Interestingly, with KHCO3-K2CO3 and Na2SO3 at pH 9 yields of
24% and 43% with 10 mM 5 were noted, increasing to 63% and 89% with 50 mM 5, respectively. At
both dopamine concentrations the highest yields were still observed with KPi. The role of phosphate
in previous experiments for aldehyde-PSRs has been probed using DFT and MP2 methods in a
theoretical study.34 The proposed reaction scheme for 3-hydroxyphenethylamine and formaldehyde
involved both HPO42- and H2PO4– having a role in the formation of a complex with the iminium
intermediate, and after cyclisation, H2PO4– assisting in the deprotonation at 8a-H of the isoquinolone,
while also being complexed to the amine proton. The lower yields observed with KHCO3-K2CO3 of
24% (10 mM 5) and 63% (50 mM 5) may reflect that the trigonal planar geometry of carbonate is
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unlikely to be able to perform a similar role of deprotonation and amine proton complexation as
readily as H2PO4– (or potentially HPO42-) in the re-aromatization step, compared to tetrahedral
phosphate. The relatively high yields with Na2SO3 were interesting and may be due to its trigonal
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pyramidal structure, enabling the re-aromatization step in a similar fashion to KPi, combined with the
reducing environment it provides. Overall, KPi gave rise to the highest yields so was used in further
experiments. It was also noted that in the reaction between 5 and 6 for the KPi concentrations used,
no ortho-regioisomer was detected presumably due to steric reasons.35
With suitable reaction conditions established, the general applicability of the reaction was explored
for the synthesis of a range of 1,1'-disubstituted and spiro-THIQ alkaloids (Scheme 2). Reactions
were monitored by 1H NMR spectroscopy, due to the reported challenges with product isolation.29 In
addition, to confirm the NMR data, for several reactions, yields were confirmed by HPLC analysis.
The phosphate mediated PSR could tolerate a range of methyl ketones, giving 8-12 in 54-95% yield
when using aliphatic ketones. The reaction yields were greater for 8 and 9, reflecting the influence of
the increasing alkyl chain length and associated steric effects in the intermediates and subsequent
cyclizations to give products 10-12. For the aromatic ketones acetophenone or phenyl acetone giving
13 and 14, respectively, again poor reactivities were observed, reflecting unfavorable steric
interactions in the cyclization step to generate the THIQs. The introduction of a trifluoromethyl group
however was readily achieved giving 15 in 93% yield.
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KPi (0.3 M, pH 9), methanol
HO
HO
sodium ascorbate, 70 oC
ketones
NH
R1 R2
NH2
R
R
6
7
8
9
HO
HO
HO
HO
HO
HO
HO
HO
HO
NH
NH
9b 92% (33%)
NH
NH
NH
HO
10
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8a 95% (32%)
10b 78% (43%)
11b 54% (34%)
12b 60% (41%)
HO
HO
HO
HO
HO
HO
HO
HO
HO
HO
NH
NH
NH
NH
Ph
13b 11% (4%)
NH
Ph
F3C
16a 70% 61%)
17a 80%
(67%)
14a 25% (3%)
15b 93% (88%)
HO
HO
HO
HO
HO
HO
HO
HO
HO
HO
NH
NH
NH
NH
NH
O
18a 75%
(53%)
19a 83% (65%)
HO
HO
20a 97% (74%)
HO
21a 95% (77%)
7a 97% (70%)
HO
HO
F
HO
NH
NH
NH
NH
NH
HO
OH
23b 21% (7%)
24b 74% (55%)
25b 55% (50%)
26b 57% (37%)
22a 70% (57%)
Scheme 2. Application of the phosphate catalyzed PSR to synthesize 1,1'-disubstituted and spiro-
THIQ alkaloids. Typical reactions conditions: dopamine 5 (15-25 mM), ketone (20-150 mM) and
sodium ascorbate (1.0 equiv. relative to dopamine or the corresponding phenethylamine) were reacted
together on a 1 mL scale in 0.3 M KPi, pH 9 and methanol (50% v/v of methanol and ketone
combined) at 70 °C. Small scale reactions were performed in duplicate or triplicate. Yields were
1
determined by H NMR spectroscopy with an internal standard (maleic acid), and also by HPLC
analysis (see SI, Table S5 for HPLC retention times) for several examples to confirm the data; a 10
equiv. of the corresponding ketones were used; b50 equiv. of the corresponding ketones were used.
All products were isolated (yields are in brackets) either from these small-scale reactions or larger
reactions and purified, using the acid-base extraction method or preparative HPLC, for
characterization purposes.
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The introduction of a third cyclic or heterocyclic ring could more widely be introduced into the
THIA scaffold, following the model reaction to give 7. Using 3- or 4-methyl cyclohexanone readily
gave 16 and 17 in 70% and 80% yield, respectively. Similarly, with 4-isopropyl cyclohexanone, 18
was generated in 75% yield and using tetrahydro-4H-pyran-4-one 19 was formed 83% yield. When
using cyclobutanone and cyclopentanone THIAs 20 and 21 were formed in 97% and 95% yield,
comparable yields to when using 6, highlighting that other ring sizes can readily be used in the
phosphate catalyzed Pictet-Spengler condensation. Furthermore, the use of 1- or 2-indanone afforded
the tetracyclic ochotensine9 derivatives 22 and 23 in 70% and 21% yields, respectively.
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In addition to using alternative ketone substrates, selected substituted phenethylamines were
investigated (Scheme 2). 2-(3-Hydroxyphenyl)ethylamine20 was used with 6 to synthesize 24, a
compound previously synthesized in 2 steps and 10% yield and reported to possess anti-malarial
properties.10 A yield of 74% was achieved and the product was isolated by preparative HPLC in 53%
yield. The fluorinated analogue 4-fluoro-3-hydroxy phenethylamine was also used to give 25 in 55%
yield. A regioisomer of dopamine, 5-(2-aminoethyl)benzene-1,3-diol,36 which will provide more
unfavorable steric interactions was investigated and gave 26 in a reasonable 57% yield.
To highlight the utility of this methodology, the synthesis of 7 and 20 as selected compounds were
1
then performed on a 1 g scale. The reaction yields by H NMR spectroscopy were 97% and at this
larger scale it was possible to isolate the materials using an acid-base extraction method to give 7 in
40% yield and 20 in 51% yield.
The use of a ketone possessing an ester functionality for subsequent ring cyclisation was also
investigated to establish a reaction cascade to form an additional ring, as this strategy with an
aldehyde has been successfully used to generate the anti-bacterial trolline.20 Using the ketone KPi
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reaction conditions established, 5 was reacted with commercially available methyl levulinate 27 to
form a linear intermediate 28 with a C-1 quaternary carbon. Spontaneous cyclisation by amine
nucleophilic attack at the ester carbonyl, following the favored 5-exo-trig mode, afforded lactam 29
in 50% yield (by 1H NMR spectroscopy) (Scheme 3).
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HO
HO
O
KPi (0.3 M, pH 9)
HO
HO
NH
+
NH2
sodium ascorbate,
MeOH, 18 h, 70 oC
O
OMe
5
27
28
OMe
O
cyclises
HO
HO
HO
HO
N
N
O
O
trolline:20 anti-bacterial and
anti-viral properties
29
50% yield by 1H NMR
Scheme 3. Application of the KPi catalysed PSR with 27 in a cascade reaction.
CONCLUSION
In summary a biomimetic approach for the synthesis of 1,1’-disubstituted and spiro-THIQs has
been established using a Pictet-Spengler reaction with unactivated ketones. The reaction is readily
performed in methanol/phosphate buffer at pH 9 and 70 °C: these are significantly milder reaction
conditions than those previously reported. The reaction successfully used methyl ketones, cyclic
ketones and aromatic ketones with phenethylamines bearing a meta-hydroxyl group. Overall, this
study provides a low-cost and sustainable way of making C-1,1' disubstituted THIQ alkaloids using
phosphate buffer, to afford a range of products in high yields using a facile procedure.
EXPERIMENTAL
General Information. All chemicals were obtained from commercial suppliers and used as
received. Small- scale reactions were heated using a BIOER Mixing block MB-102, and the scale-up
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reactions were heated using Heidolph MR Hei-Tec type heating mantle. Thin layer chromatography
was carried out using Merck TLC Silica gel 60 F254 plates and products were visualized using
combinations of UV light (254 nm), potassium permanganate and phosphomolybdic acid staining
solutions. Column chromatography was carried out using silica gel (particle size 40–60 μm). Infrared
(IR) spectra were recorded using a Perkin Elmer Spectrum 100 FT-IR Spectrometer or a Bruker Alpha
Platinum-ATR, operating in ATR mode. 1H NMR spectra were recorded on Bruker Avance 400, 500,
600 and 700 MHz spectrometers at 25 °C, using the residual protic solvent stated as the internal
standard. Chemical shifts are quoted in ppm to the nearest 0.01 ppm using the following
abbreviations: s (singlet), d (doublet), t (triplet), q (quartet), qn (quintet), sext (sextet), dd (doublet of
doublets), dt (doublet of triplets), m (multiplet) defined as all multi-peak signals where overlap or
complex coupling of signals make definitive descriptions of peaks difficult. The coupling constants
are defined as J and quoted in Hz. 13C{1H} NMR spectra were recorded at 100, 125, 150 or 175 MHz
on Bruker Avance 400, 500, 600 and 700 MHz spectrometers at 25 °C using the stated solvent as
standard. Chemical shifts are reported to the nearest 0.1 ppm. Melting points were measured with a
Gallenkamp apparatus and were uncorrected.
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Mass spectra were obtained using a Waters Acquity UPLC SQD (using a linear gradient of 5-95%
of acetonitrile over 5 min, with a C8 column, and flow rate of 0.6 mL/min) and Waters LCT Premier
XE ESI Q-TOF mass spectrometer in the Department of Chemistry, UCL.
1
Determination of yields using H NMR spectroscopy. Reactions were set up in duplicate (1 mL
scale) in eppendorf tubes which were shaken at 70 °C for 20 h. The reaction mixture was transferred
to a round-bottomed flask and evaporated to remove the methanol. Water was then removed on a
freeze-drier to obtain a solid, which was dissolved in a solution of maleic acid (CD3OD:D2O = 1:3, 1
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mL) and characterized by H NMR spectroscopy. The concentration of the maleic acid was half of
the starting material dopamine. The peak integration of maleic acid proton (δ = 5.89 ppm) was
calibrated as 1.00, and the integration (×100%) of one of the product aromatic protons was used to
determine the NMR yield.
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HPLC methods
Analytical HPLC methods. HPLC analysis was carried out on an Agilent 1260 Infinity HPLC with
mobile phase (A: water with 0.1% TFA; B: acetonitrile) in a gradient of A/B = 90%/10% at 0-1 min,
A/B = 90%/10% to A/B = 30%/70% at 1-6 min, 100% B at 6-6.5 min, A/B = 90%/10% at 6.5-10
min. Each injection volume was 10 μL. The column was an ACE 5 C18 reverse phase column (150
mm × 4.6 mm). The flow rate was 1 mL/min and detection wavelength was 280 nm. The retention
time of each compound is given in the SI, Table S5.
Preparative HPLC methods. Preparative HPLC was carried out on a Dionex 580 HPLC system,
including P580 Pump, ASI-100 Automated Sample Injector and PDA-100 Photodiode Array
Detector. A C18 reverse phase column, Agilent ZORBAX 300SB-C18 (250 mm × 9.4 mm, 5 μm) was
used for purifications. The detection wavelength was 280 nm and the flow rate was 2 mL/min.
Chromeleon Client Program software was used to monitor the HPLC traces.
Method I Mobile phase (A: water with 0.1% TFA; B: acetonitrile with 0.1% TFA) in a gradient of
A/B = 95%/5% at 0-6 min, A/B = 95%/5% to A/B = 55%/45% at 6-10 min, A/B = 55%/45% at 10-
15 min, A/B = 55%/45% to A/B = 10%/90% at 15-16 min, A/B = 10%/90% at 16-18 min, A/B =
10%/90% to A/B = 95%/5% at 18-20 min, A/B = 95%/5% at 20-25 min.
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Method II Mobile phase (A: water with 0.1% TFA; B: acetonitrile with 0.1% TFA) in a gradient of
A/B = 95%/5% at 0-10 min, A/B = 95%/5% to A/B = 5%/95% at 10-12 min, A/B = 5%/95% at 12-
13 min, A/B = 5%/95% to A/B = 95%/5% at 13-14 min, A/B = 95%/5% at 14-30 min.
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Method III Mobile phase (A: water with 0.1% TFA; B: acetonitrile with 0.1% TFA) in a gradient
of A/B = 85%/15% at 0-30 min.
3',4'-Dihydro-2H-spiro[cyclohexane-1,1'-isoquinoline]-6',7'-diol hydrochloride.19 (7.HCl)
To a solution of dopamine hydrochloride (19 mg, 0.10 mmol) and sodium ascorbate (20 mg, 0.10
mmol) in KPi buffer (0.3 M, pH 9, 0.5 mL) and methanol (0.5 mL) was added cyclohexanone (104
μL, 1.0 mmol). The reaction mixture was shaken at 70 °C for 18 h and monitored by analytical HPLC.
The reaction mixture was diluted to ~7 mL with water and directly purified using preparative HPLC
method I. Fractions were combined, exchanged with HCl (1 M) and evaporated to obtain 7.HCl (19
mg, 70%) as a solid. The NMR yield of the reaction (97%) was determined following the general
procedure described. The reaction was scaled-up using 5.HCl (1.00 g, 5.27 mmol) sodium ascorbate
(1 equiv. with respect to dopamine) in KPi buffer (0.3 M, pH 9, 52.7 mL) and methanol (52.7 mL),
and 6 was added (5.48 mL, 52.7 mmol). The reaction mixture was shaken at 70 °C for 20 h, then the
pH adjusted to 3 by the addition of HCl (2 M). The solvent was removed in vacuo, and the residue
suspended in acetonitrile at 0 ºC. Finally, the mixture was filtered and solvent removed in vacuo to
give 7.HCl (0.491 g, 40%). 1H NMR (600 MHz; CD3OD) δ 6.76 (s, 1H), 6.57 (s, 1H), 3.41 (t, J = 6.4
Hz, 2H), 2.96 (t, J = 6.4 Hz, 2H), 2.10–1.97 (m, 4H), 1.88–1.77 (m, 3H), 1.70–1.60 (m, 2H), 1.52–
1.42 (m, 1H); C{1H} NMR (151 MHz; CD3OD) δ 146.4, 146.0, 129.9, 123.1, 116.1, 113.3, 61.0,
13
38.6, 36.8, 26.2, 25.3, 21.7; m/z [ES+] 234 ([MH]+, 100%).
1,1-Dimethyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride.33 (8.HCl)
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Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 963 μL) in a capped Eppendorf tube. Acetone (37 μL, 0.50 mmol)
was then added and the reaction mixture was shaken under argon at 70 °C. After 18 h, the acetone
was removed in vacuo. The remaining solution was freeze-dried and the NMR yield (95%)
determined following the general procedure described. The reaction was also performed in duplicate
to confirm the NMR yield and these two reaction products were combined and purified using
preparative HPLC method I. Fractions were combined, exchanged with HCl (1 M) and evaporated at
55 °C to obtain 8.HCl as a white solid (7.4 mg, 32%). 1H NMR (400 MHz; CD3OD) δ 6.70 (s, 1H),
6.57 (s, 1H), 3.46 (t, J = 6.4 Hz, 2H, 3-H2), 2.96 (t, J = 6.4 Hz, 2H, 4-H2), 1.67 (s, 6H, 2 × CH3);
13C{1H} NMR (100 MHz; CD3OD) δ 146.5, 146.2, 129.6, 122.3, 116.1, 112.7, 58.1, 38.8, 28.5, 26.0;
m/z [ES+] 194 ([MH]+, 100%).
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1-Ethyl-1-methyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride. (9.HCl)
To a solution of dopamine hydrochloride (19 mg, 0.10 mmol) and sodium ascorbate (20 mg, 0.10
mmol) in KPi buffer (0.3 M, pH 9, 1 mL) and methanol (0.55 mL) was added butanone (0.45 mL, 5.0
mmol). The reaction mixture was shaken at 70 °C for 18 h and monitored by analytical HPLC. The
reaction mixture was diluted to 25 mL with water, washed with ethyl acetate (3 × 20 mL) and
evaporated in vacuo to remove residual ethyl acetate, then directly purified using preparative HPLC
method II. Fractions were combined, exchanged with HCl (1 M) and evaporated to give 9.HCl (8.0
mg, 33%) as a white solid. The NMR yield of the reaction (92%) was determined following the
1
general procedure described. Mp. 129-133 °C (H2O); nmax (film) 2970, 2792, 1591, 1523 cm–1; H
NMR (600 MHz; CD3OD) δ 6.64 (s, 1H), 6.58 (s, 1H), 3.50–3.36 (m, 2H), 3.03–2.84 (m, 2H), 2.02
(q, J = 7.2 Hz, 2H), 1.63 (s, 3H), 0.98 (t, J = 7.2 Hz, 3H); 13C{1H} NMR (151 MHz; CD3OD) δ 146.5,
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146.1, 128.7, 122.9, 116.2, 113.0, 61.2, 39.0, 34.5, 26.0, 25.9, 8.1; m/z [ES+] 208 ([MH]+, 100%);
m/z [HRMS ES+] calcd for C12H18NO2 208.1332 [MH]+, found 208.1332.
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1-Methyl-1-propyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride. (10.HCl)
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Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (235 μL) in a capped Eppendorf tube. 2-
Pentanone (265 μL, 2.50 mmol) was then added and the reaction mixture was shaken under argon at
70 °C. After 20 h the methanol was removed in vacuo and the NMR yield (78%) determined following
the general procedure described. Two further duplicate reactions were performed, and the two
reaction products combined and purified using preparative HPLC method I. Fractions were combined,
exchanged with HCl (1 M) and evaporated at 55 °C to give 10.HCl (11 mg, 43%) as a white solid.
Mp. 237-239 °C (H2O); nmax (film) 3341, 3127, 2958, 1593, 1530 cm–1; 1H NMR (600 MHz; CD3OD)
δ 6.65 (s, 1H), 6.58 (s, 1H), 3.49–3.37 (m, 2H), 3.03–2.83 (m, 2H), 1.98–1.90 (m, 2H), 1.64 (s, 3H),
1.49–1.41 (m, 1H), 1.33–1.25 (m, 1H), 0.98 (t, J = 7.2 Hz); C{1H} NMR (151 MHz; CD3OD) δ
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146.5, 146.1, 128.9, 122.8, 116.2, 113.0, 60.9, 44.1, 39.0, 26.4, 26.0, 17.8, 14.4; m/z [ES+] 222
([MH]+, 100%); m/z [HRMS ES+] calcd for C13H20NO2 222.1489 [MH]+, found 222.1489.
1-Butyl-1-methyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride. (11.HCl)
Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (191.6 μL) in a capped Eppendorf tube. 2-
Hexanone (308.4 μL, 2.50 mmol) was then added and the reaction mixture shaken under argon at 70
°C. After 20 h the NMR yield (54%) was determined following the general procedure described. Two
further duplicate reactions were performed and these two reaction products were combined and
purified using preparative HPLC method III. Fractions were combined, exchanged with HCl (1 M)
and freeze dried to give 11.HCl (4.6 mg, 34%) as a white solid. Mp. > 250 °C (H2O); nmax (film) 3255,
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2957, 1599, 1392 cm–1; 1H NMR (600 MHz; CD3OD) δ 6.65 (s, 1H), 6.58 (s, 1H), 3.49–3.38 (m, 2H),
3.04–2.93 (m, 1H), 2.89 (dt, J = 17.0, 5.4 Hz, 1H), 2.00–1.93 (m, 2H), 1.63 (s, 3H), 1.45–1.32 (m,
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3H), 1.29–1.19 (m, 1H), 0.94 (t, J = 7.2 Hz); C{1H} NMR (151 MHz; CD3OD) δ 146.5, 146.1,
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128.9, 122.8, 116.2, 113.0, 60.9, 41.7, 39.0, 26.5, 26.4, 25.9, 23.9, 14.2; m/z [ES+] 236 ([MH]+,
100%); m/z [HRMS ES+] calcd for C14H22NO2 236.1648 [MH]+, found 236.1645.
1-(But-3-en-1-yl)-1-methyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol. (12.HCl)
Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (210.4 μL) in a capped Eppendorf tube. 5-
Hexen-2-one (289.6 μL, 2.50 mmol) was then added and the reaction mixture shaken under argon at
70 °C. After 20 h the NMR yield (60%) was determined following the general procedure described.
Two further duplicate reactions were performed, and the two reaction products combined and purified
using preparative HPLC method III. Fractions were combined, exchanged with HCl (1 M) and freeze
dried to give 12.HCl (5.4 mg, 41%) as a white solid. Mp. > 250 °C (H2O); nmax (film) 3196, 2957,
1672, 1616, 1369 cm–1; 1H NMR (600 MHz; CD3OD) δ 6.67 (s, 1H), 6.59 (s, 1H), 5.82 (dt, J = 16.9,
10.3 Hz, 1H), 5.09 (dd, J = 16.9, 1.5 Hz, 1H), 5.01 (br d, J = 10.3 Hz, 1H), 3.48–3.42 (m, 2H), 2.99–
2.96 (m, 1H), 2.95–2.89 (m, 1H), 2.24–2.15 (m, 1H), 2.08–2.01 (m, 3H), 1.67 (s, 3H); 13C{1H} NMR
(151 MHz; CD3OD) δ 146.6, 146.2, 137.9, 128.5, 122.9, 116.24, 116.18, 113.0, 60.8, 41.1, 39.1, 28.8,
26.4, 25.9; m/z [ES+] 234 ([MH]+, 100%); m/z [HRMS ES+] calcd for C14H20NO2 234.1489 [MH]+,
found 234.1490.
1-Methyl-1-phenyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride. (13.HCl)
To a solution of dopamine hydrochloride (95 mg, 0.50 mmol) and sodium ascorbate (100 mg, 0.50
mmol) in KPi buffer (0.3 M, pH 9, 5 mL) and methanol (2.08 mL) was added acetophenone (2.92
mL, 25 mmol). The reaction mixture was heated at 70 °C for 20 h and the methanol removed in vacuo.
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The product was extracted with ethyl acetate (3 × 15 mL) and the organic phases combined, dried,
and evaporated. The residue was suspended in dimethyl carbonate (10 mL) and HCl (10 mL, 1 M)
and the aqueous phase washed with dimethyl carbonate (3 × 5 mL) then evaporated to obtain the
crude product. This was dissolved in water-acetonitrile (1:1) and directly purified using preparative
HPLC method III. Fractions were combined, exchanged with HCl (1 M) and evaporated to give
13.HCl (6.0 mg, 4.1%) as a pale yellow solid. The NMR yield of the reaction (11%) was determined
following the general procedure described. Mp. > 200 °C decomposed (H2O); nmax (film) 3208, 2961,
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2783, 1585 cm–1; H NMR (600 MHz; CD3OD) δ 7.45–7.39 (m, 3H), 7.35–7.30 (m, 2H), 6.69 (s,
1H), 6.47 (s, 1H), 3.42–3.35 (m, 1H), 3.15–3.05 (m, 2H), 2.98–2.92 (m, 1H), 2.13 (s, 3H); 13C{1H}
NMR (151 MHz; CD3OD) δ 147.2, 146.2, 142.0, 130.4, 130.1, 129.1, 128.0, 123.9, 116.0, 114.6,
63.3, 39.1, 27.3, 25.8; m/z [ES+] 256 ([MH]+, 100%); m/z [HRMS ES+] calcd for C16H18NO2
256.1332 [MH]+, found 256.1332.
1-Benzyl-1-methyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride.19 (14.HCl)
To a solution of dopamine hydrochloride (56 mg, 0.30 mmol) and sodium ascorbate (60 mg, 0.30
mmol) in KPi buffer (0.3 M, pH 9, 10 mL) and methanol (10 mL) was added phenyl acetone (400
μL, 3.0 mmol). The reaction mixture was heated at 70 °C for 18 h and the methanol removed in vacuo.
The product was extracted with ethyl acetate (3 × 20 mL) and the organic phases combined, dried
and evaporated. The residue was resuspended in dimethyl carbonate (10 mL) and HCl (10 mL, 1 M)
and the aqueous phase washed with dimethyl carbonate (4 × 5 mL) then evaporated to obtain the
crude product. This was dissolved in water-acetonitrile (1:1) and was purified (twice) using
preparative HPLC method III. Fractions were combined, exchanged with HCl (1 M) and evaporated
to give 14.HCl (2.4 mg, 3%). The NMR yield of the reaction (25%) was determined following the
general procedure described. 1H NMR (700 MHz; CD3OD) δ 7.36–7.29 (m, 3H), 7.18–7.15 (m, 2H),
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6.63 (s, 1H), 6.60 (s, 1H), 3.36–3.32 (m, 3H), 3.25 (d, J = 14.0 Hz, 1H), 2.93 (t, J = 6.3 Hz, 2H), 1.67
(s, 3H); 13C{1H} NMR (176 MHz; CD3OD) δ 146.6, 145.8, 135.3, 131.8, 129.6, 128.7, 127.9, 122.9,
116.0, 113.5, 60.8, 47.1, 39.0, 26.5, 25.6; m/z [ES+] 270 ([MH]+, 100%).
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1-Ethyl-1-(trifluoromethyl)-1,2,3,4-tetrahydroisoquinoline-6,7-diol hydrochloride. (15.HCl)
To a solution of dopamine hydrochloride (19 mg, 0.10 mmol) and sodium ascorbate (20 mg, 0.10
mmol) in KPi buffer (0.3 M, pH 9, 1 mL) and methanol (0.32 mL) was added 1,1,1-trifluoro-2-
butanone (0.68 mL, 5.0 mmol). The reaction mixture was heated at 70 °C for 18 h and monitored by
analytical HPLC. The reaction mixture was directly purified using preparative HPLC method I.
Fractions were combined, exchanged with HCl (1 M) and evaporated to give 15.HCl (26 mg, 88%)
as a white solid. The NMR yield of the reaction (93%) was determined following the general
procedure described. Mp. 115-117 °C (H2O); nmax (film) 3130, 3042, 1526 cm–1; 1H NMR (600 MHz;
CD3OD) δ 6.81 (s, 1H), 6.70 (s, 1H), 3.60–3.45 (m, 2H), 3.04 (dt, J = 17.4, 6.3 Hz, 1H), 2.96 (dt, J
= 17.4, 6.0, 1H), 2.45–2.35 (m, 2H), 1.06 (t, J = 7.8 Hz, 3H); 13C{1H} NMR (151 MHz; CD3OD) δ
148.4, 146.6, 126.2 (1JCF = 285 Hz, CF3), 126.1, 117.4, 116.7, 113.9, 65.9 (2JCF = 26.7 Hz, CCF3),
41.6, 28.7, 25.6, 7.8; m/z [ES+] 262 ([MH]+, 100%); m/z [HRMS ES+] calcd for C12H15F3NO2
262.1049 [MH]+, found 262.1049.
3-Methyl-3',4'-dihydro-2'H-spiro[cyclohexane-1,1'-isoquinoline]-6',7'-diol
(16.HCl)
hydrochloride.19
Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (438.7 μL) in a capped Eppendorf tube. 3-
Methylcyclohexanone (61.3 μL, 0.50 mmol) was then added and the reaction mixture shaken under
argon at 70 °C. After 20 h the NMR yield (70%) was determined following the general procedure
described. Two further duplicate reactions were performed, and the two reaction products combined
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and purified using preparative HPLC method I. Fractions were combined, exchanged with HCl (1 M)
and freeze dried to give 16.HCl (8.7 mg, 61%) as a solid. Mp. > 250 °C (H2O); nmax (film) 3196, 2947,
1594, 1394 cm–1; 1H NMR (600 MHz; CD3OD) δ 6.73 (s, 1H), 6.57 (s, 1H), 3.42–3.39 (m, 2H), 2.96–
2.94 (m, 2H), 2.08–1.99 (m, 2H), 1.93 (td, J = 14.6, 4.4 Hz, 1H), 1.88–1.81 (m, 2H), 1.78–1.69 (m,
1H), 1.68–1.60 (m, 2H), 1.13 (dq, J = 12.6, 4.2 Hz, 1H), 1.00 (d, J = 6.3 Hz, 3H); 13C{1H} NMR (151
MHz; CD3OD) δ 146.5, 146.1, 129.6, 123.0, 116.1, 113.2, 61.7, 45.3, 38.7, 36.3, 34.1, 28.3, 26.2,
22.5, 21.6; m/z [HRMS ES+] calcd for C15H22NO2 248.1651 [MH]+, found 248.1664.
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4-Methyl-3',4'-dihydro-2'H-spiro[cyclohexane-1,1'-isoquinoline]-6',7'-diol
(17.HCl)
hydrochloride.19
Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (438.7 μL) in a capped Eppendorf tube. 4-
Methylcyclohexanone (61.3 μL, 0.50 mmol) was then added and the reaction mixture shaken under
argon at 70 °C. After 20 h the NMR yield (80%) was determined following the general procedure
described. Two further duplicate reactions were performed, and the two reaction products combined
and purified using preparative HPLC method I. Fractions were combined, exchanged with HCl (1 M)
and freeze dried to give 17.HCl (9.5 mg, 67%) as a solid. Mp. > 250 °C (H2O); nmax (film) 3196, 2947,
1594, 1394 cm–1; 1H NMR (600 MHz; CD3OD) δ 6.73 (s, 1H), 6.57 (s, 1H), 3.41 (t, J = 6.4 Hz, 2H),
2.95 (t, J = 6.4 Hz, 2H), 2.10–2.05 (m, 4H), 1.78 (dd, J = 15.0, 1.8 Hz, 2H), 1.69–1.60 (m, 1H), 1.36–
1.22 (m, 2H), 1.03 (d, J = 6.5 Hz, 3H); C{1H} NMR (151 MHz; CD3OD) δ 146.5, 146.1, 129.5,
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123.2, 116.1, 113.2, 60.6, 38.7, 36.9, 32.4, 30.1, 26.2, 22.2; m/z [HRMS ES+] calcd for C15H22NO2
248.1651 [MH]+, found 248.1661.
4-Isopropyl-3',4'-dihydro-2'H-spiro[cyclohexane-1,1'-isoquinoline]-6',7'-diol hydrochloride.
(18.HCl)
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Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (463 μL) in a capped Eppendorf tube. 4-
Isopropylcyclohexanone (70 mg, 0.50 mmol) was then added and the reaction mixture shaken under
argon at 70 °C. After 20 h the NMR yield (75%) was determined following the general procedure
described. Two further duplicate reactions were performed, and the two reaction products combined
and purified using preparative HPLC method III. Fractions were combined, exchanged with HCl (1
M) and freeze dried to give 18.HCl (8.3 mg, 53%) as a white solid. Mp. > 250 °C (H2O); nmax (film)
3223, 2931, 1652, 1524 cm–1; 1H NMR (600 MHz; CD3OD) δ 6.73 (s, 1H), 6.57 (s, 1H), 3.41 (t, J =
6.4 Hz, 2H), 2.95 (t, J = 6.4 Hz, 2H), 2.08 (m, 4H), 1.91–1.84 (m, 2H), 1.57–1.48 (m, 1H), 1.34–1.25
(m, 3H), 0.97 (d, J = 6.8 Hz, 6H); 13C NMR (151 MHz; CD3OD) δ 146.5, 146.1, 129.5, 123.2, 116.1,
113.2, 60.9, 44.1, 38.8, 37.2, 33.9, 26.3, 25.5, 20.3; m/z [ES+] 276 ([MH]+, 100%); m/z [HRMS ES+]
calcd for C17H26NO2 276.1958 [MH]+, found 276.1960.
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2',3,3',4,5',6'-Hexahydro-2H-spiro[isoquinoline-1,4'-pyran]-6,7-diol hydrochloride. (19.HCl)
Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (453.8 μL) in a capped Eppendorf tube.
Tetrahydro-4H-pyran-4-one (46.2 μL, 0.50 mmol) was then added and the reaction mixture shaken
under argon at 70 °C. After 20 h the NMR yield (83%) was determined following the general
procedure described. Two further duplicate reactions were performed, and the two reaction products
combined and purified using preparative HPLC method III. Fractions were combined, exchanged
with HCl (1 M) and freeze dried to give 19.HCl (8.9 mg, 65%) as a white solid. Mp. 200 °C
decomposed (H2O); nmax (film) 3223, 2969, 1591, 1525 cm–1; 1H NMR (600 MHz; CD3OD) δ 6.79 (s,
1H), 6.59 (s, 1H), 3.97 (dd, J = 12.6, 4.5 Hz, 2H), 3.76 (td, J = 12.6, 2.0 Hz, 2H), 3.48 (t, J = 6.4 Hz,
2H), 2.98 (t, J = 6.4 Hz, 2H), 2.35 (ddd, J = 15.4, 12.6, 4.5 Hz, 2H), 2.00 (m, 2H); C{1H} NMR
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(151 MHz; CD3OD) δ 146.9, 146.3, 128.5, 123.4, 116.2, 113.4, 63.3, 58.7, 39.0, 36.8, 26.1; m/z [ES+]
236 ([MH]+, 100%); m/z [HRMS ES+] calcd for C13H18NO3 236.1281 [MH]+, found 236.1282.
3',4'-Dihydro-2'H-spiro[cyclobutane-1,1'-isoquinoline]-6',7'-diol hydrochloride. (20.HCl)
Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (463 μL) in a capped Eppendorf tube.
Cyclobutanone (37 μL, 0.50 mmol) was then added and the reaction mixture shaken under argon at
70 °C. After 20 h the NMR yield (97%) was determined following the general procedure described.
Two further duplicate reactions were performed, and the two reaction products combined and purified
using preparative HPLC method III. Fractions were combined, exchanged with HCl (1 M) and freeze
dried to give 20.HCl (8.9 mg, 74%) as a white solid. The reaction was scaled-up using 5.HCl (1.00
g, 5.27 mmol) sodium ascorbate (1 equiv. with respect to dopamine) in KPi buffer (0.3 M, pH 9, 52.7
mL) and methanol (52.7 mL), and cyclobutanone was added (3.92 mL, 52.7 mmol). The reaction
mixture was shaken at 70 °C for 20 h, then the pH adjusted to 3 by the addition of HCl (2 M). The
solvent was removed in vacuo, and the residue suspended in acetonitrile at 0 ºC. Finally, the mixture
was filtered and solvent removed in vacuo to give 20.HCl (0.646 g, 51%). Mp. > 250 °C (H2O); nmax
(film) 3155, 2947, 1578, 1398 cm–1; 1H NMR (600 MHz; CD3OD) δ 7.03 (s, 1H), 6.57 (s, 1H), 3.36
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(t, J = 6.4 Hz, 2H), 2.93 (t, J = 6.4 Hz, 2H), 2.59 (t, J = 8.3 Hz, 4H), 2.22 (m, 2H); C{1H} NMR
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(151 MHz; CD3OD) δ 146.9, 146.4, 128.5, 122.8, 115.8, 112.4, 61.3, 39.5, 35.1, 26.1, 14.2; m/z [ES+]
206 ([MH]+, 100%); m/z [HRMS ES+] calcd for C12H16NO2 206.1176 [MH]+, found 206.1176.
3',4'-Dihydro-2'H-spiro[cyclopentane-1,1'-isoquinoline]-6',7'-diol hydrochloride. (21.HCl)
Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10 mg, 0.050 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (456 μL) in a capped Eppendorf tube.
Cyclopentanone (44 μL, 0.50 mmol) was then added and the reaction mixture shaken under argon at
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70 °C. After 20 h the NMR yield (95%) was determined following the general procedure described.
Two further duplicate reactions were performed, and the two reaction products combined and purified
using preparative HPLC method III. Fractions were combined, exchanged with HCl (1 M) and freeze
dried to give 21.HCl (9.8 mg, 77%) as a solid. Mp. >200 °C decomposed (H2O); nmax (film) 3223,
2970, 1592 cm–1; 1H NMR (600 MHz; CD3OD) δ 6.66 (s, 1H), 6.55 (s, 1H), 3.42 (t, J = 6.4 Hz, 2H),
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2.95 (t, J = 6.4 Hz, 2H), 2.24–2.12 (m, 4H), 2.0 –1.98 (m, 2H), 1.98–1.90 (m, 2H); C{1H} NMR
13
(151 MHz; CD3OD) δ 146.5, 146.3, 129.6, 123.1, 115.8, 112.8, 68.8, 42.0, 40.3, 26.0, 25.9; m/z [ES+]
220 ([MH]+, 100%); m/z [HRMS ES+] calcd for C13H18NO2 220.1332 [MH]+, found 220.1329.
1,3,3',4'-Tetrahydro-2'H-spiro[indene-2,1'-isoquinoline]-6',7'-diol hydrochloride. (22.HCl)
Dopamine hydrochloride (56 mg, 0.30 mmol), sodium ascorbate (60 mg, 0.30 mmol), and 2-
indanone (396 mg, 3.0 mmol) were mixed in KPi buffer (0.3 M, pH 9, 10 mL) and methanol (10 mL)
The reaction mixture was stirred at 70 °C for 18 h, and then diluted to 50 mL with water. The brown
insoluble precipitate was removed by filtration and the filtrate extracted with ethyl acetate (4 × 20
mL). The organic phase was washed with brine (2 × 20 mL), dried, filtered and evaporated to obtain
the crude product. The residue was washed with cold ethanol, stirred in HCl (1 M) for 4 h and the
solvent removed in vacuo (< 55 °C) to give 22.HCl (38 mg, 57%) as a white solid. The NMR yield
(70%) was determined following the general procedure described. Mp. >240 °C decomposed (H2O);
n
max (film) 3396 (br), 1621, 1590, 1524 cm–1; 1H NMR (600 MHz; CD3OD) δ 7.35–7.27 (m, 4H), 6.60
(s, 1H), 6.56 (s, 1H), 3.60 (d, J = 17.1 Hz, 2H), 3.56 (d, J = 17.1 Hz, 2H), 3.51 (t, J = 6.6 Hz, 2H),
3.03 (t, J = 6.6 Hz, 2H); C{1H} NMR (151 MHz; CD3OD) δ 147.0, 146.3, 140.0, 129.1, 128.9,
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125.9, 122.9, 116.0, 112.1, 67.8, 48.1, 40.5, 26.0; m/z [ES+] 268 ([MH]+, 100%); m/z [HRMS ES+]
calcd for C17H18NO2 268.1332 [MH]+, found 268.1332.
2,3,3',4'-Tetrahydro-2'H-spiro[indene-1,1'-isoquinoline]-6',7'-diol hydrochloride. (23.HCl)
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Dopamine hydrochloride (9.5 mg, 0.050 mmol), sodium ascorbate (10 mg, 0.050 mmol) and 1-
indanone (66 mg, 0.5 mmol) were mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (500 μL)
in a capped Eppendorf tube. The reaction mixture was shaken under argon at 70 °C. After 20 h the
NMR yield (21%) was determined following the general procedure described. Two further duplicate
reactions were performed, and the two reaction products combined and purified using preparative
HPLC method I. Fractions were combined, exchanged with HCl (1 M) and solvent removed in vacuo
(< 55 °C) to give 23.HCl (2.1 mg, 7%) as a white solid. Mp. > 240 °C decomposed (H2O); nmax (film)
3142, 2946, 2791, 1605, 1408 cm–1; 1H NMR (700 MHz; CD3OD) δ 7.48–7.42 (m, 2H), 7.32 (t, J =
7.0 Hz, 1H), 7.14 (d, J = 7.0 Hz, 1H), 6.66 (s, 1H), 6.16 (s, 1H), 3.60–3.48 (m, 2H), 3.30–3.24 (m,
1H), 3.23–3.14 (m, 2H), 3.02 (dt, J = 16.8, 4.2 Hz, 1H), 2.81–2.72 (m, 1H), 2.60 (dt, J = 16.8, 8.4
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Hz, 1H); C NMR (176 MHz; CD3OD) δ 146.9, 146.0, 145.9, 143.5, 131.3, 128.6, 127.6, 126.40,
126.36, 123.8, 115.5, 114.2, 71.8, 41.0, 40.0, 30.1, 25.6; m/z [ES+] 268 ([MH]+, 100%); m/z [HRMS
ES+] calcd for C17H18NO2 268.1332 [MH]+, found 268.1331.
3',4'-Dihydro-2'H-spiro[cyclohexane-1,1'-isoquinolin]-6'-ol hydrochloride.10 (24.HCl)
2-(3-Hydroxyphenyl)ethylamine hydrochloride20 (8.7 mg, 0.050 mmol), and sodium ascorbate (10
mg, 0.050 mmol) were mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (241 μL) in a capped
Eppendorf tube. Cyclohexanone (259 μL, 2.5 mmol) was added and the mixture shaken under argon
at 70 °C. After 20 h the NMR yield (74%) was determined following the general procedure described.
Two further duplicate reactions were performed, and the two reaction products combined and then
purified using preparative HPLC method I. Fractions were combined, exchanged with HCl (1 M) and
the solvent removed in vacuo (< 55 °C) to give 24.HCl (7.1 mg, 55%) as a solid. Mp. > 250 °C (H2O);
n
max (film) 3217, 2930, 2766, 1589, 1440 cm–1; 1H NMR (700 MHz; CD3OD) δ 7.24 (d, J = 7.8 Hz,
1H), 6.74 (dd, J = 7.8, 2.1 Hz, 1H), 6.60 (d, J = 2.1 Hz, 1H), 3.45 (t, J = 6.3 Hz, 2H), 3.06 (t, J = 6.3
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Hz, 2H), 2.09–2.03 (m, 4H), 1.87–1.79 (m, 3H), 1.70–1.62 (m, 2H), 1.55–1.45 (m, 1H); C{1H}
NMR (176 MHz; CD3OD) δ 157.8, 133.1, 129.5, 128.1, 115.9, 115.7, 61.0, 38.2, 36.6, 26.7, 25.0,
21.5; m/z [ES+] 218 ([MH]+, 100%); m/z [HRMS ES+] calcd for C14H20NO 218.1539 [MH]+, found
218.1539.
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7'-Fluoro-3',4'-dihydro-2'H-spiro[cyclohexane-1,1'-isoquinolin]-6'-ol hydrochloride. (25.HCl)
To a solution of 2-(4-fluoro-3-hydroxyphenyl)ethylamine hydrobromide20 (23.6 mg, 0.10 mmol)
and sodium ascorbate (20 mg, 0.10 mmol) in KPi buffer (0.3 M, pH 9, 1 mL) and methanol (0.32
mL) cyclohexanone (518 μL, 5.0 mmol) was added. The reaction mixture was heated at 70 °C for 20
h and the methanol was removed in vacuo. The solution was freeze-dried, dissolved in water-
acetonitrile (1:1) and centrifuged at 4000 rpm for 10 min. The supernatant was then purified by
preparative HPLC method I. Fractions were combined, exchanged with HCl (1 M) and evaporated
(at < 55 °C) to give 25.HCl (14 mg, 50%) as a white solid. The NMR yield of the reaction (55%) was
determined following the general procedure described. Mp. > 250 °C (H2O); nmax (film) 3150, 3061,
2942, 2762, 1525 cm–1; 1H NMR (600 MHz; CD3OD) δ 7.18 (d, 3JHF = 12.6 Hz, 1H), 6.74 (d, 4JHF =
8.4 Hz, 1H), 3.45 (t, J = 6.2 Hz, 2H), 3.03 (t, J = 6.2 Hz, 2H), 2.11–1.97 (m, 4H), 1.89–1.74 (m, 3H),
13
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1.73–1.59 (m, 2H), 1.56–1.42 (m, 1H); C{1H} NMR (151 MHz; CD3OD) δ 152.1 (d, JCF = 241
Hz), 145.9 (d, 2JCF = 13.4 Hz), 130.3, 128.4, 118.6 (d, JCF = 3.0 Hz), 114.4 (d, JCF = 21.0 Hz), 61.0,
38.4, 36.6, 26.3, 25.1, 21.6; m/z [ES+] 236 ([MH]+, 100%); m/z [HRMS ES+] calcd for C14H19FNO
236.1445 [MH]+, found 236.1446.
5-(2-Aminoethyl)benzene-1,3-diol hydrobromide.36
The reaction was carried out in anhydrous condition. To a solution of 3,5-dimethoxyphenyl
acetonitrile (753 mg, 4.25 mmol) in THF (10 mL) was added borane-THF solution (1 M; 13 mL, 13
mmol) at 0 °C. The reaction was stirred for 24 h at room temperature, cooled to 0 °C and methanol
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(30 mL) was added. The solution was then stirred for another 24 h, concentrated under vacuum and
co-evaporated with methanol (3 × 10 mL). The residue was purified by silica column chromatography
(dichloromethane-methanol (containing 1% triethylamine), 9:1 to 5:1) to give 2-(3,5-
dimethoxyphenyl)ethan-1-amine37 (427 mg, 55%) as an oil. Rf = 0.13 (dichloromethane-methanol
(containing 1% triethylamine), 9:1); 1H NMR (600 MHz; CDCl3) δ 6.36–6.34 (m, 2H), 6.32 (t, J =
2.4 Hz, 1H), 3.77 (s, 6H), 2.96 (t, J = 7.2 Hz, 2H), 2.70 (t, J = 7.2 Hz, 2H), 2.12 (br s, 2H); 13C{1H}
NMR (151 MHz; CDCl3) δ 161.0, 142.1, 107.0, 98.2, 55.4, 43.2, 40.0.
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2-(3,5-Dimethoxyphenyl)ethan-1-amine (427 mg, 2.36 mmol) was stirred in dichloromethane (20
mL) and boron tribromide (1 M; 7.5 mL, 7.5 mmol) at room temperature for 24 h. Methanol (30 mL)
was then added and the reaction stirred for another 3 h. The mixture was then concentrated under the
vacuum and co-evaporated with methanol to give 5-(2-aminoethyl)benzene-1,3-diol.HBr36 (572 mg,
100%) as the HBr salt. 1H NMR (600 MHz; CD3OD) δ 6.23 (d, J = 2.3 Hz, 2H), 6.19 (t, J = 2.3 Hz,
1H), 3.14 (t, J = 7.8 Hz, 2H), 2.82 (t, J = 7.8 Hz, 2H); 13C{1H} NMR (151 MHz; CD3OD) δ 160.0,
140.0, 108.2, 102.5, 41.9, 34.5; m/z [ES+] 154 ([MH]+, 100%).
3',4'-Dihydro-2'H-spiro[cyclohexane-1,1'-isoquinoline]-6',8'-diol hydrochloride. (26.HCl)
3,5-Dihydroxyl phenethylamine hydrobromide (11.7 mg, 0.050 mmol),and sodium ascorbate (10
mg, 0.050 mmol) were mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (241 μL) in a capped
Eppendorf tube. Cyclohexanone (259 μL, 2.5 mmol) was added and the mixture shaken under argon
at 70 °C. After 20 h the NMR yield (57%) was determined following the general procedure described.
Two further duplicate reactions were performed, and the two reaction products combined and then
purified using preparative HPLC method I. Fractions were combined, exchanged with HCl (1 M) and
the solvent removed in vacuo (< 55 °C) to give 26.HCl (5.0 mg, 37%) as a solid. Mp. > 250 °C (H2O);
nmax (film) 3232, 3092, 2861, 1590 cm–1; 1H NMR (600 MHz; CD3OD) δ 6.23 (d, J = 2.4 Hz, 1H),
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6.14 (d, J = 2.4 Hz, 1H), 3.34 (t, J = 6.0 Hz, 2H), 3.04–2.95 (m, 4H), 1.82–1.73 (m, 5H), 1.67–1.53
(m, 2H), 1.50–1.34 (m, 1H); 13C{1H} NMR (151 MHz; CD3OD) δ 158.7, 157.1, 134.9, 116.1, 108.1,
103.8, 61.6, 38.3, 31.8, 28.0, 25.1, 21.6; m/z [ES+] 256 ([MNa]+, 29%), 234 ([MH]+, 75); m/z [HRMS
ES+] calcd for C14H20NO2 234.1489 [MH]+, found 234.1489.
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8,9-Dihydroxy-10b-methyl-1,5,6,10b-tetrahydropyrrolo[2,1-a]isoquinolin-3(2H)-one. (29)
Dopamine hydrochloride (9.5 mg, 0.050 mmol) and sodium ascorbate (10.5 mg, 0.053 mmol) were
mixed in KPi buffer (0.3 M, pH 9, 500 μL) and methanol (200 μL) in a capped Eppendorf tube.
Methyl levulinate 28 (300 μL, 2.5 mmol) was added and the mixture shaken under argon at 70 °C for
20 h. A duplicate reaction was performed, these two reactions were combined and the methanol
removed in vacuo. The solution was freeze-dried and the NMR yield of the reaction (50%) determined
following the general procedure described. The product was then purified using preparative HPLC
method I. Fractions were combined, exchanged with HCl (1 M) and the solvent removed in vacuo (<
55 °C) to give 29.HCl (4.4 mg, 19%) as a white solid. Mp. > 237-238 °C (H2O); nmax (film) 3246 (br),
2966, 1644, 1520 cm–1; 1H NMR (700 MHz; CD3OD) δ 6.57 (s, 1H), 6.50 (s, 1H), 4.12 (dd, J = 13.3,
6.3 Hz, 1H), 3.11 (td, J = 13.3, 4.7 Hz, 1H), 2.75–2.69 (m, 1H), 2.67–2.60 (m, 2H), 2.41–2.33 (m,
2H), 2.06–2.00 (m, 1H), 1.49 (s, 3H); C{1H} NMR (176 MHz; CD3OD) δ 174.8, 145.4, 145.2,
13
134.9, 124.1, 116.0, 112.4, 62.8, 35.7, 35.4, 31.4, 28.6, 27.2; m/z [ES+] 234 ([MH]+, 100%); m/z
[HRMS ES+] calcd for C13H16NO3 234.1125 [MH]+, found 234.1126.
ASSOCIATED CONTENT
Supporting Information
The supporting information is available free of charge on the ACS Publications website at DOI: xxxx.
Supplementary Figures and Tables and 1H NMR and 13C NMR spectra of all new products.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: h.c.hailes@ucl.ac.uk
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H. C. Hailes: 0000-0001-5574-4742
J. M. Ward: 0000-0002-4415-5544
Notes
The authors declare no competing financial interests.
ACKNOWLEDGEMENTS
We gratefully acknowledge UCL Dean’s Prize and UCL-China Scholarship Council Joint Research
Scholarship for funding Jianxiong Zhao and the Biotechnology and Biosciences Research Council
(BBRSC) (BB/N01877X/1) for funding Daniel Méndez Sánchez. We also thank Yu Wang, K. Karu
(UCL Mass Spectrometry Facility) and A. E. Aliev (UCL NMR Facility) in the Department of
Chemistry.
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