Deciphering the conformation of C-linked α-D-mannopyranosides and their application toward the synthesis of low nanomolar E. Coli FimH ligands

Article abstract of DOI:10.24820/ark.5550190.p010.783

C-Allyl –D-mannopyranosides were prepared via a variety of routes to determine an optimal route to the - anomers. The relative conformational energies of the key intermediate was evaluated by molecular modeling which showed the conventional⁴C

Full text of DOI:10.24820/ark.5550190.p010.783

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Deciphering the conformation of C-linked α-D-mannopyranosides and their
application toward the synthesis of low nanomolar E. coli FimH ligands
Leila Mousavifar, *a,b Gérard Vergoten,c and René Roy*a,b,d
a Department of Chemistry, Université du Québec à Montréal, P.O. Box 8888, Succ. Centre-Ville, Montréal,
Québec H3C 3P8, Canada
b INRS-Institut Armand-Frappier, Université du Québec, 531 boul. des Prairies, Laval, Québec, H7V 1B7, Canada
c Unité de Glycobiologie Structurale et Fonctionnelle (UGSF), UMR8576 du CNRS, Université de Lille, F-59000
Lille, France
d Glycovax Pharma Inc., 424 Guy, Suite 202, Montreal, Quebec, Canada, H3J 1S6
E-mail: leilyanmousavifar@gmail.com; rroy@glycovax.com
Received 10-12-2018
Accepted 11-22-2018
Published on line 11-28-2018
Abstract
C-Allyl –D-mannopyranosides were prepared via a variety of routes to determine an optimal route to the -
anomers. The relative conformational energies of the key intermediate was evaluated by molecular modeling
4
which showed the conventional C1 chair conformation to be the lowest energy conformer. This finding was
also confirmed by NMR and X-ray crystallography. The perbenzoylated C-allyl mannoside was also converted
into 1,1’-biphenyl analogues using a palladium-catalyzed Heck reaction. Two of the resulting minor reaction
products were co-crystallized with the uropathogenic E. coli FimH. Alternatively, the KD of the major and
expected Heck product was in the low nM range as measured by SPR. Crystal data showed that the C-linked
derivatives efficiently bind in the FimH binding cavity near the so-called hydrophobic tyrosine gate.
Keywords: E. coli FimH, mannoside, Heck reaction, molecular modeling, X-ray
DOI: https://doi.org/10.24820/ark.5550190.p010.783
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Introduction
Adherent-invasive Escherichia coli (AIEC) infections are a serious health problem for which alternative
therapeutic strategies are very timely,1,2 particularly in light of bacterial resistance against the most recent
arsenal of antibacterial agents.3-5 Amongst these, Escherichia coli responsible of urinary tract infections (UTIs),
intestinal bowel diseases (IBDs) such as Crohns’s disease (CD), and ulcerative colitis constitute major
challenges for medicinal chemistry.6,7 Uropathogenic E. coli infections (UPECs) affect 50% of women at least
once in their life-times. The premises to infections result from the crucial contacts between the bacterial
carbohydrates binding proteins type 1 fimbriae (FimH) and PapG which bind uroplakin Ia glycoprotein and
glycolipids, respectively. E. coli type FimH has hair-like appendages on the bacterial cell surface which
constitute key virulence factors. They are responsible for the initial adhesion to mucosal surfaces via
interaction with multiantennary mannosylated receptors.7 Bacterial adhesion to host cells is a preliminary step
toward the release of toxic proteins, therefore the design of E. coli FimH antagonists (antiadhesins) has been
the target of several efforts from the glycobiology community.7–25
Even though several families of potent α-D-mannopyranoside-based antiadhesins have been synthesized
that included polymers,26-28 dendrimers,29-30 gold nanoparticles,31 and dendrimersomes,32 small molecule
antagonists still represent the foremost choice of the pharmaceutical industry. Glycomimetics are the most
promising candidates for the replacement of naturally occurring complex oligomannosides with C-linked
glycosyl derivatives being the preferred options.1,11 However, in the case of C-linked mannopyranosides and
those possessing hydrophobic/aryl aglycones in particular, there have been very few studies on their precise
conformational analyses.33 This is particularly important given the propensity of C-mannopyranosides to exist
in diverse conformations (4C1, 1C4, 2S0, and 0S2).34-38
This paper describes practical approaches to the syntheses of C-allyl α-D-mannopyranoside, which is a
versatile building block toward E. coli FimH antagonists. Molecular modeling, X-ray crystallography, and
4
binding studies support that C-allyl α-D-mannopyranosides exist in the required and most stable C1
conformation and that the corresponding 1,1’-biphenyl derivatives, obtained through palladium-catalyzed
Heck cross-coupling, represent hydrolytically stable and promising leads as E. coli FimH antagonists.
Results and Discussion
In conventional drug design, O-linked glycomimetics should be largely avoided due to their propensity to
readily hydrolyze in in vivo settings. To avoid this problem, C-linked α-D-mannopyranosides attached to alkene
chains were investigated.1,11 Diversely protected C-allyl α-D-mannopyranosides are useful intermediates for
the synthesis of this important family of glycomimetics. Conventional routes for their syntheses are illustrated
in Scheme 1. So far, in its most α-stereoselective approach, it was obtained from the known perbenzylated
methyl α-D-mannopyranoside 1,39 which under Sakurai reaction39,40 (BF3·OEt2, allyltrimethylsilane) provided 2
in more than 95% of its α-anomer (Scheme 1). Unfortunately, benzyl protecting groups have some drawbacks
for their forthcoming palladium-catalyzed Heck coupling and hydrogenolysis deprotection.11 Alternatively,
Birch reduction of 2 and acetylation affords the more versatile peracetylated analogue 3α in good overall
yield, albeit in three consecutive steps. Disappointingly, application of the Sakurai conditions, directly on
peracetylated mannose 6α,β afforded an intractable mixture of 3α and 3β.41 This result prompted us to
attempt the reaction on a anomeric mixture of the known perbenzoylated mannopyranose 4α/4β.42
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Scheme 1. Synthesis of C-allyl α-D-mannopyranosides under Sakurai condition with different protecting groups
(see Table 1).
Delightfully, in contrast to the peracetylated analogue 6,41 the Sakurai products 5α and 5β resulting from
the perbenzoylated mixture 4α/4β were separable, but with reduced α-stereoselectivity (7:1) when compared
to the perbenzylated derivative 1 (15α:1β). As anticipated, during the course of this transformation, we also
observed that 4α reacted faster than its β-anomer 4β. Given that 4α and 4β were also separable,42 we
repeated the reaction on each separated isomer: the 4α anomer was completely converted to 5α/5β (1.7:1)
within 2 h while the 4β anomer provided 5α/5β more slowly but with an improved 4:1 anomeric
stereoselectivity. The fact that the above three conditions gave different anomeric stereoselectivities was not
surprising given the individual propensity of the precursors (α vs β) to react with the Lewis acid competitively.
To simplify access to a suitable and versatile starting material, we attempted the Sakurai reaction directly
from the commercially available methyl α-D-mannopyranoside 7 using previously described conditions (BTSFA,
AllylTMS, TMSOTf, MeCN, 0 °C,16 h).43,44 Although both the yield and the anomeric diastereoselectivity toward
unprotected 8α,β in one single step from 7 was acceptable, the anomeric mixture was not readily separable.
The comparative data for the above sets of transformations are illustrated in Table 1. With this information in
hand and for practical reasons, it was decided to pursue our goals using the perbenzoylated precursors 4α,β.
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Table 1. Synthesis and diastereoselectivity of C-allyl α-D-mannopyranosides using different methods
Starting
Material
Reaction
Conditions
Product
Yield
(%)
Ratioa
α : β
AllylTMS, TMSOTf
MeCN, 0 °C, 16 h
90
15:1:
4:1
2
1
AllylTMS, BF3·OEt2
DCE, 50 °C, 16 h
85
80
85
6
4
3
5
8
AllylTMS, BF3·OEt2
DCE, 50 °C, 16 h
7:1
9:1
BTSFA, AllylTMS, TMSOTf
MeCN, 0 °C, 16 h
7
a Ratios were obtained from the crude 1H NMR data.
As stated above,33-38 there are several papers indicating that C-linked α-D-mannopyranosides can exist in
4
conformations other than those observed for the corresponding O-linked derivatives, normally seen as C1
conformers. Obviously, changing bond lengths, bond angles, torsion angles, and conformations would have a
detrimental effect upon binding of antagonists to E. coli FimH. Given the importance of our key precursor, C-
allyl α-D-mannopyranoside 8α, we measured the energy levels of its various conformations in the gas phase.
4
1
2
0
The geometry optimizations of the C1, C4, S0 and S2 conformers were performed using density functional
theory (DFT) with the hybrid functional B3LYP and 6-31G* basis set. For that purpose, the Firefly45 and
GaussSum46 computer programs were used. Figure 1 clearly showed that the C1 conformer was more stable
4
than its 1C4 conformational isomer by at least 8.10 kcal/mol. In addition, the respective skew boats S0 and 0S2
2
4
conformers were 11.72 and 16.42 kcal/mol, respectively higher than that of the C1 conformer. These results
agreed with the solution phase data obtained from high field 1H NMR (900 MHz)11 coupling constants and nOe
experiments (see below). Solid phase X-ray data also strongly supported these results.
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Figure 1. Relative energy level of C-allyl α-D-mannopyranoside (8α) conformers.
NOESY NMR at 600 MHz helped us to demonstrate the solution conformation of C-allyl 2,3,4,6-tetra-O-
benzoyl-α-D-mannopyranoside (5α) (Figure 2). In addition to the expected correlation between H1 and H1’a
and H1’b, we observed a strong nOe between H1’b and H3 and H5, further confirming that even in the fully
4
protected forms the C-linked mannopyranoside existed in the suitable C1 conformation. Importantly, the
coupling constants for the H4 signal at δH 6.02 (dd, 1H, J3,4 = J4,5 = 9 Hz, H-4) clearly indicated a trans-diaxial
relationship between H4 and both H3 and H5. Moreover, a crystal structure of 5α showed it existed in the same
4C1 conformation. Overall, the data on both fully protected as well as unprotected analogues supported that
this family of C-linked mannopyranosides existed in the desired 4C1 conformation (Figure 3).
Figure 2. 1H NMR (CDCl3, 600 MHz) of perbenzoylated C-allyl α-D-mannopyranoside 5α.
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Figure 3. Left panel: conformational studies of C-allyl 2,3,4,6-tetra-O-benzoyl-α-D-mannopyranoside (5α) in
solution by nOe 1H NMR; right panel: ORTEP diagram for the X-ray structure of 5α.
4
Having secured the accurate C1 conformation of these valuable anomeric precursors (4α and 5α) in the
gas phase, solution, and solid-state (X-ray) (Figure 3), we pursued our goals toward potent E. coli FimH
antagonists capable of adequately placing hydrophobic pharmacophores within the FimH tyrosine gate
(Tyr48/Tyr137). Our hope was to bring anomeric aromatic substituents properly oriented and at proper
distances from these two hydrophobic aromatic amino acids for appropriate π-π stacking (or CH-π stacking),
known to greatly improve the binding affinities of FimH ligands.10-15 To this end, we opted for an elongation of
the aglycone side chain using palladium-catalyzed Heck cross coupling between allylic 5α and aryl iodide such
as 4-iodo-1,1’-biphenyl.
Somewhat surprisingly, when allylic α-D-mannopyranoside 5α was treated under our optimized conditions
(4-iodo-1,1’-biphenyl, Pd(OAc)2, TBAB, NaHCO3, DMF, 85 °C, 12 h),1,11 compound 9 was obtained as a major
product (93%) together with traces amount of stereo- and regio-isomers 11 and 13 (Scheme 2). The mixture of
1
side products (11 and 13) was clearly visible from the H NMR spectra of the crude reaction mixture. Their
formation has been previously explained when considering the reaction mechanism of the Heck reaction.1
After isolation of pure 9 (Scheme 2) and 11/13 mixture, they were separately submitted to de-O-benzoylation
(1 M NH3, MeOH, r.t., 36 h) to afford pure 10 (Figure 4) and an intractable mixture of 12/14. These two side
products could not be readily purified and fully characterized. Nevertheless, their mixture was submitted to
co-crystallization with E. coli FimH together with the major product. Even though we could not obtain X-ray
data from the complex of FimH and major product 10, both side products were individually and successfully
co-crystallized with the FimH47 in the open and closed tyrosine gate, respectively, thus establishing their exact
structures (Figure 5).
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Scheme 2. Heck cross-coupling reactions between 5α and 4-iodo-1,1’-biphenyl that afforded three
regio/stereoisomers 9,11 and 13.
1
A high field H NMR spectrum of deprotected 10 (major product) was fully assigned (Figure 4). The
chemical shifts and the coupling constants of the sugar ring protons, together with those of the aglycone were
in agreement with derivative 10 being in its expected 4C1 chair conformation.
Figure 4. 1H NMR (MeOH, 600 MHz) and 13C NMR of compound 10.
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Figure 5. E. coli FimH complexed with side products 12 (green) bound in the open Tyr gate (Tyr48-Tyr137,
protein pink, PDB: 5aal) and 14 (brown) in the closed tyrosine gate (protein yellow, PDB:5aap).47
We next undertook affinity measurements between FimH and compound 10 by surface plasmon
resonance (SPR).11 Compound 10, having its second phenyl group in the para-position, was a potent ligand (Kd
17 nM) but it was less potent than the recently identified ortho-substituted analogue 1511 having an almost 3-
fold affinity enhancement (Kd 6.9 nM). As opposed to the two side products 12 and 14, both compounds could
not be co-crystallized with FimH. However, based on previous work,11 docking of its lowest energy conformer,
obtained through modeling and high field NMR spectra, with the FimH adhesin indicated that the ortho-
substituted phenyl ring of 15 was able to interact with an additional amino acid isoleucine-13 (Ile13), located
in the clamp loop, thus opening the route for further lead improvement.
Figure 6. Comparison between para-substituted biphenyl 10 (Kd 17 nM) and ortho-substituted biphenyl 15 (Kd
6.9 nM); docking of the lowest energy conformer of 15 in the active site of FimH indicated additional
hydrophobic interactions with Ile13 (centroid with the ortho-phenyl at 4.8 Å).
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Conclusions
Several approaches to an important key intermediate for the synthesis of families of C-linked α-D-
mannopyranosides have been presented. Although some were more α-stereoselective than others, we opted
for the use of perbenzoylated precursors for practical reasons. Using optimized Sakurai allylation, good yields
4
of the C-allylated glycosyl derivatives were obtained. We demonstrated that these existed in the required C1
conformation, in the gas phase, solutions, and in the solid-state, as requested for efficient binding interactions
with one of the essential E.coli virulence factor FimH. We then explored the formation of the typical, as well as
of side products, obtained during the course of our palladium-catalyzed Heck cross-coupling reaction with a
key aryl iodide (4-iodo-1,1’-biphenyl). Even though, an X-ray complex between the FimH and the major and
expected Heck product could not be acquired, data were obtained from the two minor side products. The
findings reveal new opportunities for the design of novel drug candidates against FimH and offer previously
unexplored binding interactions within the active site of the protein.
Experimental Section
General. Reactions were carried out under Nitrogen using commercially available ACS grade solvents which were
stored over 4 Ǻ molecular sieves. Solutions in organic solvents were dried over anhydrous Na2SO4, filtered, and
concentrated under reduced pressure. Reagents were obtained from Sigma Aldrich Canada LTD and used without
further purification. Compounds 1 and 6 are commercially available, 2,39 and 843 were prepared according to
published data and their physical data were in agreement with the proposed structures. Melting points were
measured on a Fisher Jones apparatus and are uncorrected. Optical rotations were measured with a JASCO P-
1010 polarimeter. Reactions were monitored by thin-layer chromatography using silica gel 60 F254 coated plates (E.
1
Merck). H and 13C NMR spectra were recorded at 300 or 600 MHz and 75 or 150 MHz, respectively, with
Varian Gemini 2000 (300 MHz) and Varian Inova (600 MHz) spectrometers. All NMR spectra were measured at
25 °C in indicated deuterated solvents. Proton and carbon chemical shifts (δ) are reported in ppm relative to the
chemical shift of residual CHCl3, which was set at 7.28 ppm (1H) and 77.16 ppm (13C). Coupling constants (J) are
reported in Hertz (Hz), and the following abbreviations are used for peak multiplicities: singlet (s), doublet (d),
doublet of doublets (dd), doublet of doublet with equal coupling constants (tap), triplet (t), multiplet (m).
Assignments were made using COSY (COrrelated SpectroscopY) and HSQC (Heteronuclear Single Quantum Coherence)
experiments. High-resolution mass spectra (HRMS) were measured with a LC-MS-TOF (Liquid Chromatography
Mass Spectrometry Time of Flight) instrument (Agilent Technologies) in positive and/or negative electrospray
mode by the analytical platform of UQAM. Compounds 11-14 were only obtained in trace amounts that could not
be fully characterized except through the X-ray data of their unprotected FimH complexes (12, 14) (Figure 5). The
X-ray data were deposited as PDB accession no. 5AAL and 5AAP, respectively.
1,2,3,4,6-Penta-O-benzoyl-D-mannopyranose (4α, 4β).42 D-Mannose (3.00 g, 16.7 mmol) was dissolved in
pyridine to which was added benzoyl chloride (1:5 v/v). After stirring for 16 h at room temperature, the excess
benzoyl chloride was quenched with methanol and the reaction mixture was concentrated under vacuum. The
crude residue was dissolved in dichloromethane, washed successively with NaHCO3, brine, and dried (Na2SO4).
A crude mixture of 4α/4β (10.6 g, 14.27 mmol) was obtained. The anomeric ratio (1H NMR) of the two
anomers was (75α:25β) similar to that previously obtained from the literature.42 The residue was purified by
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flash silica gel column chromatography using (PhMe/EtOAc, 9.8:0.2) to provide 4α (40%), Rfα = 0.33 and 4β
(48%), Rfβ = 0.21. Physical data agreed with those present in the literature.42
2,3,4,6-(Tetra-O-benzoyl-α-D-mannopyranosyl)-1-propene (5α). To an ice-cold solution of 1,2,3,4,6-tetra-O-
benzoyl-α-D-mannopyranose (4) (3.46 g, 4.94 mmol) in dry acetonitrile (13 mL) and CH2Cl2 (7 mL) was added
allylTMS (1.17 mL, 1.5 equiv) followed by BF3·Et2O (1.08 mL, 1.9 equiv) and TMSOTf (0.98. mL, 1.1 equiv)
added dropwise during 20 min. The reaction mixture was heated at 50 °C under N2 for 48 h. The course of the
reaction was monitored by TLC. The solution was evaporated under reduced pressure then diluted with
dichloromethane which was washed with NaHCO3. The organic layer was separated and dried (Na2SO4),
filtered, and concentrated to provide an α/β anomeric mixture in 7:1 ratio: Rfα = 0.36, Rfβ = 0.31. Purification
and separation of α anomer was done by silica gel column chromatography (Hex/EtOAc, 4:1) to afford the title
compound 5α as a colorless powder (1.2 g, 40%): mp 112-114 °C (EtOH/Et2O); [α]20D = -62.6 (c = 0.18, CHCl3).
1H NMR (600 MHz, CDCl3): δH 7.24-8.21 (m, 20H, H-arom), 6.02 (t, 1H, J3,4 = J4,5 = 9.0, H-4), 5.91-5.84 (m, 2 H,
CH=CH2 and H-3 ), 5.71 (dd, 1H, J1,2 = J2,3 = 2.9, H-2), 5.28 (dd, 1H, Jtrans = 17.1, Jge < 1.0, CH=CHH), 5.15 (dd 1H,
Jcis = 10.2, Jgem < 1.0, CH=CHH), 4.66 (dd, 1H, J6a,6b = 12.0, J5,6a = 5.4, H-6a), 4.60 (dd, 1H, J6a,6b = 12.0, J5,6b = 2.9,
H-6b), 4.45-4.25 (m, 2H, H-1,H-5), 2.77 (ddd, 1H, J1’a,1’b = 8.5, J1’a,2’ = 7.9, J1’a,1 = 7.2), 2.65 (ddd, 1H, J1’b,1’a = 7.7,
13
:
.
J1’b,2 = 7.2, J1’b,1 = 6.4); C NMR (CDCl3) δC 166.6, 165.6, 165.5, 165.4 (4 CO), 133.4 (C-2’), 133 3, 133.3, 133.0 (C
arom-q), 129.7, 129.5, 128.9, 128.1, (C arom), 118.4 (C-3’), 74.6 (C-1), 71.2 (C-5), 70.6 (C-4), 69.9 (C-3), 67.4 (C-
2), 62.8 (C-6), 33.5 (C-1’). ESI+-HRMS: [M+H]+ calcd for C37H32O9 + H+: 621.2119, found, 621.2143.
(E)-4-[3-(2,3,4,6-Tetra-O-benzoyl-α-D-mannopyranosyl)prop-1-en-1-yl]-1,1'-biphenyl (9). To a solution of
mannoside 5α (50 mg, 0.08 mmol) in DMF were added 4-iodo-1,1’-biphenyl (45 mg, 2 equiv), 15%
palladium(II) acetate, tetrabutylammonium bromide (25 mg, 1 equiv), and sodium bicarbonate (20 mg, 3
equiv). The reaction mixture was heated at 85 °C under N2 for 24 h. The solution was concentrated under
reduced pressure and the residue was purified by flash column chromatography using silica gel column
chromatography (PhMe/EtOAc, 3:1) to afford the title compound 9 as a colorless oil (57.2 mg, 93%). [α]20D = -
1
11.05 (c = 0.7, CHCl3). H NMR (600 MHz, CDCl3) δH 8.10-7.25 (m, 29H, H-arom), 6.65 (d, 1H, J2’,3’ = 15.8,
CH=CH-biPh), 6.36-6.23 (m, 1 H, CH=CH-biPh), 5.96 (dd, 1H, J3,4 = 8.9, J4,5 = 2.0, H-4), 5.91 (dd, 1H, J2,3 = 3.0, J3,4
= 8.9, H-3), 5.20 (dd, 1H, J1,2 = 1.5, J2,3 = 3.3, H-2), 4.58 (dd, 1H, J6a,6b = 12.0, J5,6a = 6.1, H-6a), 4.50 (dd, 1H, J6a,6b
= 12.1, J5,6b = 2.8, H-6b), 4.57-4.33 (m, 2H, H-5, H-1), 3.10-2.90 (m, 1H, H1’a), 2.90-2.70 (m, 1H, H1’b); 13C NMR
:
(CDCl3) δC 171.7, 166.3, 165.6, 165.5 (4CO), 140.8, 140.0, 136.9 (C arom-q), 136.0, 133.7, 133.2, 129.9, 128.5,
126.9, (C arom, C-3’), 124.2 (C-2’), 74.6 (C-1), 71.3 (C-5), 70.8 (C-4), 69.8 (C-3), 67.4 (C-2), 63.1 (C-6), 33.0 (C-
1’). ESI+-HRMS: [M+H]+ calcd for C49H40O9 + H+: 773.2745; found, 773.2745.
(E)-4-[3-(α-D-Mannopyranosyl)prop-1-en-1-yl]-1,1'-biphenyl (10). Compound 9 (50 mg, 0.064 mmol) was
deprotected by treatment with 1 M ammonia in methanol (0.1 M) at room temperature for 36 h. Removal of
solvent under vacuum afforded the crude residue which was purified by semi-preparative HPLC (A: H2O + 0.1%
trifluoroacetic acid, B: MeCN + 0.1% trifluoroacetic acid, 5 mL/min) to afford the title compound 10 (24.9 mg,
96%). [α]20D = 30.2 (c = 1.0, MeOH). 1H NMR (600 MHz, CD3OD): δH 7.50 (d, 2H, JHH = 7.5, H-arom), 7.45 (t, 2H,
JHH = 8.2, H-arom), 7.36 (d, 2H, JHH = 8.2, H-arom), 7.31 (dd, 2H, JHH = 8.0, 15.8, H-arom), 7.20 (dd, 1H, JHH = 8.1,
15.4, H-arom), 6.45 (d, 1H, J2’,3’ = 15.6, CH=CHPh), 6.29-6.22 (m, 1H, CH=CHPh), 3.93-3.90 (m, 1H, H-1), 3.74
(dd, 1H J1,2 = J2,3 = 2.8, H-2), 3.71 (dd, 1H, J2,3 = 2.6, J3,4 = 11.7, H-3), 3.68-3.62 (m, 2H, H-4, H-6b), 3.56 (dd, 1H,
J5,6a = 9.0, J6a,6b = 8.4, H-6a), 3.48-3.41 (m, 1H, H-5), 2.67-2.51 (m, 1H, Ha’), 2.49-2.40 (m, 1H, Ha). 13C NMR (600
MHz, CD3OD): δC 140.6, 140.1, 136.9 (C arom-q), 131.6 (C-3’), 128.4, 126.8, 126.6, 126.3, 126.2, 126.0 (C arom,
C-2’), 77.2 (C-1), 74.9 (C-5), 71.2 (C-4), 70.7 (C-3), 68.0 (C-2), 61.6 (C-6), 32.5 (C-1’). ESI+-HRMS: M+NH4+ calcd
for C21H28NO5, 374.1962; found, 374.1960.
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X-Ray crystal-structure of 5α and refinement data: formula, (C37H32O9), orthorhombic, space group P212121, a
9.4849(3) Å, b 12.6698(4) Å, c 26.5906(8) Å, α 90°, β 90°, γ 90°, V 3195.44(17) Å3, Dcalcd 1.290 g/cm3, crystallize:
0.3 × 0.28 × 0.18 mm3. Index ranges-12 ≤ h ≤ 12, -16 ≤ k ≤ 16, -34 ≤ l ≤ 34. Crystallographic data for the
structure reported in this paper has been deposited at the Cambridge Crystallographic Data Centre (CCDC)
with deposition no: 1560370 for C37H32O9. Supplementary data can be obtained free of charge from CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: (+44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk, website
http://www.ccdc.cam.ac.uk).
Acknowledgements
This work was supported by grants from the Natural Science and Engineering Research Council of Canada
(NSERC) to R. Roy including a Canadian Research Chair and the Fonds du Québec – Nature et Technologies to
R.R.
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