A practical and scalable synthesis of KRN7000 using glycosyl iodide as the glycosyl donor

Article abstract of DOI:10.1177/1747519820961018

KRN7000 is particularly useful because it is a powerful and specific CD1d agonist and has prompted intense interest in the context of immunology in the past 25 years. Its limited commercial availability and high price has led to the publication of many different syntheses. However, almost all of them focused on the methodology development rather than a scalable synthesis. Herein, we have described a practical and scalable procedure for the synthesis of KRN7000 basing on the glycosyl iodide method. This procedure involves total of eight steps to obtain the highly pure product KNR7000 on gram scale from the commercially available starting materials (d-galactose and the phytosphingosine) with only three column chromatographic purifications.

Full text of DOI:10.1177/1747519820961018

961018CHL0010.1177/1747519820961018Journal of Chemical ResearchZhang et al.
research-article2020
Research Paper
Journal of Chemical Research
1–6
© The Author(s) 2020
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A practical and scalable synthesis of KRN7000
using glycosyl iodide as the glycosyl donor
https://doi.org/10.1177/1747519820961018
DOI: 10.1177/1747519820961018
journals.sagepub.com/home/chl
Yang Zhang1, Jia Guo1, Xiaoyan Xu2, Qi Gao2, Xianglai Liu1
and Ning Ding1
Abstract
KRN7000 is particularly useful because it is a powerful and specific CD1d agonist and has prompted intense interest
in the context of immunology in the past 25years. Its limited commercial availability and high price has led to the
publication of many different syntheses. However, almost all of them focused on the methodology development rather
than a scalable synthesis. Herein, we have described a practical and scalable procedure for the synthesis of KRN7000
basing on the glycosyl iodide method. This procedure involves total of eight steps to obtain the highly pure product
KNR7000 on gram scale from the commercially available starting materials (d-galactose and the phytosphingosine) with
only three column chromatographic purifications.
Keywords
α-GalCer, glycosyl iodide, glycosylation, KRN7000, phytosphingosine
Date received: 27 June 2020; accepted: 3 September 2020
OH
HO
HO
OTMS
O
2 steps
OH
TMSO
TMSO
O
OTMS
O
OH
TMSO
TMSO
HO
HO
O
O
OH
O
TMS
O
C25H51
OH
I
O
HN
D-galactose
2 steps
HN
OTBS
C14H29
OTBS
> 2 gram / single step
1 step
O
OH
O
TMS
O
C14H29
OH
> 2 gram
O
O
3 steps
KRN7000
8 steps
recover
NH2 OH
HN
OTBS
HO
HO
C14H29
OH
OTBS
> 20 gram
3 colomn chromatagraphy
Gram scale
phytosphingosine
KRN7000 was prepared through eight steps on gram scale from the commercially available starting materials with only
three column chromatography purifications.
applications.8 Therefore, a number of subsequent studies
have focused on the ability to control the cascade by attempt-
Introduction
KRN7000, also referred to as α-galactosyl ceramide (α-
ing to bias the Th1/Th2 cytokine release profile by employ-
GalCer), is an analogue of natural α-GalGSLs isolated from
the marine sponge Agelasmauritianus,1 and is the most
extensively studied ligand for invariant natural killer T
(iNKT) cells,2,3 demonstrating immune stimulatory activity
and antitumor properties.4,5 KRN7000 binds to the protein
CD1d, contributes to the glycolipid-protein complex and is
recognized by T cell receptors (TCRs) positioned on the
exterior of iNKT cells resulting in activation of the immune
response by releasing both Th1 (IFN-γ) and Th2 (IL-4)
cytokines.6,7 However, the opposing activities of the simul-
taneously secreted Th1 and Th2 cytokines are considered a
major limitation of KRN7000 for its potential therapeutic
ing KRN7000 as the template.4,9,10 So far, many clinical
studies on the development of a novel CD1d-binding NKT
cell ligand as an additive vaccine adjuvant based on
1Department of Medicinal Chemistry, School of Pharmacy, Fudan
University, Shanghai, P.R. China
2China State Institute of Pharmaceutical Industry, Shanghai, P.R. China
Corresponding author:
Ning Ding, Department of Medicinal Chemistry, School of Pharmacy,
Fudan University, 826 Zhangheng Road, Shanghai 201203, P.R. China.
Email: dingning@fudan.edu.cn
Creative Commons Non Commercial CC BY-NC: This article is distributed under the terms of the Creative Commons
Attribution-NonCommercial 4.0 License (https://creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use,
reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and
Open Access pages (https://us.sagepub.com/en-us/nam/open-access-at-sage).

2
Journal of Chemical Research 00(0)
KRN7000 analogues are ongoing (Th1 cytokine bias).11
Besides, KRN7000 analogues bearing functional groups are
potentially versatile in conjugation strategies through facile
reactions with a wide range of substrates to form highly
defined synthetic vaccines, which has prompted intense
interest in the context of “self-adjuvanting” vaccines.12–15
On the other hand, the efficient synthesis of KRN7000 and
its analogues is not an easy task. Its limited commercial avail-
ability and high price has led to the publication of many dif-
ferent syntheses.4 Although the formation of 1,2-trans
glycosides can be easily achieved by taking advantage of
neighboring group assistance, such as O-acetyl or O-benzoyl
at C-2, the stereospecific construction of the 1,2-cis-galacto-
pyranosyl linkage present in KRN7000 remains one of the
greatest challenges.16–18 1,2-cis-Gal-type linkages can be
formed under thermodynamic conditions (anomeric effect),
in appropriate solvents (solvent effect), and using nonpartici-
pating protecting groups at the C2 hydroxy, typically benzyl
groups.19–21 Glycosyl trichloroacetimidates are the most pop-
ular glycosyl donors for glycosylation of azido-
sphingosine,22,23although SPh, OAc, and other leaving groups
have also been employed.16 However, all of the mentioned
strategies require extensive protecting group manipulations to
secure the stereo- and regio-selectivity. For example, in our
previous work,22,24,25 the thiogalactoside donor with a ben-
zylidene/naphthylidene group at O-4/O-6 and nonparticipat-
ing benzyl/(2-naphthyl)methyl groups at O-2/O-326 were
successfully glycosylated with an azido-phytosphingosine
acceptor to construct the glycolipid scaffold with exclusive
1,2-cis selectivity, and was then transformed into the final α-
GalGSLs by azide reduction, amide formation, and deprotec-
tion. The construction of the required donor building block
needed at least five steps from d-galactose usually. Besides,
the phytosphingosine acceptor often needs an azido group as
the amino precursor, since a 2-amine group (even partially
OH
OH
OH
HO
OH
HO
O
O
O
C25H51
OH
HN
NH2 OH
C14H29
OH
OH
O
O
C14H29
OH
OH
1
KRN7000
OTMS
O
O
TMSO
TMSO
O
OTMS
TMSO
TMSO
O
OTBS
O
O
HN
+
HN
OTBS
C14H29
OTBS
HO
O
TMS
C14H29
OTBS
O
O
TMS
I
4
3
2
OH
HO
HO
NH2 OH
O
HO
C14H29
OH
OH
OH
phytosphingosine
D-galactose
Scheme 1. The retrosynthesis of KRN7000.
iodide strategy expressed in the synthesis of the α-GalCers,
we decided to investigate this technique. There are a number
of cases that have been reported so far; however, they all
focused on methodology development, and none of them
were aimed to work a scalable synthesis. Herein, we describe
a practical and scalable procedure for the synthesis of
KRN7000 based on the glycosyl iodide method initially
developed by the Gervay-Hague group. In our optimized
procedure, there are a total of eight steps to obtain the highly
pure product KRN7000 in up to gram scale from the com-
mercially available starting materials d-galactose and the
phytosphingosine, with only three column chromatographic
purifications.
Results and discussion
protected) could form a hydrogen bond with the 1-OH to The general retrosynthesis of KRN7000 is shown in
reduce the glycosylation yield.16 The transformation of an Scheme 1. The glycolipid scaffold 2 with a 1,2-cis-glyco-
amino group into an azido group is extremely dangerous, sidic bond could be formed by glycosylation of the glyco-
especially in the large-scale operations.27
syl iodide 3 with the partially protected phytosphingosine
The group of Gervay-Hague developed a strategy in 4. The glycosyl iodide 3 was easily prepared from commer-
which per-O-silylated galactosyl iodides28 undergo α- cially available d-galactose by persilylation followed by
exclusive glycosidation with fully functionalized glycolip- the introduction of the anomeric iodide. As for the acceptor
ids producing biologically relevant glycolipids.29,30 This is 4, the Boc (t-Butyloxy carbonyl)-protected amino group
very attractive alternative strategy for the synthesis of α- was selected to avoid the use of an azido group. Besides,
GalCers. First, the use of per-O-silylated galactosyl iodide the two secondary hydroxy groups were also protected by
avoided the tedious protecting group installations on the silyl groups to facilitate the later deprotection procedure.
donor before the glycosylation. Besides, the same group29
At the beginning, we followed the reported procedure
also reported that direct incorporation of ceramide accep- for the synthesis of acceptor 4, as shown in Scheme 2.31 The
tors to connect with the per-O-silylated galactosyl iodides 2-NH2 of the phytosphingosine was protected with a Boc
were quite possible, which avoided the use of azido groups group first and then the triol was silylated. Introduction of
in the acceptor. Based on this method, they successfully the Boc group was smooth to provide 5 using a slight excess
achieved the formal synthesis of KRN7000.30 Others have of Boc2O in the presence of Et3N (triethylamine), and the
used optimized methods to synthesize several other α- corresponding product could be isolated from the reaction
GalCers,31 C-linked sugars,32 oligosaccharides, and glyco- mixture by crystallization. Unfortunately, the subsequent
conjugates which present potential applications as cancer protection of three hydroxys with TBS (t-butyldimethysi-
vaccines or as adjuvant candidates.33
lyl) groups proved difficult. On treatment with a large
Due to the long-term interest in their relevant biological excess of TBSOTf (up to 5equiv.) in the presence of
properties, our group has focused on the syntheses of α- 2,6-lutidine (14.8equiv.), the target product 7 was provided
GalGSLs for many years22,24,25,34 and have tried to develop a always along with the partially protected 6. When the reac-
practical and scalable synthetic procedure for KRN7000 and tion temperature was increased to 40°C and stirred for 2h,
its analogues. In view of the advantages of the galactosyl the Boc group was cleaved to provide a mixture of 8 and 9.

Zhang et al.
3
BoC2O (1.04 eqiv),
TEA (1.2 eqiv)
THF
TBSOTf (5.0 eqiv),
2,6-lutidine (14.8 eqiv)
CH2Cl2
NHBoc
OH
OTMS
O
HMDS (4.3)/
TMSCl (3.5)
pyridine
OTMS
O
TMSO
TMSO
TMSO
TMSO
NH2 OH
HO
TMSI (1.0)
dry CH2Cl2
HO
C14H29
D-galactose
C14H29
r.t. 2h 98%
r.t. 48h
75 oC, 1 h
quant. (crude)
0 oC, 30 min
O
TMS
O
TMS
OH
OH
I
OTMS
5
3 (1.0)
11
NHBoc
OH
NHBoc
OTBS
Bu4NI (2.0)
DIPEA (1.5)
molecular sieves
r.t., overnight
26%
NH2 OH
C14H29
TBSO
TBSO
HO
C14H29
OTBS
C14H29
OTBS
4 (0.33)
OTBS
8
6
40 oC, 2h
recover 72%
+
+
NHBoc
OTBS
OTMS
O
TMSO
TMSO
NH2 OTBS
C14H29
OTBS
O
TBSO
O
TBSO
C14H29
OTBS
HN
OTBS
C14H29
OTBS
silica gel chromatograpgy needed
O
TMS
9
O
7
2
Scheme 2. The initial procedure for the synthesis of acceptor 3.
Scheme 4. Preparation of the glycosyl iodide and the
glycosylation with 3.
TBSOTf (5.0)/
2,6-lutidine (14.8)
CH2Cl2
NH2 OTBS
C14H29
NH2 OH
C14H29
TBSO
HO
was subjected to the glycosylation with acceptor 4 without
further purification. A solution of crude glycosyl iodide 3 in
dry CH2Cl2 was added to a dichloromethane solution of
acceptor 4 in excess, which was premixed with n-Bu4NI
(tetrabutylammonium iodide), a promoter that accelerates
the reaction and determines the α-stereoselectivity through
in situ anomerization.28 After the indicated time, the solvent
was evaporated and the remaining residue was subjected to
column chromatography to give product 2. Although the
literatures29,30 claimed high yielding of the α-glycolipids
using this silylated galactosyl iodide strategy in many
cases, however, in our hands, the yield of this glycosylation
reaction was quite low with complete recovery of the
acceptor 4. Also, the tetramethylsilane (TMS) group is
highly sensitive to acid condition, there is a possibility that
r.t., 2 h, 98% (crude)
OTBS
OH
10
Boc2O (1.04)
Et3N (1.2), THF
98% (crude)
r.t.
2 h
NHBoc
NHBoc
OTBS
HF-Py (6.9 eqiv)
THF: Py (65:35 v:v)
THF
0 oC to r.t.,1.5 h
81% over 3 steps
OTBS
C14H29
OTBS
HO
TBSO
C14H29
OTBS
7
4
silica gel chromatograpgy needed
Scheme 3. The optimized procedure for the synthesis of
acceptor 3.
Alternatively, a modified procedure by adjusting the TMS groups were cleaved during column chromatographic
protection sequence was carried out. The commercially purifications, which may also account for the low yield of
available phytosphingosine first underwent silylation to compound 2. Extensive reaction condition screenings were
provide silyl ether 10 by treatment with 5equiv. of TBSOTf then performed. The ratio of the galactosyl iodide over the
in the presence of a base. The free amine of crude 10 was acceptor was enhanced from 1:1 to 10:1 in a stepwise man-
then protected with a Boc group to provide 7. Compound 7 ner, and the best ratio was found to be 3:1. Besides, the
then underwent selective monodeprotection of the primary reaction temperature, reaction time, and the equivalents of
silyl ether with HF-pyridine to afford the glycosyl acceptor the reagents were all screened. As shown in Scheme 4,
4. It should be noted that in this optimized procedure, all under the optimized conditions, the best yield of this glyco-
three steps were performed efficiently. Therefore, the crude sylation reaction was still only 26% after column chroma-
products of the first two steps were pure enough to be sub- tography. But fortunately, most of the unreacted acceptor 4
jected to the next step after routine work-up without further could be recovered (72%). It should be noted that in this
purification. Thus, only one silica gel chromatography procedure the galactosyl iodide could be obtained from
purification was needed for the final acceptor 4 before it inexpensive d-galactose conveniently by a two-step
was subjected to the subsequent glycosylation with a glyco- sequence without purification; thus, the relatively more
syl iodide. Acceptor 4 was prepared on 20-gram-scale by complex acceptor 4 should be the time- and cost-determin-
employing this procedure (Scheme 3).
ing substrate. The recovered acceptor 4 could be glyco-
Crude per-O-trimethylsilyl d-galactose 11 was prepared sylated again with galactosyl iodide 3 under the same
quantitatively by treating d-galactose with chlorotrimethyl- conditions. The recovery of the acceptor 4 made this proce-
silane (TMSCl) and hexamethyldisilazane (HMDS) in the dure practical and scalable, despite the glycosylation yield
presence of pyridine followed by removal of the excess rea- not being satisfactory. We proved that the glycosylation
gents and solvent. By treating with TMSI in dichlorometh- step could be carried out on over a 2-gram-scale basing on
ane, crude 11 was transformed into the corresponding the acceptor 4. By repeating the glycosylation, up to 10g of
galactosyl iodide 3 smoothly (Scheme 4). Upon comple- 2 were prepared quickly.
tion, the remaining TMSI and the solvent were removed
The glycolipid 2 was subsequently subjected to HCl/
under reduced pressure and the resulting glycosyl iodide MeOH for 1h to remove all of the protecting groups,

4
Journal of Chemical Research 00(0)
Synthesis of (2S,3S,4R)-2-[(N-tert-
C25H51C(O)Cl
THF /NaOAc (aq)
(8 M 1:1)
OH
OH
OH
HO
O
OH
HO
4 M HCl/
MeOH
butoxycarbonyl)amino]-3,4-ditert-
O
C25H51
OH
O
Cl
NH3
HN
2
OH
butyldimethylsilyloxyoctadecan-1-ol (4)
OH
53% over 2 steps
OH
r.t.,1 h
O
O
R
R
OH
A solution of phytosphingosine (18.0g, 43.2mmol) in
CH2Cl2 (600mL) at 0°C was treated sequentially with
TBSOTf (49.5mL, 217.2mmol) and 2,6-lutidine (75mL).
There mixture was stirred at 0°C at first, and then warmed
to 25°C and stirred at this temperature for 4h, after which
time, CH3OH (150mL) was added and stirring was contin-
ued for 10min. The solvent was then removed under
reduced pressure, and the residue taken up in Et2O (450mL)
and washed sequentially with H2O (450mL), NaHCO3
solution (450mL), and brine (450mL). The organic phase
was dried over Na2SO4, filtered, and evaporated to give
crude compound 10 as a colorless oil (98% crude), which
was used directly in the next step without any further
purification.
Et3N (7.20mL, 51.9mmol) and Boc2O (9.9g, 45.0mmol)
were added sequentially to crude compound 10 (28.5g,
43.2mmol) dissolved in THF (390mL). After 2h, the reac-
tion mixture was concentrated under reduced pressure, dis-
solved in EtOAc (450mL), and washed with H2O (3×
450mL) and brine (450mL). The organic phase was dried
over Na2SO4, filtered, and evaporated to give crude com-
pound 7, which was used directly in the next step without
any further purification (98% crude).
OH
1
R = -C14H29
KRN7000
silica gel chromatograpgy needed
Scheme 5. Synthesis of KRN7000.
resulting in amine 1. Treating a biphasic mixture of amine
1 in THF/8-M aqueous NaOAc with hexacosanoyl chlo-
ride provided the crude product KRN7000. Purification of
the crude residue by silica gel flash column chromatogra-
phy (gradient: CHCl3 to 15% MeOH in CHCl3) afforded
the final product KRN7000 as a white solid (53% over
two steps). (Scheme 5) The purity of the prepared
KRN7000 analyzed by HPLC was about 94% (see the
Supporting Information), which has the same quality as
those sold by commercial supplies (e.g. the indicated
purities of KRN7000 from several main commercial
resources are >99% based on TLC (the Funakoshi);
>95% based on TLC (Sigma-Aldrich); 95% based on LC
(J&K).). Both of the two steps proved effective on over
2-gram-scale.
Conclusion
A solution of 7 (33.0g, 51.9mmol) in THF (600mL)
under a N2 atmosphere at 0°C was treated with HF·pyridine
(7.80mL of a 70% solution, 298.5mmol) in THF–pyridine
(41.7mL, 65:35). The reaction mixture was stirred for
30min at 0°C and then allowed to warm to rt. After 1h,
the mixture was quenched by the addition of NaHCO3
solution (28.5mL) and stirred for 10min. The reaction
mixture was extracted with EtOAc (2× 450mL), and the
combined organic phase was washed with brine (450mL)
and then filtered. Removal of the volatiles under reduced
pressure and purification of the residue by flash column
chromatography afforded primary alcohol 4 as a light yel-
lowish oil (21.6g, 81% over three steps). 1H NMR
(400MHz, CDCl3): δ 5.22 (d, J=8.3Hz, 1H), 4.09 (d,
J=7.4Hz, 1H), 3.85 (s, 1H), 3.73 (s, 2H), 3.60 (s, 1H),
3.01 (s, 1H), 2.02 (s, 1H), 1.67 (s, 1H), 1.41 (s, 10H), 1.23
(s, 26H), 0.88 (d, J=7.3Hz, 21H), 0.08 (s, 9H). 13C NMR:
(151MHz, CDCl3): δ 79.19, 77.45, 76.06, 63.19, 60.15,
52.26, 34.07, 31.91, 29.66, 28.42, 25.97, 22.67, 20.92,
In summary, a practical and scalable procedure for the
synthesis of KRN7000 based on the glycosyl iodide
method was developed. This procedure involved a total
of eight steps to obtain the highly pure product KRN7000
on gram scale from the commercially available starting
materials d-galactose and the phytosphingosine. Two key
advantages of this procedure are that only three column
chromatographic purifications were needed and the use
of azido groups in the glycosyl acceptor was avoided.
Experimental
Unless otherwise noted, all materials and dry solvents
were used as received from Adamas-beta® without fur-
ther purification. 1H and 13C NMR spectra were recorded
on Varian Mercury 400-MHz or Bruker 600-MHz spec-
trometers. Chemical shifts are reported in parts per mil-
lion (ppm) relative to TMS (δ 0). NMR data are
presented as follows: chemical shift, multiplicity
(s = singlet, d = doublet, t = triplet, dd = doublet of dou-
blet, m = multiplet and/or multiple resonances), cou-
pling constant in hertz (Hz), integration. All NMR
C35H75Si2 NNaO5+
14.09, −3.78. ESI-MS: m/z calcd. for
[M+Na]+ 668.5, found 668.5. The physical data matched
those previously reported.31
1
signals were assigned on the basis of H NMR, 13C
Synthesis of (2S,3S,4R)-2-[(N-tert-
butoxycarbonyl)amino]-3,4-di-tert-
butyldimethylsilyloxy-1-O-(2,3,4,6-tetrakis-
O-trimethylsilyl-α-d-galactopyranosyl)
octadecane (2)
NMR, COSY, HSQC, and HMBC experiments. Mass
spectra were recorded on a Q-Tof Ultima Global mass
spectrometer or a Shimadzu LCMS-IT-TOF mass spec-
trometer. TLC-analysis was performed on silica gel 60
F254 (Huang Hai Inc.) with detection by UV-absorption
(254 nm) when applicable, and by spraying with a solu-
tion of (NH4)6Mo7O24·H2O (25 g L−1) in 5% sulfuric acid
in ethanol followed by charring. All reactions were car-
ried out under an argon atmosphere.
TMSI (3.25 mL, 23.89 mmol) was added to a solution of
per-silylated galactose 11 (13.0 g, 23.89 mmol) in dry
CH2Cl2 (95 mL) at 0 °C. The reaction mixture was stirred
under an N2 atmosphere for 30 min. The solvent was

Zhang et al.
5
Program, China” (2018ZX09711002-006-008) and “Shanghai
Science and Technology Innovation Fund” (17431902400).
removed under reduced pressure and the resulting glyco-
syl iodide intermediate 3 was dissolved in dry CH2Cl2
(50 mL) and kept under an N2 atmosphere. In a separate
flask, a mixture of activated 4-Å molecular sieves
(16.0 g), n-Bu4NI (17.55 g, 47.78 mmol), i-Pr2NEt
(15.6 mL, 35.95 mmol), and alcohol 4 (5.14 g, 8.45 mmol)
in dry CH2Cl2 (95 mL) was prepared and stirred under an
N2 atmosphere at rt. for 15 min. The solution of glycosyl
iodide 3 in CH2Cl2 was then added dropwise over 5 min
to this mixture, and the resulting mixture was stirred
overnight. After removal of the solvent under reduced
pressure, Et2O (130 mL) and H2O (130 mL) were added
and the phases were separated. The organic phase was
dried (Na2SO4) and then concentrated under reduced
pressure. The resulting yellow solid was purified by
flash column chromatography (3% EtOAc in hexane
with 0.3% Et3N) to afford glycoside 2 as a colorless oil
(2.40 g, 26%) and recovered 4 as a light yellowish oil
ORCID iD
Ning Ding
https://orcid.org/0000-0002-6797-8797
Supplemental material
Supplemental material for this article is available online.
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(3.93 g, 72%). H NMR (400 MHz, CDCl3): δ 5.21 (d,
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Synthesis of KRN7000
HCl/MeOH (4M, 10mL) was added to glycoside 2 (2.8g,
2.55mmol) at rt. After 40min, the reaction mixture was
concentrated under reduced pressure to afford compound 1
as colorless oil (1.2-g crude), which was used directly in the
next step without further purification.
A solution of hexacosanoic acid (2.4g, 6.0mmol) in
(COCl)2 (40mL) was stirred at 70°C for 2h, after which
time, the solution was cooled to rt, and the excess (COCl)2
was removed under reduced pressure. The resulting crude
acyl chloride was dissolved in THF (60mL) and added,
with vigorous stirring, to a solution of amine 1 (1.50g,
2.50mmol) in THF/NaOAc (aq) (8M) (1:1, 120mL).
Vigorous stirring was maintained for 2h. The mixture was
left to stand, and the phases were separated. The aqueous
phase was extracted with THF (2× 120mL), and the com-
bined organic phases were evaporated under reduced
pressure. Purification of the residue by flash column chro-
matography (gradient: CHCl3 to 15% MeOH in CHCl3)
afforded the final product KRN7000 as a white powder
(2.26g, 53% over two steps). The physical data matched
those previously reported.35
Declaration of conflicting interests
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The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The author(s) disclosed receipt of the following financial support
for the research, authorship, and/or publication of this article: This
work was supported by “the National Science and Technology
Major Project Key New Drug Creation and Manufacturing
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