Diversity-Oriented Synthesis of Steviol Glycosides

Article abstract of DOI:10.1021/acs.joc.8b01274

With cheap and easily available mixtures of steviol glycosides as starting materials, a practical method for steviol acquisition has been developed, on the basis of which a facile, diversity-oriented, and economic protocol for the synthesis of structurally defined steviol glycosides was established. The novel approach is featured by the highly efficient glycosylation of sterically hindered and acid-sensitive steviol via orchestrated application of Yu glycosylation, Schmidt glycosylation, and PTC glycosylation. Hence, these high-intensity sweeteners and potential lead compounds for drug development are now readily accessible.

Full text of DOI:10.1021/acs.joc.8b01274

Subscriber access provided by University of South Dakota
Article
Diversity-Oriented Synthesis of Steviol Glycosides
Zhi Qiao, Hui Liu, Jing-Jing Sui, Jin-Xi Liao, Yuan-Hong Tu, Richard R. Schmidt, and Jian-Song Sun
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b01274 • Publication Date (Web): 05 Sep 2018
Downloaded from http://pubs.acs.org on September 6, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
DiversityꢀOriented Synthesis of Steviol Glycosides
a
a
a
a
a
Zhi Qiao, Hui Liu, JingꢀJing Sui, JinꢀXi Liao, YuanꢀHong Tu, Richard R.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
a,b,
a,
Schmidt, * and JianꢀSong Sun *
a
The National Research Centre for Carbohydrate Synthesis, Jiangxi Normal
University 99 Ziyang Avenue, Nanchang 330022 (China)
jssun@jxnu.edu.cn
b
Department of Chemistry, University of Konstanz, D-78457, Konstanz, Germany
richard.schmidt@uni-konstanz.de
Table of content:
Abstract: With cheap and easily available mixtures of steviol glycosides as starting
material, a practical method for steviol acquisition has been developed, based on
which a facile, diversityꢀoriented and economic protocol for the synthesis of
structurally defined steviol glycosides was established. The novel approach is featured
by the highly efficient glycosylation of sterically hindered and acidꢀsensitive steviol
via orchestrated application of Yu glycosylation, Schmidt glycosylation and PTC
glycosylation. Hence, the highꢀintensity sweeteners and potential lead compounds for
drug development are now readily accessible.
Introduction
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
FDA accepted in 2010 the statement that steviol glycosides (rebaudienosides,
1
Figure 1) are "Generally Recognized As Safe" (GRAS). Thus, the rapid development
2
of stevioside industry and health benefit studies were promoted, as steviosides are
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
regarded as zeroꢀcaloric, powerful sweeteners of natural origin. In addition, they
3
possess also a long application history. The unpleasant sensory property of the widely
applied stevioside sweetener as well as the unclear function mechanisms of bioactive
steviosides call on an efficient approach to obtain pure and ample amounts of
individual steviosides. Furthermore, for stevioside feedstock manufacturers, the
establishment of accurate quality control system also requires an easy access to
various pure steviosides as reference compounds.
Figure 1. The chemical structures of rebaudioside A, D, and M.
Existing methods for pure stevioside acquisition, including phytochemical
4
5
isolation and enzymatic synthesis, suffer from tedious processes and low efficiency,
6
due to the heterogeneity either of naturally occurring steviosides or of the products
obtained via enzymatic synthesis. Chemical synthesis holds the promise to solve the
sample access problem. However, the chemical structure of steviosides, containing the
acidꢀsensitive entꢀkaurene skeleton as aglycon and branched sugar chains at the
ACS Paragon Plus Environment

Page 3 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
tertiary Cꢀ13 hydroxy group and at the Cꢀ19 carboxylic group, poses a considerable
synthetic challenge. As shown in Figure 2, under acidic conditions steviol derivatives
are prone to undergo WagnerꢀMeerwein rearrangement or double bond migration
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
7
reaction to afford isosteviol and double bondꢀshifted byproducts. As a result, despite
of a long investigation history, the chemical synthesis of steviosides has only been
reported sporadically with structurally simple steviosides as target molecules; in
addition, the reaction protocol was based on the use of stoichiometric amounts of
8
toxic heavy metals and low to moderate overall yields were recorded. The urgent
need of pure steviosides coupled with our continuous efforts to synthesize naturally
9
occurring glycosides promoted us to develop an efficient, diversityꢀoriented as well
as economic synthetic strategy to produce steviosides, culminating in the first total
synthesis of rebaudiosides A, D and M. Among these target compounds rebꢀD (2) has
been regarded as ‘the gold of the steviosides’, due to the improved flavor and low
6
natural content (0.3ꢀ0.8%); moreover, rebꢀM (3) has been proven to possess even
better taste than rebꢀD, although an extremely low natural content (0.06%) was
10
detected.
Figure 2. Acidꢀelicited rearrangements of steviol aglycon.
Results and Discussion
For high efficiency of the designed synthesis, a modular strategy is required that
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
takes diversity and flexibility into account. To this end, the target molecules 1ꢀ3 were
projected to be assembled by building blocks 4ꢀ7 with 4 as building block for all
target molecules (Figure 3). Due to the acidity of the Cꢀ19 carboxylic group, the
installation of the sugar chain was envisioned to be achievable with glycosyl bromides
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
5
, 6 and 7 as glycosyl donors in the presence of base under phaseꢀtransfer conditions
11
(
PTC). The PTC glycosylation protocol could on one hand ensure the structural
integrity of the acid sensitive steviol aglycone; on the other hand, the diversity as well
as the convergency of the whole synthetic strategy could also be expected simply by
employing different glycosyl bromide donors. In turn, to generate the common
1
2
building block 4, the mild Yu glycosylation protocol and, more ideally from the
13
synthetic cost perspective, the Schmidt glycosylation method could be conceived.
Figure 3. Retrosynthetic analysis of rebaudioside A, D, and M.
First of all, a practical process for steviol acqusition had to be installed. To this goal,
14
the acidic hydrolysis of S. rebaudiana leaves was investigated (Scheme 1). To
suppress the acidꢀcatalyzed steviol rearrangement to a practical extent, a panel of
ACS Paragon Plus Environment

Page 5 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
acids were screened at different concentrations and temperatures, finally leading to
optimal conditions of 0.04 M HCl at 95 °C for 28 h. Under these conditions, the
desired steviol was obtained accompanied by isosteviol and the doubleꢀbond migrated
product (from C16,17 to C15,16) in a 1:1:1 ratio. The crude products containing
steviol precipitated from the reaction mixture, and after filtration and recrystallization
from methanol, the mixture was directly silylated (or naphthylmethylated) at the
carboxylic group and then epoxidized to generate 8a, 8b and 8a’, 8b’, respectively.
These compounds can be easily purified by silica gel chromatography (> 5g of 8a or
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
8a’/100 g stevioside mixture). The epoxidation step was introduced to facilitate the
elimination of the doubleꢀbondꢀmigrated sideꢀproducts 8b and 8b’ from 8a and 8a’,
15,16
respectively.
Restoration of the C16,17 doubleꢀbond was achieved quantitatively
17
4
by reduction with Zn/CuSO /NaI in the presence of acetic acid to produce 9 or 9’.
Interestingly, the epoxide reduction occurred selectively at the disubstituted epoxides
in 8a or 8a’) while keeping the trisubstituted epoxides (in 8b and 8b’) untouched.
(
Based on this observation, access to 9 or 9’ was finally realized via four sequential
steps with only one silicaꢀgel purification. Also appealing is that this process can be
easily scaled up and ten grams of 9 or 9’ can be conveniently obtained in one batch.
Though resistant to the epoxide reduction conditions, 8b could undergo with I
2 3
/PPh
WagnerꢀMeerwein rearrangement to afford 10; the structure of 10 was confirmed by
1
6,18
Xꢀray analysis.
Because of the problems encountered in Nap cleavage in 9’ in
model reactions, the silyl ester 9 was chosen for the following studies.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Scheme 1. Acquisition of acceptor 9 via acid hydrolysis of stevioside mixture as well
as related derivatizations.
With ample amounts of 9 in hand, the stage was now set for the construction of the
common building block 4 (Scheme 2), which was deemed as a challenging task owing
to both the acid sensitivity of the aglycone and the less accessible property of the
tertiary Cꢀ13 hydroxy group. According to the experience gained in our precedent
synthetic investigation of ginsenosides, for the generation of the branched sugar chain
the glycosylation of 2ꢀOH before 3ꢀOH of the core glucosyl residue was checked first,
as for the 2ꢀhydroxy group next to a sterically demanding aglycone at the anomeric
19
position an extremely low reactivity was expected. Taking the acid sensitivity of
acceptor 9 into account, the orthogonally protected glycosyl donor 13 with a
levulinoyl (Lev) group at 2ꢀO, an allyl (All) group at 3ꢀO and benzylidene protection
at 4,6ꢀO was investigated first, as 13 can be activated under mild conditions with a
3 2
gold catalyst (Ph PAuNTf , 0.2 equiv). The synthesis of 13 commenced with
20
glucoside 11 , which was subjected to levulinoylation under standard conditions to
ACS Paragon Plus Environment

Page 7 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
afford 12 (94%). Anomeric 4ꢀmethoxyphenyl (MP) hydrolysis was followed by
dehydrative oꢀalkynylbenzoylation to provide donor 13 (82%, 2 steps). Although the
ensuing glycosylation between 13 and 9 entailed the bulky tertiary Cꢀ13 hydroxy
group of steviol, the reaction proceeded efficiently under the catalysis of the Au(I)
complex to furnish 14 in excellent yield (95%). Hydrazinium acetate mediated
cleavage of the Lev group led to glycoside acceptor 15, which was ready for the
introduction of a glucosyl residue at the 2ꢀhydroxy group. Again, Au(I)ꢀcatalyzed
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
21
glycosylation of 15 with known donor 16 furnished disaccharide 17 very efficiently
(92%). The liberation of the 3ꢀhydroxy group of the core glucosyl residue in 17 was
achieved by the removal of the All group under standard conditions affording acceptor
18 (78%). However, the glycosylation of 18 with donor 16 failed and even the more
22
powerful Ph
3
PAuOTf catalyst did not lead to any trace amount of the desired
trisaccharide 19. After all attempts, either by increasing the amounts of donor and
promoter or by applying a more reactive 6ꢀOꢀsilylated glycosyl donor, that were all
met with failure, this route was abandoned.
23
In fact, similar problems have been previously encountered by our and other groups.
Therefore, the sequence of branch sugar introductions was reversed (Scheme 2). Thus,
removal of the 3ꢀOꢀAll group prior to the 2ꢀOꢀLev group in 14 was conducted to
provide acceptor 20, which is ready for the glycosylation at the 3ꢀhydroxy group.
Glycosylation with donor 16 under standard conditions furnished disaccharide 21 in
excellent yield (92%). Finally, the decisive glycosylation of disaccharide acceptor 22,
obtained from 21 by selective cleavage of the 2ꢀOꢀLev group, with donor 16 was
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
carried out; to our satisfaction, the desired branched trisaccharide 19 was obtained in a
respectable 90% yield. Although in 19 two identical sugar moieties are contained, the
established stepwise introduction strategy is apparently also applicable to the
generation of analogues with different entities that constitute the branched sugars;
thus the desired flexibility of the synthetic approach is exhibited.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Scheme 2. The assembly of trisaccharide glycoside 19 via different branch sugar
introduction sequence with glycosyl oꢀalknylbenzote as donors.
As the branched sugar moieties at the Cꢀ13 hydroxy group of steviosides contains
generally identical residues, the strategy to install the branched sugar residues at the
2
3
ꢀ and 3ꢀhydroxy group simultaneously in a oneꢀpot reaction was explored (Scheme
). As a prerequisite, the glycosylation should follow the sequence of 3ꢀhydroxy
group first and then 2ꢀhydroxy group of the diol acceptor 27; otherwise, the reaction
would not continue after the 2ꢀOꢀglycosylation and only the 1,2ꢀlinked disaccharide
24
would be obtained. For this study known glucose derivative 23 was acylated to
ACS Paragon Plus Environment

Page 9 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
deliver 24, which was then subjected to thioglycoside hydrolysis and
oꢀalkynylbenzoylation to generate the Yu donor 25 (90%, 2 steps). The ensuing
coupling of 9 with donor 25 went smoothly, affording glycoside 26 in an excellent 91%
yield. The following cleavage of the two Lev groups provided the desired acceptor 27
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(84%). To our delight, the pivotal Au(I)ꢀcatalyzed glycosylation of 27 with donor 16
(3.0 equiv) followed the desired glycosylation sequence to generate trisaccharide 19
(88%) and no premature 1,2ꢀlinked disaccharide was detected. Finally, desilylation of
the Cꢀ19 silyl ester of 19 was performed with TBAF/acetic acid to give the common
building block 4 in very good overall yield.
Scheme 3. Synthesis of the common building block 4 via simultaneous branch sugars
introduction with Yu donors.
Allured by the dramatic drop in synthetic cost with glycosyl trichloroacetimidate as
donors, the fabrication of the key building block 4 with Schmidt donor was tried
under the risk of aglycone rearrangement under acidic conditions. To seek for the
25
optimal glycosylation conditions for Schmidt donors, the coupling between 25’ and
acceptor 9 was examined systematically (Table 1). Under the effect of TMSOTf at
room temperature, the glycosylation delivered monosaccharide glycoside 28 with the
double bond of the aglycone migrated from C16,17 to C15,16 (91%, entry 1). A
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
o
similar result was recorded when the reaction was conducted at 0 C (94%, entry 2).
o
In sharp contrast, once the reaction temperature was decreased to ꢀ20 C, the
undesired double bond shift reaction was suppressed to such an extent that 26 and 28
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
were isolated with a ratio of 6 : 1 (93%, entry 3). Further lowering the reaction
o
temperature to ꢀ40 C, the side reaction was prohibited completely, and the desired
glycosylation product 26 was isolated in an excellent 96% yield (entry 4).
Mechanistically, the double bond migration of the aglycone takes place prior to
glycosylation reaction, as the control reaction of 9 with TMSOTf (0.2 eq) in the
absence of donor 25’ revealed that the migration reaction proceeded so rapidly that it
o
could reach completion in less than 5 minutes at 0 C. It deserves further comments
that under the effect of TMSOTf, the entꢀkaurene aglycon 9 only undergoes double
bond migration reaction and no WagnerꢀMeerwein rearrangement byproduct was
detected.
Table 1. Optimization of glycosylation reaction between Schmidt donor 25’ and 9.
Ph
Ph
Ph
O
O
O
O
O
O
O
OTCAI
OLev
LevO
O
O
2
5'
OLev
O
OLev
O
TMSOTf (0.2 eq)
+
17
+
OH
4A MS, CH2Cl2
16
1
6
Temperature
1
5
O
O
O
OTBDPS
OTBDPS
OTBDPS
26
28
9
Entry Temperature
Resulta
Entry Temperature
Resulta
-20 o
-40 o
1
2
rt
0 o
only 28 (91%)
only 28 (94%)
3
4
C
C
26 (80%), 28 (13%)
only 26 (96%)
C
a
Isolated yield.
Once the optimal conditions for glycosylation of 9 with Schmidt donor 25’ were
26
settled, they were applied to the challenging coupling of 16’ and diol acceptor 27
ACS Paragon Plus Environment

Page 11 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
(
Scheme 4). Fortunately, the reaction proceeded smoothly so that the desired 19 was
obtained in a good yield (85%), as with the Yu donor; the product was then subjected
to the conventional desilylaton conditions to yield 4 (97%). Thus far, the synthetic
route to common building block 4 featuring both high efficiency and low cost was
also established.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Scheme 4. Synthesis of 4 with glycosyl trichloroacetimidate as donors.
Although the generation of the branched trisaccharide building block 4, stepwise
with Yu donors as well as simultaneously with both Yu and Schmidt donors, has been
successfully established, the efficiency, flexibility and economy of the synthetic
strategy is finally also determined by the introduction manner of the sugar chain at the
Cꢀ19 carboxylic group. To this aim, the PTC glycosylation protocol with glycosyl
bromides as glycosyl donors was examined. The synthesis of glycosyl bromide 6
27
contained coupling of Schmidt donor 16’ with known acceptor 29 and the following
replacement of the anomeric All group of the obtained disaccharide 30 by an
alphaꢀoriented bromide via the sequence of deallylation, Oꢀacetylation and bromide
substitution (6, 71%, 3 steps, Scheme 5). Commencing with 2,3ꢀOꢀunprotected
acceptor 23 and Schmidt donor 16’ the trisaccharide 31 was obtained in 78% yield,
2
8
and no thioglycoside aglycone transfer was detected. Acidꢀmediated benzylidene
cleavage was followed by Oꢀacetylation yielding 32, which was reacted with IBr to
9
c
afford trisaccharide bromide 7 (89%).
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Scheme 5. Synthesis of diꢀ and triꢀsaccharide bromide donors 6 and 7.
With glycosyl bromide donors 5ꢀ7 and common building block 4 in hand,
investigation of the PTC glycosylation as well as the completion of the synthesis was
undertaken (Scheme 6). In the presence of tetrabutylammonium bromide (TBAB) and
29
potassium carbonate, the reaction between 4 and glucosyl bromide 5 proceeded
smoothly and the desired glucosylation product 33 (having four sugar residues
attached) was obtained in a good 85% yield. Benzylidene group cleavage with
pꢀTsOH in a mixture of methanol/dichloromethane worked very well and no
isomerization/rearrangement of the aglycone or loss of the trisaccharide residue at
Cꢀ13 was observed. Following Zemplen saponification led successfully to the target
molecule 1, rebaudienoside A (82%, 2 steps). The PTC glycosylation method was so
efficient that both, disaccharide bromide 6 and trisaccharide bromide 7, afforded good
to excellent coupling yields, providing 34 with five sugar residues (93%) and 35 with
six sugar residues (86%), respectively. Thus, after debenzylidenation and cleavage of
the acetyl and benzoyl groups furnishing both compounds in 81% yield over two steps,
a firm methodology for the efficient synthesis of the valuable rebaudiosides D (2) and
M (3) was available. The spectroscopic data of the target compounds 1ꢀ3 are in good
ACS Paragon Plus Environment

Page 13 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
3
0
accordance with those reported in the literature.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Scheme 6. Introduction of C19ꢀCOOH sugar chains via PTC protocol and completion
synthesis of all three target molecules.
Conclusions:
In summary, based on the large scale acquisition of steviol from the crude extract of S.
rebaudiana leaves, ample amounts of the aglycone were available for the first
efficient, diversityꢀoriented, and economic protocol to generate steviol glycosides.
The diversity was founded on the stepwise introduction of the sugar residues at the
Cꢀ13 hydroxy group with Yu donors and at the Cꢀ19 carboxylic group with glycosyl
bromides as glycosyl donors and the cost economy was taken care of by the
successful application of Schmidt donors in glycosidic linkage construction. The high
overall efficiency has benefited from the judicious choice of suitable glycosylation
protocols, mild Yu glycosylation, Schmidt glycosylation that could be conducted at
low temperature without any glycosylation potential loss, and PTC glycosylation,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
which all kept the fragile steviol aglycone untouched and provided good to excellent
glycosylation yields. The established synthesis strategy is obviously applicable to
other steviol glycoside congeners and derivatives, thus providing a reliable and robust
method to access these valuable natural products. Hence, a firm basis is now available
to solve the problems that so far restrict the development of stevioside industry.
Experimental Section:
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
16,17ꢀαꢀEpoxylꢀsteviol
tertꢀbutyldiphenylsilyl
ester
(8a)
and
15,16ꢀαꢀepoxylꢀsteviol tertꢀbutyldiphenylsilyl ester (8b)
To a solution of steviosides mixture (100 g) in water (250 mL) was added HCl (0.04
o
M, 0.83 mL) at room temperature. Then the reaction mixture was heated to 95 C, and
the stirring was continued for 28 h, during which time white precipitates appeared.
The precipitates were collected by filtration, and then washed thoroughly with water.
After drying under reduced pressure, the precipitates was recrystallized from absolute
MeOH to afford the crude product containing steviol, isosteviol, and double bond
migrated isomer (12.0 g) as a white solid.
The mixture obtained above (12.0 g) was dissolved in dry DMF (50 mL), to which
imidazole (3.84 g, 56.5 mmol) and TBDPSCl (14.7 mL, 56.5 mmol) was added
2
successively at room temperature under N atmosphere. The reaction mixture was
stirred at the same temperature overnight. Ethyl acetate was added to dilute the
reaction mixture, and the resultant solution was washed successively with water and
2 4
brine, and then dried over anhydrous Na SO . Filtration was followed by
concentration to afford the crude product, which was purified by silica gel
ACS Paragon Plus Environment

Page 15 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
chromatography (PE/EA = 10 : 1) to afford an inseparable mixture of silylated steviol
as well as its silylated double bond migrated isomer (12.6 g) as a white foam.
2 2
To a solution of above obtained mixture (12.6 g) in dry CH Cl (50 mL) was added
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
mꢀCPBA (5.86 g, 34.0 mmol) at 0 C. After the addition was completed, the reaction
mixture was warmed up gradually to room temperature, and the stirring was
continued at the same temperature for another 2 h. Ethyl acetate was added to dilute
the reaction mixture, and the solution was washed successively with saturated
2 2 3 2 4
aqueous Na S O and brine, and then dried over anhydrous Na SO . Filtration and
concentration under reduced pressure yielded a residue, which was further purified by
silica gel chromatography (PE/EA = 4 : 1) to afford 8a (6.62 g) as a white foam and
2
5
1
8b (6.3 g) as a white foam. For 8a: [α]
CDCl ) δ 7.69ꢀ7.66 (m, 4 H), 7.45ꢀ7.40 (m, 2 H), 7.38ꢀ7.34 (m, 4 H), 2.93 (d, J = 4.8
Hz, 1 H), 2.78 (d, J = 4.8 Hz, 1 H), 2.34 (brs, 1 H), 2.24ꢀ2.19 (m, 1 H), 2.14 (dd, J =
D
= ꢀ31.6 (c 1.0, CHCl3); H NMR (400 MHz,
3
2
3
7
2
5
.0, 11.2 Hz, 1 H), 1.35 (dd, J = 2.8, 11.2 Hz, 1 H), 1.27 (s, 3 H), 1.14 (s, 9 H), 0.76 (s,
13
3
H); C NMR (100 MHz, CDCl ) δ 176.9, 135.8 (2 C), 132.1 (2 C), 130.1, 127.7,
4.9, 65.4, 57.1, 53.9, 48.8, 46.7, 45.8, 45.2, 41.7, 41.5, 40.8, 39.5, 38.6, 34.8, 29.3,
+
7.3, 22.3, 19.7, 19.4, 19.3, 16.4, HRMS (ESI) calcd for C36
H48NaO
4
Si [M+Na]
25
D
1
95.3214, found 595.3210. For 8b: [α]
= ꢀ61.7 (c 1.0, CHCl
3
); H NMR (400 MHz,
CDCl ) δ 7.68ꢀ7.65 (m, 4 H), 7.44ꢀ7.40 (m, 2 H), 7.37ꢀ7.33 (m, 4 H), 2.71 (s, 1 H),
3
2.25ꢀ2.20 (m, 1 H), 1.91ꢀ1.87 (m, 1 H), 1.84ꢀ1.65 (m, 5 H), 1.57ꢀ1.50 (m, 3 H), 1.37
13
(
s, 3 H), 1.27 (s, 3 H), 1.13 (s, 9 H), 1.07ꢀ0.99 (m, 3 H), 0.71 (s, 3 H); C NMR (100
MHz, CDCl
3
) δ 176.7, 135.8, 135.7, 132.1, 132.0, 130.1, 127.6, 78.9, 67.2, 61.9, 61.8,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
5
6.8, 48.4, 45.3, 43.7, 40.9, 39.4, 38.7, 38.5, 36.0, 33.6, 29.3, 27.3, 21.0, 20.4, 19.7,
+
19.4, 19.2, 15.9, 11.0; HRMS (ESIꢀTOF) calcd for C36
found 595.3210.
16,17ꢀαꢀEpoxylꢀsteviol 2ꢀnapthylmethyl ester (8a’) and 15,16ꢀαꢀepoxylꢀsteviol
ꢀnapthylmethyl ester (8b’)
Similar procedure as that used for the synthesis of 8a, 8b was applied to afford 8a’
H
48
O
4
SiNa [M+Na] 595.3214,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
25
D
(3.1 g) as a white foam and 8b’ (2.9 g) as a white solid. For 8a’: [α]
= ꢀ59.3 (c 1.0,
1
CHCl
3
); H NMR (400 MHz, CDCl
3
) δ 7.86ꢀ7.83 (m, 4 H), 7.53ꢀ7.46 (m, 3 H), 5.33
(AB, 2 H), 2.92 (d, J = 4.4 Hz, 1 H), 2.78 (d, J = 4.4 Hz, 1 H), 2.32 (t, J = 1.2 Hz, 1
H), 2.26 (td, J = 3.6, 13.2 Hz, 1 H), 2.15 (dd, J = 2.0, 11.2 Hz, 1 H), 1.92ꢀ1.55 (m, 10
H), 1.48ꢀ1.42 (m, 3 H), 1.35ꢀ1.32 (m, 1 H), 1.21 (s, 3 H), 1.08ꢀ0.93 (m, 3 H), 0.83 (s,
13
3
H); C NMR (100 MHz, CDCl
3
) δ 177.2, 133.5, 133.3, 133.1, 128.4, 128.1, 127.8,
127.6, 126.4, 126.3, 126.1, 74.8, 66.4, 65.4, 57.1, 53.9, 48.8, 46.6, 45.8, 44.0, 41.7,
41.3, 40.8, 39.4, 38.1, 34.8, 29.0, 22.0, 19.6, 19.2, 15.8; HRMS (ESI) calcd for
+
25
D
C
31
H
39
O
4
[M+H] 475.2843, found 475.2849. For 8b’: [α]
) δ 7.85ꢀ7.82 (m, 4 H), 7.52ꢀ7.44 (m, 3 H), 5.31 (AB, 2 H),
.70 (s, 1 H), 2.25 (td, J = 3.2, 12.8 Hz, 1 H), 1.89ꢀ1.81 (m, 3 H), 1.78ꢀ1.62 (m, 4 H),
3
= ꢀ33.7 (c 1.0, CHCl );
1
H NMR (400 MHz, CDCl
3
2
1
13
.36 (s, 3 H), 1.22 (s, 3 H), 1.15 (dd, J = 3.2, 10.8 Hz, 1 H), 0.76 (s, 3 H); C NMR
(100 MHz, CDCl ) δ 177.2, 133.5, 133.3, 133.1, 128.4, 128.1, 127.8, 127.6, 126.4 (2
3
C), 126.2, 78.9, 67.1, 66.4, 61.8, 56.8, 48.3, 44.1, 43.7, 40.9, 39.3, 38.5, 38.1, 35.9,
+
3
3.6, 29.0, 20.7, 20.4, 19.1, 15.3, 11.0; HRMS (ESIꢀTOF) calcd for C31
39 4
H O [M+H]
475.2843, found 475.2855.
ACS Paragon Plus Environment

Page 17 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Steviol tertꢀbutyldiphenylsilyl ester (9)
To a solution of 8a (5.5 g, 9.6 mmol) in a mixed solvent of 1,4ꢀdioxane and MeOH
100 mL, v/v = 1 : 1) was added zinc dust (3.58 g, 54.8 mmol), CuSO (0.88 g, 5.5
(
4
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
mmol), NaI (2.45 g, 16.3 mmol), and NaOAc (0.82 g, 10 mmol) at room temperature.
To the resultant suspension HOAc (5.76 mL, 96 mmol) was then added. The resulting
reaction mixture was stirred at the same temperature overnight, at which time TLC
showed that all starting material disappeared. Filtration to remove all solids, and the
filtrate was diluted with ethyl acetate. The resulting solution was washed successively
with water, saturated aqueous NaHCO , and brine, then dried over anhydrous Na SO .
3
2
4
Filtration was followed by concentration under reduced pressure yielded the crude
product, which was further purified by silica gel chromatography (PE/EA = 10 : 1) to
25
1
afford 9 (5.35 g, 100%) as a white foam: [α]
MHz, CDCl ) δ 7.69ꢀ7.66 (m, 4 H), 7.45ꢀ7.34 (m, 6 H), 4.97 (t, J = 2.4 Hz, 1 H), 4.81
t, J = 2.4 Hz, 1 H), 2.25ꢀ2.16 (m, 2 H), 2.09ꢀ2.02 (m, 2 H), 1.90ꢀ1.38 (m, 12 H), 1.27
s, 3 H), 1.24 (dd, J = 2.4, 11.2 Hz, 1 H), 1.14 (s, 9 H), 1.08ꢀ1.04 (m, 1 H), 0.95 (d, J
D
3
= ꢀ55.3 (c 1.0, CHCl ); H NMR (400
3
(
(
13
=
3
8.0 Hz, 1 H), 0.76 (s, 3 H); C NMR (100 MHz, CDCl ) δ 176.9, 156.3, 135.8 (2
C), 132.2 (2 C), 130.1, 127.7, 103.0, 80.4, 57.2, 53.9, 47.6, 47.1, 45.3, 41.8, 41.6, 40.8,
39.5, 39.3, 38.7, 29.4, 27.3, 22.4, 20.6, 19.4 (2 C), 16.2; HRMS (ESIꢀTOF) calcd for
+
C H O SiNa [M+Na] 579.3265, found 579.3257.
36
48
3
Steviol 2ꢀnapthylmethyl ester (9’)
Similar procedure as that used for the synthesis of 9 was applied to get 9’ (0.97 g,
2
D
5
1
100%) as a white solid: [α]
3 3
= ꢀ51.3 (c 1.0, CHCl ); H NMR (400 MHz, CDCl ) δ
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
7
.86ꢀ7.83 (m, 4 H), 7.53ꢀ7.46 (m, 3 H), 5.32 (AB, 2 H), 4.97 (t, J = 2.4 Hz, 1 H), 4.81
(d, J = 2.4 Hz, 1 H), 2.25ꢀ2.00 (m, 4 H), 1.92ꢀ1.36 (m, 9 H), 1.25ꢀ1.21 (m, 2 H), 1.21
s, 3 H), 1.08ꢀ1.04 (dd, 1 H), 0.95 (d, J = 8.0 Hz, 1 H), 0.90ꢀ0.83 (m, 3 H), 0.80 (s, 3
(
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
13
H); C NMR (100 MHz, CDCl ) δ 177.4, 156.2, 133.6, 133.3, 133.2, 128.4, 128.1,
3
1
4
27.8, 127.6, 126.4, 126.3, 126.2, 103.0, 80.3, 66.4, 57.2, 53.8, 47.5, 47.0, 44.1, 41.8,
1.4, 40.8, 39.4, 39.3, 38.2, 29.0, 22.0, 20.5, 19.2, 15.6; HRMS (ESIꢀTOF) calcd for
+
C
31
H
39
O
3
[M+H] 459.2894, found 459.2894.
15ꢀαꢀHydroxylꢀisosteviol (10)
To a solution of 8b (123 mg, 215 mmol) in dry CH Cl (2 mL) was added PPh (84.6
2
2
3
2
mg, 0.32 mmol) and I (55.0 mg, 0.22 mmol) at room temperature. The reaction
mixture was then heated to reflux, and the stirring was continued for another 2 h.
After cooling to room temperature, the reaction mixture was diluted with ethyl acetate.
The solution was washed successively with saturated aqueous Na
2 2 3
S O , brine, and
then dried over anhydrous Na SO . Filtration was followed by concentration to afford
2
4
a residue, which was further purified by silica gel chromatography (PE/EA = 1 : 1) to
25
D
1
deliver 10 (92 mg, 75%) as a light yellow solid: [α]
NMR (400 MHz, CDCl ) δ 3.39 (d, J = 1.2 Hz, 1 H), 2.55 (dd, J = 1.6, 18.8 Hz, 1 H),
.18ꢀ2.13 (m, 2 H), 2.10ꢀ2.04 (m, 1 H), 2.00ꢀ1.94 (m, 1 H), 1.89ꢀ1.58 (m, 6 H),
.47ꢀ1.37 (m, 3 H), 1.26 (s, 3 H), 1.24ꢀ1.20 (m, 2 H), 1.14 (dd, J = 2.0, 12.0 Hz, 1 H),
3
= ꢀ80.9 (c 1.0, CHCl ); H
3
2
1
13
1.04 (s, 3 H), 0.95 (dt, J = 4.4, 13.2 Hz, 1 H), 0.80 (s, 3 H); C NMR (100 MHz,
CDCl
3
) δ 183.7, 88.6, 56.6, 54.4, 54.2, 44.4, 43.7 (2 C), 40.0, 38.4, 37.7, 35.8, 35.5,
+
31 4
29.1, 21.0, 19.9, 19.0, 15.0, 13.8; HRMS (ESIꢀTOF) calcd for C20H O [M+H]
ACS Paragon Plus Environment

Page 19 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
3
35.2217, found 335.2221.
pꢀMethoxyphenyl
ꢀOꢀlevulinoylꢀ3ꢀOꢀallylꢀ4,6ꢀOꢀbenzylideneꢀβꢀDꢀglucopyranoside (12)
To a solution of 11 (500 mg, 1.2 mmol) in dry CH Cl (5 mL) was added LevOH (560
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
mg, 0.48 mmol), DMAP (300 mg, 0.25 mmol), DIPEA (0.8 mL, 0.48 mmol), and
o
EDCI (930 mg, 0.48 mmol) at 0 C under N
2
atmosphere. The reaction mixture was
warmed up to room temperature and the stirring was continued for another 12 h. Ethyl
acetate was added to dilute the reaction mixture, and the obtained mixture was washed
successively with water, saturated aqueous NaHCO , brine, and then dried over
3
anhydrous Na
2 4
SO . Filtration was followed by concentration to afford the crude
product, which was further purified by silica gel chromatography (PE/EA = 3 : 1) to
25
1
deliver 12 (580 mg, 94%) as a white solid: [α]
(400 MHz, acetoneꢀd ) δ 7.53ꢀ7.51 (m, 2 H), 7.42ꢀ7.36 (m, 3 H), 7.06 (d, J = 8.8 Hz,
H), 6.87 (d, J = 9.2 Hz, 2 H), 5.95ꢀ5.85 (m, 1 H), 5.71 (s, 1 H), 5.27 (qd, J = 2.0,
D
3
= ꢀ15.6 (c 1.0, CHCl ); H NMR
6
2
17.2 Hz, 1 H), 5.16ꢀ5.08 (m, 3 H), 4.36ꢀ4.29 (m, 2 H), 4.20ꢀ4.14 (m, m, 1 H),
3.88ꢀ3.80 (m, 3 H), 3.78ꢀ3.72 (m, 1 H), 3.75 (s, 3 H), 2.81ꢀ2.78 (m, 2 H), 2.62 (t, J =
13
6
6.8 Hz, 2 H), 2.13 (s, 3 H); C NMR (100 MHz, acetoneꢀd ) δ 171.9, 156.5, 152.3,
138.9, 136.4, 129.6, 128.9, 127.0, 119.4, 116.4, 115.3, 101.8, 101.7, 81.9, 79.5, 73.8,
+
73.7, 69.0, 67.0, 55.8, 38.1, 28.6; HRMS (ESIꢀTOF) calcd for C H O [M+H]
28
33
9
513.2119, found 513.2125.
2ꢀOꢀLevulinoylꢀ3ꢀOꢀallylꢀ4,6ꢀOꢀbenzylideneꢀ
Dꢀglucopyranosyl
orthoꢀcyclopropylethynylbenzoate (13)
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 20 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
To a solution of 12 (1.0 g, 1.95 mmol) in a mixed solvent of toluene, acetonitrile and
o
pH 7.0 buffer (2 mL, v/v/v = 1 : 2 : 1) was added CAN (3.3 g, 5.84 mmol) at 0 C.
The stirring was continued at the same temperature for another 15 min. Ethyl acetate
was added to dilute the reaction mixture, and the solution was washed successively
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2 2 3 2 4
with saturated aqueous Na S O , water, and brine, then dried over anhydrous Na SO .
Filtration was followed by concentration to afford a residue, which was further
purified by silica gel chromatography (PE/EA = 2 : 1) to afford the hemiacetal residue
(0.79 g, 89%) as a light yellow syrup, which was used directly for the next step
without detailed characterization.
The above obtained hemiacetal intermediate (0.79 g, 1.37 mmol) was dissolved in dry
i
CH
2
Cl
2
(2 mL), to which ABzOH (0.69 g, 3.7 mmol), Pr
2
NEt (1.7 mL, 9.9 mmol),
o
DMAP (575 mg, 4.7 mmol), and EDCI (1.13 g, 5.9 mmol) were added at 0 C under
2
N atmosphere. After the addition was completed, the reaction mixture was warmed
up to room temperature, and the stirring was continued for another 6 h. Ethyl acetate
was added to dilute the reaction mixture, the resulting solution was washed with water,
brine, and dried over anhydrous Na
gave a residue, which was further purified by silica gel chromatography (PE/EA = 4 :
) to 13 (0.92 g, 82%) as a mixture of α/β isomers. An aliquot of βꢀisomer was
2 4
SO . Filtration was followed by concentration
1
25
1
isolated for detailed characterization: [α]D = ꢀ37.6 (c 0.5, CHCl ); H NMR (400
3
MHz, acetoneꢀd
6
) δ 7.89 (dd, J = 1.2, 7.6 Hz, 1 H), 7.57ꢀ7.51 (m, 4 H), 7.44ꢀ7.38 (m,
4
H), 6.04 (dd, J = 1.2, 8.4 Hz, 1 H), 5.97ꢀ5.87 (m, 1 H), 5.73 (s, 1 H), 5.29ꢀ5.23 (m, 1
H), 5.21ꢀ5.16 (m, 1 H), 5.13ꢀ5.09 (m, 1 H), 4.37ꢀ4.31 (m, 2 H), 4.24ꢀ4.18 (m, 1 H),
ACS Paragon Plus Environment

Page 21 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
3
.98 (t, J = 8.4 Hz, 1 H), 3.89ꢀ3.82 (m, 3 H), 2.75 (t, J = 6.4 Hz, 2 H), 2.57ꢀ2.54 (m, 2
13
H), 2.05 (s, 3 H), 1.58ꢀ1.52 (m, 1 H), 0.97ꢀ0.92 (m, 2 H), 0.84ꢀ0.80 (m, 2 H);
C
NMR (100 MHz, acetoneꢀd
6
) δ 172.1, 164.1, 138.8, 136.3, 134.8, 133.3, 131.5, 131.2,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
129.6, 128.9, 128.1, 127.0, 126.1, 116.5, 101.9, 100.8, 93.7, 81.8, 79.3, 74.8, 73.8,
73.0, 68.9, 67.7, 38.2, 28.6, 9.2 (2 C), 1.1; HRMS (ESIꢀTOF) calcd for C33H35O9
+
[
M+H] 575.2276, found 575.2276.
1
3ꢀOꢀ(2ꢀOꢀLevulinoylꢀ3ꢀOꢀallylꢀ4,6ꢀOꢀbenzylideneꢀβꢀ
tertꢀbutyldiphenylsilyl ester (14)
To a solution of 9 (300 mg, 0.54 mmol) and 13 (470 mg, 0.82 mmol) in dry CH Cl (2
Dꢀglucopyranosyl)ꢀsteviol
2
2
mL) was added activated powdered 4A MS under N
stirred at room temperature for 30 min, to which Ph
2
atmosphere. The suspension was
3
PAuNTf (80 mg, 0.11 mmol) was
added. After stirring at room temperature for another 4 h, 4A MS was removed by
filtration. The filtrate was concentrated under reduced pressure, and the obtained
residue was purified by silica gel chromatography (PE/EA = 5 : 1) to give 14 (480 mg,
25
D
1
92%) as a white foam: [α]
6
= ꢀ28.2 (c 1.0, CHCl3); H NMR (400 MHz, acetoneꢀd )
δ 7.76ꢀ7.71 (m, 4 H), 7.54ꢀ7.37 (m, 11 H), 5.94ꢀ5.84 (m, 1 H), 5.68 (s, 1 H), 5.26 (qd,
J = 1.6, 17.2 Hz, 1 H), 5.10ꢀ5.07 (m, 1 H), 4.93 (brs, 1 H), 4.90ꢀ4.88 (m, 2 H), 4.78 (d,
J = 2.4 Hz, 1 H), 4.31ꢀ4.26 (m, 1 H), 4.18ꢀ4.11 (m, 2 H), 3.79ꢀ3.65 (m, 3 H),
3.53ꢀ3.47 (m, 1 H), 2.90ꢀ2.48 (m, 5 H), 2.22ꢀ2.10 (m, 6 H), 2.07ꢀ2.05 (m, 2 H),
2.02ꢀ1.79 (m, 6 H), 1.68ꢀ1.34 (m, 5 H), 1.31 (s, 3 H), 1.15 (s, 9 H), 1.09 (dd, J = 4,
13
13.2 Hz, 1 H), 1.02 (d, J = 8 Hz, 1 H), 0.86 (s, 3 H); C NMR (100 MHz, acetoneꢀd
6
)
δ 177.1, 171.6, 153.6, 139.0, 136.5, 136.4 (2 C), 136.3, 132.9, 132.8, 130.9, 129.6,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 22 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
28.9, 128.4, 127.1, 127.0 (2 C), 116.3, 105.0, 101.8, 97.2, 86.3, 82.2, 79.7, 74.2, 73.6,
69.2, 66.8, 57.5, 54.4, 47.9, 45.8, 44.9, 43.1, 42.0, 41.2, 40.1, 39.1, 38.0, 37.3, 28.7,
+
2
7.4, 23.0, 20.9, 20.0, 19.7, 16.9; HRMS (ESIꢀTOF) calcd for C57
945.4968, found 945.4971.
3ꢀOꢀ(3ꢀOꢀAllylꢀ4,6ꢀOꢀbenzylideneꢀβꢀ
tertꢀbutyldiphenylsilyl ester (15)
To a solution of 14 (320 mg, 0.34 mmol) in a mixed solvent of pyridine and HOAc
73
H O10Si [M+H]
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
Dꢀglucopyranosyl)ꢀsteviol
(28.8 mL, v/v = 51 : 34) was added freshly prepared NH
2
NH
2
•HOAc (230 µL, freshly
o
prepared by mixing NH NH and HOAc with a volume ratio of 1 : 3.28) at 0 C. The
2
2
stirring was continued at the same temperature for 30 min. After quenched with
acetone, ethyl acetate was added to dilute the reaction mixture. The resulting solution
was washed successively with water, saturated NaHCO
anhydrous Na SO . Filtration was followed by concentration to yield the crude
product, which was further purified by silica gel chromatography (PE/EA = 2.5 : 1) to
3
, brine, and then dried with
2
4
25
D
1
afford 15 (251 mg, 87%) as a white foam: [α]
400 MHz, acetoneꢀd ) δ 7.77ꢀ7.71 (m, 4 H), 7.54ꢀ7.33 (m, 11 H), 5.98ꢀ5.88 (m, 1 H),
.63 (s, 1 H), 5.30 (qd, J = 1.6, 17.2 Hz, 1 H), 5.12ꢀ5.10 (m, 1 H), 5.08 (qd, J = 1.6,
= ꢀ36.8 (c 1.0, CHCl3); H NMR
(
6
5
1
1
0.4 Hz, 1 H), 4.81 (d, J = 2.0 Hz, 1 H), 4.67 (d, J = 7.6 Hz, 1 H), 4.39 (d, J = 4.4 Hz,
H), 4.37ꢀ4.26 (m, 2 H), 4.13 (dd, J = 4.8, 10.0 Hz, 1 H), 3.73 (t, J = 10.0 Hz, 1 H),
3.58ꢀ3.50 (m, 2 H), 3.42ꢀ3.36 (m, 2 H), 2.24ꢀ2.20 (m, 1 H), 2.17ꢀ2.11 (m, 2 H),
.00ꢀ1.77 (m, 5 H), 1.68ꢀ1.41 (m, 5 H), 1.31 (s, 3 H), 1.16 (s, 9 H), 1.03 (d, J = 8.4 Hz,
2
1
3
6
1 H), 0.84 (s, 3 H); C NMR (100 MHz, acetoneꢀd ) δ 177.1, 153.9, 139.2, 137.0,
ACS Paragon Plus Environment

Page 23 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
1
36.5, 136.4, 133.0, 132.9, 130.9 (2 C), 129.5, 128.8, 128.5, 128.4, 127.0, 115.8,
104.9, 101.8 (2 C), 99.6, 86.4, 82.3, 81.9, 75.5, 73.8, 69.5, 66.9, 57.6, 54.5, 48.2, 45.8,
45.1, 42.9, 42.2, 41.3, 40.2, 39.2, 37.7, 27.5, 23.1, 20.9, 20.0, 19.7, 16.9; HRMS
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
+
(ESIꢀTOF) calcd for C H O Si [M+H] 847.4600, found 847.4606.
52
67
8
13ꢀOꢀ[2ꢀOꢀ(2,3,4,6ꢀTetraꢀOꢀbenzoylꢀβꢀ
Dꢀglucopyranosyl)ꢀ3ꢀOꢀallylꢀ4,6ꢀOꢀbenzyli
deneꢀβꢀ ꢀglucopyranosyl]ꢀsteviol tertꢀbutyldiphenylsilyl ester (17)
D
Similar procedure as that used for the synthesis of 14 was applied to conduct the
coupling between monosaccharide acceptor 15 and donor 16 to deliver 17 (200 mg,
25
1
92%) as a white foam: [α]D = ꢀ14.5 (c 0.67, CHCl ); H NMR (400 MHz, acetoneꢀd )
3
6
δ 8.08 (dd, J = 1.2, 8.0 Hz, 2 H), 8.01 (dd, J = 1.2, 8.4 Hz, 2 H), 7.94 (dd, J = 1.6, 8.4
Hz, 2 H), 7.82 (dd, J = 1.6, 8.4 Hz, 2 H), 7.76ꢀ7.70 (m, 4 H), 7.65ꢀ7.55 (m, 4 H),
7.51ꢀ7.41 (m, 14 H), 7.37ꢀ7.31 (m, 5 H), 6.05ꢀ5.95 (m, 2 H), 5.82 (t, J = 9.6 Hz, 1 H),
5.61 (d, J = 8.0 Hz, 1 H), 5.60 (s, 1 H), 5.56 (dd, J = 7.6, 9.2 Hz, 1 H), 5.24ꢀ5.18 (m, 2
H), 5.09 (qd, J = 1.6, 10.4 Hz, 1 H), 4.81 (d, J = 7.2 Hz, 1 H), 4.68 (dd, J = 2.8, 12.4
Hz, 1 H), 4.65 (d, J = 2.4 Hz, 1 H), 4.59 (dd, J = 4.4, 12.0 Hz, 1 H), 4.53ꢀ4.49 (m, 1
H), 4.29ꢀ4.24 (m, 1 H), 4.10 (dd, J = 4.8, 10.0 Hz, 1 H), 4.05ꢀ4.00 (m, 1 H), 3.81 (t, J
=
7.6 Hz, 1 H), 3.70 (t, J = 10.0 Hz, 1 H), 3.63ꢀ3.55 (m, 2 H), 3.44ꢀ3.38 (m, 1 H),
2
.23 (d, J = 12.8 Hz, 1 H), 2.12 (dd, J = 2, 11.2 Hz, 1 H), 2.09 (s, 1 H), 2.05 (s, 1 H),
.02ꢀ1.34 (m, 13 H), 1.30 (s, 3 H), 1.15 (s, 9 H), 1.08 (dd, J = 5.6, 14.4 Hz, 1 H), 0.97
2
1
3
(d, J = 7.6 Hz, 1 H), 0.89ꢀ0.84 (m, 1 H), 0.81 (s, 3 H); C NMR (100 MHz,
acetoneꢀd ) δ 177.1, 166.4, 166.1, 165.8, 165.6, 154.0, 139.0, 136.7, 136.5, 136.4,
6
134.4, 134.2 (2 C), 133.9, 132.9 (2 C), 130.9 (3 C), 130.5, 130.4 (2 C), 130.2, 130.1,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 24 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
30.0, 129.5, 129.4, 129.3 (3 C), 128.8, 128.4, 127.0, 116.1, 105.2, 101.7 (2 C), 97.6,
86.0, 82.5, 82.4, 80.0, 74.4, 73.9, 73.6, 72.5, 70.5, 69.4, 66.2, 63.9, 57.6, 54.6, 47.9,
45.8, 44.7, 43.3, 42.1, 41.2, 40.1, 39.2, 37.0, 27.5, 23.0, 21.0, 20.0, 19.7, 16.9; HRMS
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ꢀ
(ESIꢀTOF) calcd for C H O Si [M+COOH] 1469.6075, found 1469.6110.
87
93 19
13ꢀOꢀ[2ꢀOꢀ(2,3,4,6ꢀTetraꢀOꢀbenzoylꢀβꢀDꢀglucopyranosyl)ꢀ4,6ꢀOꢀbenzylideneꢀβꢀDꢀ
glucopyranosyl]ꢀsteviol tertꢀbutyldiphenylsilyl ester (18)
2 2
To a solution of 17 (200 mg, 0.14 mmol) in a mixed solvent of MeOH and CH Cl (8
2 2
mL, v/v = 1 : 1) was added PdCl (7.5 mg, 0.04 mmol) at room temperature under N
atmosphere. The resulting reaction mixture was stirred at the same temperature for 1 h,
at which time TLC showed that all starting disappeared. Filtration through a pad of
Celite and silica gel was followed by concentration afford a residue, which was
further purified by silica gel chromatography (PE/EA = 2 : 1) to afford 18 (150 mg,
25
D
1
78%) as a white foam: [α]
3 6
= ꢀ5.7 (c 1.0, CHCl ); H NMR (400 MHz, acetoneꢀd ) δ
8.09 (dd, J = 1.2, 8.0 Hz, 8.02 (dd, J = 1.2, 8.4 Hz, 2 H), 7.94 (d, J = 1.2, 8.0 Hz, 2 H),
7.82 (dd, J = 1.2, 8.4 Hz, 2 H), 7.75ꢀ7.70 (m, 4 H), 7.65ꢀ7.33 (m, 23 H), 6.04 (t, J =
9.6 Hz, 1 H), 5.82 (t, J = 9.6 Hz, 1 H), 5.69 (d, J = 8.0 Hz, 1 H), 5.55 (s, 1 H), 5.54
(dd, J = 8.0, 9.6 Hz, 1 H), 5.24 (dd, J = 2.4, 4.4 Hz, 1 H), 4.93 (d, J = 3.2 Hz, 1 H),
4
.77 (d, J = 6.8 Hz, 1 H), 4.67ꢀ4.64 (m, 2 H), 4.59ꢀ4.49 (m, 2 H), 4.08 (dd, J = 4.8,
0.4 Hz, 1 H), 3.79ꢀ3.71 (m, 2 H), 3.68 (t, J = 10.0 Hz, 1 H), 3.46ꢀ3.32 (m, 2 H), 1.30
1
1
3
(s, 3 H), 1.14 (s, 9 H), 0.78 (s, 3 H); C NMR (100 MHz, acetoneꢀd
6
) δ 177.2, 166.5,
166.2, 165.9, 165.8, 154.0, 139.1, 136.5, 136.4, 134.3, 134.2, 134.0, 133.9, 133.0,
132.9, 131.0, 130.9, 130.8, 130.5, 130.4, 130.3, 130.2, 130.1, 129.6, 129.4, 129.3 (2
ACS Paragon Plus Environment

Page 25 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
C), 128.8, 128.4, 127.3, 105.1, 102.3, 102.2, 101.9, 97.6, 86.0, 82.2, 81.8, 75.2, 74.6,
73.6, 72.4, 70.6, 69.4, 66.4, 63.8, 57.6, 54.6, 47.9, 45.8, 44.8, 43.3, 42.1, 41.2, 40.1,
39.2, 37.0, 27.5, 23.1, 21.0, 20.3, 19.7, 16.9; HRMS (ESIꢀTOF) calcd for
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
+
C H O SiNa [M+Na] 1407.5683, found 1407.5683.
83
88 17
1
3ꢀOꢀ(2ꢀOꢀLevulinoylꢀ4,6ꢀOꢀbenzylideneꢀβꢀ
tertꢀbutyldiphenylsilyl ester (20)
Similar procedure as that used for the synthesis of 18 was applied to convert 14 to 20
Dꢀglucopyranosyl)ꢀsteviol
25
D
1
(300 mg, 76%) as a white foam: [α]
3
= ꢀ35.8 (c 1.0, CHCl ); H NMR (400 MHz,
CDCl ) δ 7.69ꢀ7.66 (m, 4 H), 7.52ꢀ7.35 (m, 11 H), 5.54 (s, 1 H), 4.99 (d, J = 2.4 Hz, 1
3
H), 4.98 (dd, J = 8.0, 9.2 Hz, 1 H), 4.84 (brs, 1 H), 4.72 (d, J = 8.0 Hz, 1 H), 4.24 (dd,
J = 5.2, 10.8 Hz, 1 H), 3.95 (t, J = 9.2 Hz, 1 H), 3.79 (t, J = 10.4 Hz, 1 H), 3.63 (t, J =
9.2 Hz, 1 H), 3.42ꢀ3.36 (m, 1 H), 2.84ꢀ2.75 (m, 1 H), 2.72ꢀ2.56 (m, 2 H), 2.50ꢀ2.43
(m, 1 H), 2.28 (d, J = 13.6 Hz, 1 H), 2.14 (s, 3 H), 2.03 (d, J = 17.6 Hz, 1 H),
13
1
.95ꢀ1.38 (m, 10 H), 1.26 (s, 3 H), 1.14 (s, 9 H), 1.08ꢀ0.94 (m, 3 H), 0.76 (s, 3 H); C
NMR (100 MHz, CDCl
3
) δ 207.2, 176.9, 172.0, 152.0, 137.2, 135.7 (2 C), 132.2,
1
6
2
9
30.1 (2 C), 129.4, 128.4, 127.7, 126.5, 105.2, 102.0, 96.3, 86.4, 80.7, 75.2, 72.6, 68.8,
6.4, 57.0, 53.8, 47.6, 45.3, 44.2, 42.4, 41.4, 40.7, 39.5, 38.7, 38.4, 37.1, 30.0, 29.4,
+
8.3, 27.3, 22.2, 20.4, 19.4, 16.4; HRMS (ESIꢀTOF) calcd for C54
05.4655, found 905.4642.
69
H O10Si [M+H]
13ꢀOꢀ[2ꢀOꢀLevulinoylꢀ3ꢀOꢀ(2,3,4,6ꢀtetraꢀOꢀbenzoylꢀβꢀDꢀglucopyranosyl)ꢀ4,6ꢀOꢀbe
nzylideneꢀβꢀ ꢀglucopyranosyl]ꢀsteviol tertꢀbutyldiphenylsilyl ester (21)
D
Similar procedure as that used for the synthesis of 14 was applied to conduct the
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 26 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
5
condensation of 16 and 20 to afford 21 (510 mg, 92%) as a white foam: [α]
D
= ꢀ0.9
1
(c 1.0, CHCl
3
); H NMR (400 MHz, acetoneꢀd
6
) δ 8.01 (dd, J = 1.2, 8.0 Hz, 2 H),
7
.95 (dd, J = 1.2, 8.0 Hz, 2 H), 7.88 (dd, J = 1.2, 8.4 Hz, 2 H), 7.80 (dd, J = 1.2, 8.4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Hz, 2 H), 7.75ꢀ7.70 (m, 4 H), 7.61ꢀ7.55 (m, 5 H), 7.50ꢀ7.39 (m, 14 H), 7.36ꢀ7.32 (m,
2
5
2
4
3
2
H), 7.30ꢀ7.26 (m, 2 H), 6.10ꢀ60.5 (m, 1 H), 5.74 (dd, J = 8.8, 10.4 Hz, 2 H),
.49ꢀ5.43 (m, 2 H), 4.98 (dd, J = 7.6, 8.8 Hz, 1 H), 4.86ꢀ4.84 (m, 2 H), 4.72 (d, J =
.4 Hz, 1 H), 4.55 (dd, J = 3.2, 12.0 Hz, 1 H), 4.48 (dd, J = 4.8, 12.0 Hz, 1 H),
.37ꢀ4.33 (m, 1 H), 4.30 (t, J = 9.2 Hz, 1 H), 4.14 (dd, J = 4.8, 10.4 Hz, 1 H),
.81ꢀ3.76 (m, 2 H), 3.56ꢀ3.50 (m, 1 H), 2.64ꢀ2.38 (m, 4 H), 2.24 (d, J = 13.2 Hz, 1 H),
.10 (s, 3 H), 2.09 (s, 1 H), 2.03 (d, J = 8 Hz, 2 H), 1.98ꢀ1.35 (m, 12 H) , 1.30 (m, 4
H), 1.14 (s, 9 H), 1.08 (dd, J = 4.0, 8.0 Hz, 1 H), 1.00 (d, J = 8.0 Hz, 1 H), 0.89(d, J =
13
4
.0 Hz, 1 H), 0.84 (s, 3 H); C NMR (100 MHz, acetoneꢀd
6
) δ 206.4, 177.1, 171.5,
166.4, 166.1, 165.8, 153.4, 138.9, 136.4 (2 C), 134.3, 134.2, 134.1, 133.9, 133.0,
1
1
7
2
32.9, 130.9, 130.8, 130.6, 130.5, 130.4 (2 C), 130.2, 130.1 (2 C), 129.5, 129.4, 129.3,
28.8, 128.5, 128.4, 127.2, 105.0, 101.9, 100.7, 97.1, 86.4, 80.2, 80.0, 74.4, 74.3, 73.5,
2.5, 70.9, 69.3, 67.0, 64.0, 57.5, 54.4, 48.0, 45.8, 44.8, 43.1, 42.0, 41.2, 40.1, 39.2,
8.2, 37.3, 28.5, 27.5, 23.0, 20.9, 20.0, 19.8, 17.0; HRMS (ESIꢀTOF) calcd for
+
C
88
H
98NO19Si [M+NH
4
] 1500.6497, found 1500.6491.
1
3ꢀOꢀ[3ꢀOꢀ(2,3,4,6ꢀTetraꢀOꢀbenzoylꢀβꢀ
glucopyranosyl]ꢀsteviol tertꢀbutyldiphenylsilyl ester (22)
Similar procedure as that used for the synthesis of 15 was applied to convert 21 to 22
Dꢀglucopyranosyl)ꢀ4,6ꢀOꢀbenzylideneꢀβꢀDꢀ
25
D
1
(198 mg, 82%) as a white foam: [α]
3
= ꢀ6.6 (c 1.0, CHCl ); H NMR (400 MHz,
ACS Paragon Plus Environment

Page 27 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
acetoneꢀd
6
) δ 8.04 (dd, J = 1.2, 8.4 Hz, 2 H), 7.97 (dd, J = 1.2, 8.0 Hz, 2 H), 7.92 (dd,
J = 1.2, 8.0 Hz, 2 H), 7.83 (dd, J = 1.2, 8.0 Hz, 2 H), 7.77ꢀ7.72 (m, 4 H), 7.61ꢀ7.53 (m,
H), 7.51ꢀ7.33 (m, 15 H), 7.27ꢀ7.23 (m, 3 H), 6.01 (t, J = 9.6 Hz, 1 H), 5.78 (t, J =
5
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
10.0 Hz, 1 H), 5.645 (s, 1 H), 5.638 (d, J = 8.0 Hz, 1 H), 5.56 (dd, J = 8.0, 9.2 Hz, 1
H), 5.03 (d, J = 2.8 Hz, 1 H), 4.78 (d, J = 2.4 Hz, 1 H), 4.64 (d, J = 7.6 Hz, 1 H), 4.60
(dd, J = 3.2, 12.0 Hz, 1 H), 4.54ꢀ4.49 (m, 2 H), 4.45ꢀ4.40 (m, 1 H), 4.11ꢀ4.07 (m, 1 H),
3
1
1
.74 (t, J = 10.0 Hz, 1 H), 3.63 (t, J = 9.2 Hz, 1 H), 3.45ꢀ3.36 (m, 2 H), 2.24 (d, J =
3.2 Hz, 1 H), 2.13ꢀ1.99 (m, 3 H), 1.90ꢀ1.7 (m, 13 H), 1.31 (s, 3 H), 1.16 (s, 9 H),
13
.12ꢀ1.10 (m, 1 H), 1.00 (d, J = 8.0 Hz, 1 H), 0.90ꢀ0.88 (m, 1 H), 0.85 (s, 3 H); C
) δ 177.1, 166.4, 166.1, 165.8 (2 C), 153.6, 139.0, 136.4
(2 C), 134.3, 134.2, 134.0, 133.9, 133.0, 132.9, 130.9 (2 C), 130.8, 130.7, 130.4 (3 C),
30.2, 130.1 (2 C), 129.4, 129.3, 128.7, 128.5, 128.4, 127.1, 105.0, 101.6, 101.5, 99.4,
86.6, 81.2, 79.8, 75.8, 75.7, 74.4, 73.4, 72.5, 70.8, 69.4, 67.2, 64.0, 57.5, 54.5, 48.2,
NMR (100 MHz, acetoneꢀd
6
1
45.8, 44.9, 42.8, 42.1, 41.2, 40.1, 39.2, 37.7, 27.5, 23.0, 20.9, 20.0, 19.8, 16.9; HRMS
+
(ESIꢀTOF) calcd for C83
H
88
O
17SiNa [M+Na] 1407.5683, found 1407.5692.
1
3ꢀOꢀ[2,3ꢀDiꢀOꢀ(2,3,4,6ꢀtetraꢀOꢀbenzoylꢀβꢀ
ꢀglucopyranosyl]ꢀsteviol tertꢀbutyldiphenylsilyl ester (19)
Similar procedure as that used for the synthesis of 14 was applied to conduct the
Dꢀglucopyranosyl)ꢀ4,6ꢀOꢀbenzylideneꢀ
βꢀ
D
2
5
condensation of 16 and 22 to afford 19 (212 mg, 90%) as a white foam: [α]D = +25.2
1
(c 1.0, CHCl
3
); H NMR (400 MHz, CDCl
3
) δ 8.26 (d, J = 7.6 Hz, 2 H), 8.15 (d, J =
7.6 Hz, 2 H), 7.94 (d, J = 8.0 Hz, 2 H), 7.89ꢀ7.81 (m, 9 H), 7.68ꢀ7.18 (m, 40 H), 5.88
(dd, J = 10.4, 20.8 Hz, 2 H), 5.62 (dd, J = 8.0, 10.0 Hz, 1 H), 5.50ꢀ5.43 (m, 4 H), 5.07
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 28 of 50
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
brs, 1 H), 4.93 (d, J = 7.6 Hz, 1 H), 4.82 (d, J = 7.6 Hz, 1 H), 4.63 (brs, 1 H), 4.60 (d,
J = 7.6 Hz, 1 H), 4.31ꢀ4.09 (m, 6 H), 4.01 (t, J = 8.8 Hz, 1 H), 3.86 (t, J = 7.6 Hz, 1
H), 3.69ꢀ3.60 (m, 2 H), 3.28ꢀ3.22 (m, 1 H), 2.77ꢀ2.71 (m, 1 H), 2.30 (d, J = 13.2 Hz, 1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
H), 1.99 (d, J = 11.2 Hz, 1 H), 1.90ꢀ1.73 (m, 7 H), 1.58ꢀ1.28 (m, 6 H), 1.24 (s, 3 H),
13
1
1
1
1
1
6
.14 (s, 9 H), 0.79 (s, 3 H); C NMR (100 MHz, CDCl
3
) δ 176.8, 166.0 (3 C), 165.8,
65.2, 165.1 (2 C), 152.7, 137.5, 135.7, 133.7, 133.5, 133.4, 133.3, 133.1, 133.0,
32.2, 132.1, 130.3, 130.1, 130.0, 129.8 (2 C), 129.7, 129.6, 129.5, 129.4, 129.3,
29.1, 129.0 (2 C), 128.9, 128.5, 128.4 (3 C), 128.3, 128.1, 127.7, 126.2, 105.1, 101.4,
00.2, 100.0, 97.0, 85.6, 80.6, 79.0, 78.6, 73.0, 72.8, 72.7, 71.5, 71.4, 70.2, 69.7, 68.9,
5.9, 63.5, 63.1, 60.5, 57.1, 54.0, 47.2, 45.3, 43.6, 42.9, 41.4, 40.7, 39.5, 38.8, 36.2,
115
29.4, 27.2, 22.2, 20.4, 19.5, 19.4, 16.5; HRMS (ESIꢀTOF) calcd for C117H O26Si
+
[
M+H] 1964.7473, found 1964.7485.
pꢀTolylꢀ2,3ꢀdiꢀOꢀlevulinoylꢀ4,6ꢀOꢀbenzylideneꢀ1ꢀthioꢀβꢀ
Dꢀglucopyranoside (24)
Similar procedure as that used for the synthesis of 12 was adopted to convert 23 to 24
2
D
5
1
(5.5 g, 91%) as a white solid: [α]
= ꢀ34.9 (c 1.0, CHCl
3
); H NMR (400 MHz,
acetoneꢀd
6
) δ 7.48ꢀ7.43 (m, 4 H), 7.36ꢀ7.33 (m, 3 H), 7.19 (d, J = 8.0 Hz, 2 H), 5.62 (s,
1
3
2
H), 5.42 (t, J = 8.8 Hz, 1 H), 5.04ꢀ4.95 (m, 2 H), 4.34 (dd, J = 3.6, 10.0 Hz, 1 H),
.83ꢀ3.77 (m, 1 H), 3.75ꢀ3.72 (m, 2 H), 2.83ꢀ2.79 (m, 2 H), 2.76ꢀ2.70 (m, 2 H),
13
.61ꢀ2.57 (m, 2 H), 2.54ꢀ2.49 (m, 2 H), 2.33 (s, 3 H), 2.14 (s, 3 H), 2.09 (s, 3 H); C
) δ 205.7, 205.6, 171.5, 171.1, 138.1, 137.6, 132.9, 129.7,
28.8, 128.7, 128.0, 126.3, 101.0, 100.9, 86.1, 78.1, 72.6, 70.5, 70.3, 68.0, 37.3 (2 C),
NMR (100 MHz, acetoneꢀd
6
1
+
35 9
27.8, 27.7, 25.4, 20.4, 20.3; HRMS (ESIꢀTOF) calcd for C30H O S [M+H] 571.1996,
ACS Paragon Plus Environment

Page 29 of 50
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
found 571.1995
2,3ꢀDiꢀOꢀlevulinoylꢀ4,6ꢀOꢀbenzylideneꢀ
Dꢀglucopyranosyl
orthoꢀcyclopropylethenylbenzoate (25)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
To a solution of 24 (1.0 g, 1.75 mmol) in a mixed solvent of acetone and H O (40 mL,
2
v/v = 3 : 1) was added trichloroisocyanuric acid (TCCA) (610 mg, 2.6 mmol)
o
portionwise at 0 C. After the addition was completed, filtration was followed by
dilution of the filtrate with ethyl acetate. The resulting solution was washed
successively with water, saturated aqueous NaHCO
3
, brine, and then dried over
Na SO . Filtration was followed by concentration in vacuo gave a residue, which was
2
4
further purified by silica gel chromatography (PE/EA = 1 : 1) to afford hemiacetal
intermediate. The hemiacetal intermediate was used for Yu donor preparation without
further characterization. Under the standard conditions, the hemiacetal compound was
efficiently converted to Yu donor 25 (1.0 g, 90% for 2 steps) as a mixture of α/β
25
isomers. An aliquot of pure βꢀisomer was obtained for detailed characterization: [α]D
1
=
ꢀ41.4 (c 1.0, CHCl
3
); H NMR (400 MHz, CDCl
3
) δ 7.93 (dd, J = 1.2, 8.0 Hz, 2 H),
7.50ꢀ7.43 (m, 4 H), 7.38ꢀ7.29 (m, 4 H), 6.02 (d, J = 8.0 Hz, 1 H), 5.52 (s, 1 H), 5.49 (t,
J = 8.8 Hz, 1 H), 5.36 (dd, J = 8.0, 9.2 Hz, 1 H), 4.44 (dd, J = 3.6, 9.6 Hz, 1 H),
3
0
.83ꢀ3.72 (m, 3 H), 2.86ꢀ2.44 (m, 8 H), 2.15 (s, 3 H), 2.08 (s, 3 H), 1.58ꢀ1.51 (m, 1 H),
1
3
.94ꢀ0.89 (m, 4 H); C NMR (100 MHz, CDCl ) δ 206.5, 206.1, 171.9, 171.6, 163.4,
3
136.8, 134.6, 132.7, 131.0, 129.3 (2 C), 128.4, 128.3, 127.3, 126.3, 126.0, 101.7,
100.7, 92.8, 78.4, 74.4, 71.6, 71.0, 68.5, 67.3, 38.0, 37.9, 29.9, 29.7, 28.0 (2 C), 9.2,
+
9.1, 0.9; HRMS (ESIꢀTOF) calcd for C35
H
37
O
11 [M+H] 633.2330, found 633.2337.
ACS Paragon Plus Environment