Facile synthesis of saikosaponins

molecules

Article

Facile Synthesis of Saikosaponins

Ziqiang Wang ¹, Bingcheng Wei ², Tong Mu ², Peng Xu ^2,3,* and Biao Yu ^2,3,

*

1

Department of Chemistry, University of Science and Technology of China, 96 Jinzhai Road,

Hefei 230026, China; 18355122023@163.com

State Key Laboratory of Bio-organic and Natural Products Chemistry,

Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry,

Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China; weibc@sioc.ac.cn (B.W.);

mutong@sioc.ac.cn (T.M.)

School of Chemistry and Materials Science, Hangzhou Institute for Advanced Study,

University of Chinese Academy of Sciences, 1 Sub-lane Xiangshan, Hangzhou 310024, China

Correspondence: peterxu@sioc.ac.cn (P.X.); byu@sioc.ac.cn (B.Y.)

2

3

*

Abstract: Saikosaponin A (SSa) and D (SSd) are typical oleanane-type saponins featuring a unique

13,28-epoxy-ether moiety at D ring of the aglycones, which exhibit a wide range of biological and

pharmacological activities. Herein, we report the ﬁrst synthesis of saikosaponin A/D (

their natural congeners, including prosaikosaponin F ( ), G ( ), saikosaponin Y ( ), prosaikogenin

), and clinoposaponin I ( ). The present synthesis features ready preparation of the aglycones

of high oxidation state from oleanolic acid, regioselective glycosylation to construct the -(1 3)-

1–2) and

3

4

5

(6

7

β

→

linked disaccharide fragment, and efﬁcient gold(I)-catalyzed glycosylation to install the glycans on to

the aglycones.

Keywords: saikosaponin; triterpene; glycoside; glycosylation; gold(I)

ꢀꢁꢂꢀꢃꢄꢅꢆꢇ

ꢀꢁꢂꢃꢄꢅꢆ

Citation: Wang, Z.; Wei, B.; Mu, T.;

Xu, P.; Yu, B. Facile Synthesis of

Saikosaponins. Molecules 2021, 26,

1941. https://doi.org/10.3390/

molecules26071941

1. Introduction

The roots of Radix Bupleuri, one of the most common traditional Chinese medicines,

have been frequently used for the treatment of common cold with fever, inﬂuenza, inﬂam-

mation, and infectious diseases [

compounds in Radix Bupleuri and are used as the markers for evaluation of the quality of

the medicine (Figure 1) [ ]. Indeed, these two triterpene glycosides together with their

1,2]. Saikosaponin A (SSa, 1) and D (SSd, 2) are the major

Academic Editor: Amélia Pilar Rauter

3

congeners exhibit a variety of pharmacological activities, including anti-inﬂammatory, anti-

tumor, neuro-regulation, immuno-regulation, hepatoprotection, and antiviral effects [1,4].

Structurally, SSa (1) and SSd (2) are a pair of the oleanane-type disaccharide stereoisomers,

with the aglycones, namely saikogenin F (SGF) and saikogenin G (SGG), respectively,

featuring a 13,28-epoxy-ether moiety at the D ring and an opposite chirality at 16-OH.

Received: 18 February 2021

Accepted: 10 March 2021

Published: 30 March 2021

Publisher’s Note: MDPI stays neutral

with regard to jurisdictional claims in

published maps and institutional afﬁl-

iations.

Interestingly, SSa (

) showed a strong antitumor effect [

saikogenin F (PSF, ) and G (PSG, ) were identiﬁed as metabolites of SSa and SSd [

showed hemolytic activity and the absorbability on red blood cells [ ]. Saikosaponin

Y ( ) is likely a biogenetic precursor/product of SSa and SSd, which has a higher oxida-

tion state at C-16; this congener displayed potent cytotoxic and antiviral activities [ 10].

Monosaccharide , named posaikogenin, was found as an artifact which might be derived

from disaccharide . A number of saikosaponin-like compounds have also been identiﬁed

from Clinopodium gracile and other plants, among which Clinoposaponin I ( ) bearing a

trisaccharide residue is a typical one [11 13]. All these seven saponins ( ) belong to type

1

) was reported to show a strong anti-inﬂammatory effect, whereas SSd

]. The corresponding monosaccharides, named pro-

], which

(2

1

3

4

5

6,7

5

8–

6

Copyright:

5

Licensee MDPI, Basel, Switzerland.

This article is an open access article

distributed under the terms and

conditions of the Creative Commons

Attribution (CC BY) license (https://

creativecommons.org/licenses/by/

4.0/).

7

–

1–7

I saikosaponins, which bear the 13,28-epoxy-ether moiety, and this epoxy-ether moiety is

found crucial to their cytotoxic activities.

Molecules 2021, 26, 1941. https://doi.org/10.3390/molecules26071941

https://ww w .mdpi.com/journal/molecules

Molecules 2021, 26, 1941

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Figure 1. Saikosaponin A (1), D (2), and congeners (3–7).

Notwithstanding, these naturally extracted saikosaponins are associated with systemic

toxicities and side effects [14 15]. Thus, saikosaponins could induce obvious hepatoxicity

and necrosis upon 15 day administration to rats [14]. Furthermore, SSd ( ) alone was found

,

2

to stimulate mitochondrial apoptosis in human hepatocyte cells [15]. On the other hand,

these saikosaponins are difﬁcult to purify from plants; therefore, in-depth studies have

not been carried out on their structure-activity relationship (SAR) and mode of action.

Chemical synthesis of saikosaponins is also a challenging task, given the scarce availability

of the triterpene aglycones that bear high oxidation state at the D/E rings [16

recently, we disclosed a site-selective C-H hydroxylation reaction at the D/E rings of

pentacyclic triterpenoids, thus paving a venue for the synthesis of saikosaponins [18 20].

Herein, we report the synthesis of saikosaponin A ( ), D ( ), and their congeners ( ),

–19]. Very

,

1

2

3–7

using the largely available oleanolic acid as a starting material.

2. Results

We envisioned the assembly of saikosaponins (1–7) from two pieces, i.e., a saikogenin

derivative and a glycosyl donor (Scheme 1) [21]. Considering the susceptibility of the 13,28-

epoxy-ether moiety in the aglycones, we planned to employ glycosyl o-alkynylbenzoates

as donors that can proceed glycosylation under the mild gold(I)-catalyzed conditions.

Scheme 1. Retrosynthetic plan for saikosaponins 1–7.

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The requisite disaccharide o-alkynylbenzoates 11 and 12 were readily prepared via a

regioselective glycosylation approach (Scheme 2) [22]. In view of the higher reactivity of

the equatorial 3-OH versus the equatorial 2-OH and the axial 4-OH in p-methoxyphenyl

β-D-fucopyranoside

9

, condensation of triol

9

with glucosyl bromide

8

under the modi-

ﬁed Taylor’s conditions led to the desired (1

Acetylation of diol 10, oxidative cleavage of the anomeric MP group with CAN, and es-

teriﬁcation with o-alkynylbenzoic acid furnished disaccharide o-alkynylbenzoate 11 (75%

→

3)-disaccharide 10 smoothly (85%) [23

,

24].

for 3 steps) [25,26]. Since the 2-O-acetyl group might result in orthoester formation or

migration to the aglycone during the glycosylation reactions [27–29], 2,4-di-O-benzoyl

o-alkynylbenzoate 12 was also prepared (77% for 3 steps).

Scheme 2. Preparation of disaccharide o-alkynylbenzoates 11 and 12.

The synthesis of saikogenins commenced with known compound 13, which was

readily prepared from oleanolic acid in 7 steps (Scheme 3) [20]. Desilylation with the

Olah reagent, oxidation of the resultant 3-OH, and subsequent oxime formation with

hydroxylamine hydrochloride afforded oxime 14 (84%). It was noted that desilylation

with TBAF under reﬂux conditions led to unmask of the 16-O-acetyl group. Selective

hydroxylation of the C-4 equatorial methyl group was then achieved following Baldwin’s

method to furnish 15 (63%) [30–34]. that involved (1) cyclopalladation of the equatorial

methyl group from oxime 14 with Na₂PdCl₄, (2) acetylation of the oxime hydroxyl group,

and (3) oxidation with Pb(OAc)₄followed by reductive workup with NaBH₄. Hydrolysis

of 15 under basic conditions and then with TiCl₃/NH₄OAc gave 3-one-16-

nascent 16- -OH and 23-OH were ﬁrstly protected with acetyl groups; however, subsequent

reduction of the 3-ketone with NaBH₄led to a mixture, due to acetyl group migration

under basic conditions [35 36]. Thus, diol 16 was masked with the bulkier pivaloyl groups

β-ol 16. The

β

,

and then the carbonyl was reduced with NaBH₄to afford the desired aglycone derivative

17 (80%) [37].

Scheme 3. Preparation of aglycone derivative 17.

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As expected, condensation of 17 with disaccharide o-alkynylbenzoate 11 proceeded

smoothly under the catalysis of PPh₃AuNTf₂(0.1 equiv.) [38], leading to glycoside 18 (84%)

(Scheme 4). Alternatively, coupling of 17 with a relevant disaccharide trichloroacetimidate

under the promotion of TMSOTf (0.1 equiv.) failed to provide glycoside 18, due to decom-

position of 17 under the acidic conditions [5,39]. Finally, saponiﬁcation of 18 under basic

and reﬂux conditions furnished SSa (1) in 93% yield [40].

Scheme 4. Gold(I)-catalyzed glycosylation and synthesis of saikosaponin A (1).

SSd (

2

) could be synthesized by modiﬁcation of the synthetic approach to SSa (

1)

(Scheme 5). Thus, the conﬁguration of 16-β-OH in 16 was inverted via Dess-Martin oxida-

tion and NaBH₄reduction, giving SGG (19) in good yield (65%). Selective protection of

the primary 23-OH with pivaloyl group provide diol 20 (81%). It was reported that regios-

elective acetylation of the triterpene C3-OH in the presence of C16-OH was feasible [41].

Thus, we attempted a regioselective glycosylation of 3,16-diol 20. Disappointingly, the

glycosylation reactions with disaccharide donors 11 and 12 were found to futile, leading to

complex mixtures.

Scheme 5. An attempt at glycosylation of diol 20.

Considering the inﬂuence of the 16-α-OH on the 3-O-glycosylation, we arranged the

reduction of 16-ketone at a late stage (Scheme 6). Thus, the 3-ketone in 16 was reduced

with Me₄NBH(OAc)₃[42,43], the resultant 3,23-diol was then protected with silylidene

ketal, subsequent Dess-Martin oxidation of the remaining 16-OH led to ketone 21 (74% for

3 steps). Next, the silylidene ketal in 21 was removed and the resulting primary 23-OH

was selectively protected with pivaloyl group to furnish 22 (81%). Coupling of 3-ol 22

with disaccharide o-alkynylbenzoate 11 under the optimized gold(I)-catalyzed conditions

provided the desired glycoside 23 in excellent yield (95%). Ketone 23 was then subjected to

reduction with NaBH₄followed by saponiﬁcation with KOH at 55 ^◦C to afford SSd (

2) in

74% yield. Direct saponiﬁcation of 23 furnished saikosaponin Y (5) (94%).

Molecules 2021, 26, 1941

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Scheme 6. Synthesis of saikosaponin D (2) and saikosaponin Y (5).

To synthesize monosaccharide saikosaponins

3,

4, and

6, fucosyl o-alkynylbenzoate

24 was prepared from p-methoxyphenyl -D-fucopyranoside

β

9 via protection with ben-

zoyl groups, oxidative cleavage of the anomeric MP group, and esteriﬁcation with o-

alkynylbenzoic acid (79% for 3 steps) (Scheme 7). Glycosylation of aglycone derivatives 17

and 22 with o-alkynylbenzoate 24 led to glycosides 25 (91%) and 26 (84%). Saponiﬁcation

of 25 and 26 afforded prosaikogenin F (3) and prosaikogenin 6 in good yields. Alter-

natively, reduction of the 16-ketone in 26 with NaBH₄prior to saponiﬁcation furnished

prosaikogenin G (4) in 79% yield.

Scheme 7. Synthesis of prosaikosaponin F (3), G (4), and prosaikogenin (6).

The synthesis of trisaccharide clinoposaponin I (7) was depicted in Scheme 8. Removal

of the acetyl groups on disaccharide 10 followed by selective tritylation of the primary

hydroxyl group and subsequent benzoylation led to disaccharide 27 (97%). Trityl ether

27 was successfully glycosylated_◦with glucosyl trichloroacetimidate 28 under the action

of TfOH (4 Å MS, CH₂Cl₂,

−

20 C), affording trisaccharide 29 in 74% yield. Oxidative

cleavage of the anomeric MP group on 29 followed by esteriﬁcation provided the desired

trisaccharide o-alkynylbenzoate 30 (81%). Under similar conditions as used in the previous

glycosylations with mono- and disaccharide donors, coupling of aglycone 17 with trisac-

charide o-alkynylbenzoate 30 led to the desired glycoside 31 in good yield (79%). Finally,

saponiﬁcation of 31 furnished clinoposaponin I (7) in 89% yield.

Molecules 2021, 26, 1941

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Scheme 8. Synthesis of clinoposaponin I (7).

The analytical data of the synthetic saikosaponins

1–7

were in good agreement with

those reported in the literatures for the natural products.

3. Experimental Section

3.1. General Information

Commercial reagents were used without further puriﬁcation and made in China unless

speciﬁed. Crushed 4Å molecular sieves (MS) were activated through ﬂame-drying under

high vacuum immediately prior to use. Dry CH₂Cl₂, DMF, and toluene were obtained by

drying with activated MS. Dry pyridine and NEt₃were obtained by drying with anhydrous

KOH. Anhydrous THF was obtained by reﬂuxing with Na under argon. Thin layer chro-

matography (TLC) was performed on TLC silica gel 60 F254 (Merck, Darmstadt, Germany).

The TLC plates were visualized with UV light and/or by staining with EtOH/H₂SO₄

(10%, v/v). Flash column chromatography was performed on silica gel SiliaFlash P60

(

40−63 µm, Silicycle, Quebec, QC, Canada). NMR spectra were measured on a Bruker

◦

AM 400 (Switzerland), Agilent 500, or 600 MHz (U.S.) NMR spectrometer at 25 C. ¹H

and ¹³C NMR signals were calibrated to the residual proton and carbon resonance of the

solvent (CDCl₃:

δ

H = 7.26 ppm,

δC = 77.16 ppm; CD₃OD: δH = 3.31 ppm, δC = 49.00 ppm;

DMSO-d6: H = 2.50 ppm,

δ

C = 39.52 ppm). High-resolution mass spectra were recorded

with Shimadzu Biotech Axima Performance FTMS, maXis 4G FTMS, Thermo Scientiﬁc Q

Exactive HF Orbitrap-FTMS, or Agilent-TOF/LC-MS 1260-6230 FTMS. Optical rotations

were measured on an Anton Paar MCP5500 polarimeter.

3.2. Synthesis of Compounds 1–7, 10–12, 14–27, and 29–31

3.2.1. Synthesis of Compound 10

2,3,4,6-Tetra-O-acetyl-

α-D-glucopyranosyl bromide 8 (115 mg, 0.3 mmol), compound

9

(50 mg, 0.2 mmol), silver(I) oxide (65 mg, 0.3 mmol), and 2-aminoethyl diphenylborinate

(9 mg, 0.04 mmol) were added to an oven-dried round bottom ﬂask under an argon

atmosphere. Dry acetonitrile (1 mL) was added and the resulting mixture was stirred at

room temperature. After 60 h, the reaction was quenched with a few drops of methanol, and

the resulting mixture was diluted with CH₂Cl₂and ﬁltered through a plug of Celite. The

crude product was puriﬁed by silica gel chromatography (petroleum ether/EtOAc = 2/1

)

to give compound 10 (76 mg, 85%) as a white foam. R_f= 0.2 (silica, PE/EtOAc = 1:1);

1

[

α]²_D⁵= 82.8 (c = 1.0, CHCl₃); H NMR (500 MHz,CDCl₃):

δ

7.08–6.93 (m, 2H), 6.87–6.75

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(m, 2H), 5.41 (d, J = 4.1 Hz, 1H), 5.26 (m, 1H), 5.10–5.02 (m, 2H), 4.86 (d, J = 7.9 Hz, 1H),

4.24–4.20(m, 1H), 4.19–4.04 (m, 3H), 3.97 (m, 1H), 3.90 (s, 1H), 3.77 (d, J = 3.6 Hz, 1H),

3.76 (s, 3H), 2.08 (s, 3H), 2.07 (s,3H), 2.03 (s, 3H), 2.02 (s, 3H), 1.27 (d, J = 6.4 Hz, 3H). ¹³

C

NMR (125 MHz, CDCl₃):

δ 170.58, 170.18, 169.88, 169.41, 118.13, 114.64, 101.59, 98.42, 81.23,

72.30, 71.90, 71.40, 70.99, 68.46, 67.53, 66.19, 61.96, 55.62, 20.74, 20.69, 20.60, 20.57, 16.18.

ESI-HRMS (m/z) calcd for C₂₇H₃₆NaO₁₅[M + Na]⁺623.1946, found 623.1951.

3.2.2. Synthesis of Compound 11

To a solution of compound 10 (63 mg, 0.1 mmol) in pyridine (1 mL), Ac₂O (0.1 mL,

1.05 mmol) and DMAP (15 mg, 0.03 mmol) were added. The mixture was stirred at room

temperature for 8 h before it was quenched with NaHCO₃and extracted with EtOAc.

The combined organic phases were washed with brine, dried over anhydrous Na₂SO₄,

ﬁltered, and concentrated under vacuum. The residue was puriﬁed by ﬂash column

chromatography on silica gel (petroleum ether/EtOAc = 1/1) to give the corresponding

acetylated product (73 mg, 96%) as a white solid.

To a stirred solution of the above product (50 mg, 0.07 mmol) in CH₃CN/H₂O

(

0.8 mL/0.2 mL), ceric ammonium nitrate (CAN) (89 mg, 0.16 mmol) was added. The

mixture was stirred at room temperature for 2 h before it was quenched with Na₂S₂O₃and

extracted with EtOAc. The combined organic phases were washed with brine, dried over

anhydrous Na₂SO₄, ﬁltered, and concentrated under vacuum. The residue was puriﬁed

by ﬂash column chromatography (petroleum ether/EtOAc, 1:1) to give the corresponding

lactol product (33 mg, 80%) as an orange foam. The α/β anomers were difﬁcult to separate.

The lactol (40 mg, 0.07 mmol), ortho-(cyclopropylethynyl) benzoic acid (18 mg, 0.09 mmol),

EDCI (24 mg, 0.09mmol), and DMAP (12 mg, 0.09 mmol) were dissolved in CH₂Cl₂(2 mL).

The mixture was stirred at room temperature for 4 h and concentrated under vacuum. The

residue was purified by flash chromatography (petroleum ether/EtOAc = 3:1) to give com-

pound 11 (50 mg, 98%; α/β = 1:2.5) as a white foam.

11α: R_f= 0.3 (silica, PE/EtOAc = 1:1); [α]_D²⁵

=

−

3.3 (c = 1.0, CHCl₃); ¹H NMR (500 MHz

7.94 (d, 1H), 7.55–7.44 (m, 2H), 7.42–7.30 (m, 1H), 6.56 (d, J = 3.6 Hz, 1H), 5.42 (d,

,

CDCl₃):

δ

J = 3.5 Hz, 1H), 5.37 (dd, J = 10.4, 3.6 Hz, 1H), 5.16–5.03 (m, 2H), 4.91 (dd, J = 9.4, 7.9 Hz,

1H), 4.69 (d, J = 7.9 Hz, 1H), 4.52 (q, J = 6.5 Hz, 1H), 4.37 (dd, J = 10.4, 3.5 Hz, 1H), 4.23 (m,

1H), 4.15 (m, 1H), 3.68 (m, 1H), 2.16 (s, 3H), 2.10 (s, 3H), 2.06 (s, 3H), 2.00 (s, 3H), 1.98 (s,

3H), 1.95 (s, 3H), 1.18 (d, J = 6.5 Hz, 3H), 1.0–0.8 (m, 4H). ¹³C NMR (125 MHz, CDCl₃):

δ

172.30, 170.92, 170.57, 170.45, 169.99, 169.45, 169.10, 164.64, 135.12, 132.37, 131.02, 127.50,

124.77, 75.18, 72.65, 72.54, 71.97, 71.40, 69.29, 68.63, 68.25, 61.53, 20.87, 20.77, 20.73, 20.72,

20.52, 16.28, 9.18, 9.16.

1

11β: R_f= 0.25 (silica, PE/EtOAc = 1:1); [α]_D²⁵

=

−

80.5 (c = 1.0, CHCl₃); H NMR

(

500 MHz, CDCl₃): δ 7.93 (d, J = 7.9 Hz, 1H), 7.46 (d, J = 7.6 Hz, 1H), 7.41 (t, J = 7.5 Hz,

1H), 7.28 (m, 1H), 5.82 (d, J = 8.3 Hz, 1H), 5.41 (t, J = 8.7 Hz, 1H), 5.30 (s, 1H), 5.10 (m, 2H),

4.91 (t, J = 8.4 Hz, 1H), 4.62 (d, J = 7.8 Hz, 1H), 4.26 (m, 1H), 4.15 (m, 1H), 3.94 (m, 2H),

3.69–3.58 (m, 1H), 2.15 (s, 3H), 2.10 (s, 3H), 1.99 (s, 9H), 1.97 (s, 3H), 1.51 (m, 1H), 1.20 (d,

J = 5.3 Hz, 3H), 0.89 (m, 4H). ¹³C NMR (125 MHz, CDCl₃):

δ 170.84, 170.43, 170.41, 169.37,

169.32, 169.16, 163.64, 134.53, 132.58, 131.04, 129.35, 127.23, 125.79, 100.76, 100.45, 92.44,

74.46, 72.60, 71.95, 71.62, 71.19, 70.90, 70.00, 68.25, 61.43, 20.88, 20.76, 20.68, 20.48, 16.20,

9.02. ESI-HRMS (m/z) calcd for C₃₆H₄₂NaO₁₇[M + Na]⁺769.2314, found 7769.2311.

3.2.3. Synthesis of Compound 12

To a stirred solution of compound 10 (830 mg, 1.4 mmol) in pyridine (5 mL), benzoyl

chloride (0.48 mL, 4.14 mmol) and DMAP (50 mg, 0.4 mmol) were added. The mixture was

stirred at room temperature for 8 h before it was quenched with NaHCO₃and extracted

with EtOAc. The combined organic phases were washed with brine, dried over anhydrous

Na₂SO₄, and ﬁltered. The ﬁltrate was concentrated under vacuum. The residue was

puriﬁed by ﬂash column chromatography on silica gel (petroleum ether/EtOAc = 3/1) to

give the corresponding benzoylated product (1.07 g, 96%) as a white solid.

Molecules 2021, 26, 1941

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To a stirred solution of the above product (800 mg, 0.99 mmol) in CH₃CN/H₂O

12 mL/3 mL), ceric ammonium nitrate (1.35 g, 2.5 mmol) was added. The mixture was

(

stirred at room temperature for 2 h before it was quenched with Na₂S₂O₃and extracted

with EtOAc. The combined organic phases were washed with brine, dried over anhydrous

Na₂SO₄, ﬁltered, and concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography (petroleum ether/EtOAc = 1:1) to give the corresponding lactol

product (560 mg, 81%) as an orange foam. The α/β anomers were difﬁcult to separate.

The lactol (400 mg, 0.07 mmol), ortho-(cyclopropylethynyl) benzoic acid (167 mg,

0.89 mmol), EDCI (172 mg, 0.89 mmol), and DMAP (110 mg, 0.89 mmol) were dissolved

in CH₂Cl₂(5 mL). The mixture was stirred at room temperature for 4 h and then con-

centrated under vacuum. The residue was puriﬁed by ﬂash chromatography (petroleum

ether/EtOAc = 3:1) to give compound 12 (552 mg, 99%; α/β = 1:2.3) as a white foam.

12α: R_f= 0.2 (silica, PE/EtOAc = 3:1); [α]²_D⁵= 107.9 (c = 1.0, CHCl₃); ¹H NMR (500 MHz

CDCl₃): 8.11 (d, J = 7.5 Hz, 2H), 7.94 (d, J = 7.6 Hz, 2H), 7.90 (d, J = 7.8 Hz, 1H), 7.66–7.44

,

δ

(m, 6H), 7.37 (m, 3H), 6.79 (d, J = 3.5 Hz, 1H), 5.84 (m, 1H), 5.75 (d, J = 2.5 Hz, 1H), 5.05–4.92

(m, 2H), 4.78 (m, 2H), 4.72–4.57 (m, 2H), 4.14 (m, 2H), 3.65 (m, 1H), 2.01 (s, 3H), 1.96 (s, 3H),

1.85 (s, 3H), 1.44 (m, 1H), 1.36 (s, 3H), 1.31–1.24 (m, 3H), 0.87 (m, 4H). ¹³C NMR (125 MHz,

CDCl₃):

δ 170.90, 170.32, 169.32, 168.83, 166.02, 165.43, 164.59, 135.00, 133.62, 133.31, 132.32,

131.06, 130.95, 130.14, 129.83, 129.79, 129.29, 128.68, 128.60, 127.44, 124.76, 100.92, 99.57,

91.39, 75.07, 74.29, 73.08, 72.75, 71.85, 71.22, 69.36, 68.88, 68.15, 61.60, 20.80, 20.69, 20.60,

19.75, 16.66, 9.24, 9.19.

12β: R_f= 0.15 (silica, PE/EtOAc = 3:1); [α]²_D⁵= 47.7 (c = 1.0, CHCl₃); ¹H NMR (500 MHz

,

CDCl₃):

δ 8.13 (d, J = 7.5 Hz, 2H), 7.97 (d, J = 7.6 Hz, 2H), 7.93 (d, J = 7.9 Hz, 1H), 7.57 (dt,

J = 22.9, 7.4 Hz, 2H), 7.49 (t, J = 7.6 Hz, 2H), 7.41 (q, J = 7.7 Hz, 3H), 7.36 (m, 1H), 7.22 (d,

J = 7.4 Hz, 1H), 6.10 (d, J = 8.4 Hz, 1H), 5.93–5.83 (m, 1H), 5.64 (d, J = 3.2 Hz, 1H), 5.03–4.93

(m, 2H), 4.79 (m, 1H), 4.67 (d, J = 7.8 Hz, 1H), 4.22 (m, 1H), 4.13 (m, 1H), 3.63 (d, J = 8.5 Hz,

1H), 2.02 (s, 3H), 1.96 (s, 3H), 1.86 (s, 3H), 1.50 (m, 1H), 1.44 (s, 3H), 1.32 (d, J = 6.3 Hz, 3H),

0.85 (m, 4H). ¹³C NMR (125 MHz, CDCl₃):

δ 170.91, 170.35, 169.32, 168.93, 166.14, 165.10,

163.84, 134.44, 133.63, 133.27, 132.48, 131.09, 130.23, 129.81, 129.48, 129.32, 128.71, 128.53,

127.20, 125.76, 110.13, 101.15, 100.42, 92.71, 78.23, 74.46, 72.78, 72.53, 71.86, 71.46, 71.12,

70.33, 68.08, 61.47, 31.75, 29.77, 20.82, 20.67, 20.60, 19.79, 16.65. ESI-HRMS (m/z) calcd for

C₄₆H₄₆NaO₁₇[M + Na]⁺893.2627, found 893.2632.

3.2.4. Synthesis of Compound 14

Compound 13 (100 mg, 0.17 mmol) was dissolved in pyridine (5 mL), to which was

added HF

pyr (0.2 mL) at room temperature. After stirring at 90 ^◦C for 24 h, the mixture

·

was quenched with saturated NaHCO₃and extracted with EtOAc. The combined organic

phases were washed with brine, dried over anhydrous Na₂SO₄, ﬁltered, and concentrated

under vacuum. The residue was puriﬁed by ﬂash column chromatography (petroleum

ether/EtOAc = 2:1) to give the 3-ol product (76 mg, 88%) as a white foam. R_f= 0.2 (silica,

PE/EtOAc = 5:1).

The above product (3.6 g, 7.2 mmol) was dissolved in CH₂Cl₂(40 mL), to which

Dess-Martin periodinane (DMP) (3.7 g, 8.6 mmol) was added. After being stirred for

2 h at room temperature, the reaction mixture was quenched with a saturated aqueous

Na₂S₂O₃solution, and the aqueous phase was extracted with CH₂Cl₂. The combined

organic extracts were dried over anhydrous Na₂SO₄and concentrated in vacuo.

The crude product was dissolved in MeOH/CH₂Cl₂(80 mL/40 mL), to which NH₂OH HCl

·

(692 mg, 10.8 mmol) and NaOAc (1.76 g, 21.6 mmol) were added at room temperature.

After stirring two hours at reflux, the reaction mixture was diluted by addition of brine,

then extracted with CH₂Cl₂. The extract was dried over anhydrous Na₂SO₄, followed by

filtration and concentration in vacuo. The residue was purified by silica gel flash column

chromatography (petroleum ether/EtOAc = 6/1 to 3/1) to give compound 14 (3.55 g, 96%)

1

as a white foam. R_f= 0.5 (silica, PE/EtOAc = 2:1); [α]²_D⁵= 76.7 (c = 1.0, CHCl₃); H NMR

(500 MHz, CDCl₃): δ 9.30–9.23 (m, 1H), 5.88–5.86 (m, 1H), 5.43–5.38 (m, 2H), 3.97 (d, J = 7.4 Hz,

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1H), 3.18 (d, J = 7.6, 1H), 3.11–3.07 (m, 1H), 2.26–2.19 (m, 1H), 2.04 (s, 3H), 1.14 (s, 3H), 1.10

(s, 3H), 1.03 (s, 3H), 1.00 (s, 3H), 0.99 (s, 3H), 0.96 (s, 3H), 0.88 (s, 3H). ¹³C NMR (125 MHz,

CDCl₃):

δ 170.80, 166.65, 132.60, 129.92, 83.88, 73.24, 68.79, 55.34, 52.16, 51.68, 45.34, 45.27,

41.88, 40.61, 38.39, 37.41, 36.51, 34.28, 33.44, 31.97, 31.52, 31.12, 26.95, 25.44, 23.76, 22.66, 21.34,

20.47, 19.43, 18.34, 17.37, 16.94. ESI-HRMS (m/z) calcd for C₃₂H₅₀NO₄[M + H]⁺512.3734,

found 512.3739.

3.2.5. Synthesis of Compound 15

To a solution of compound 14 (1.9 g, 3.62 mmol) in HOAc (170 mL), NaOAc (350 mg,

4.3 mmol) and Na₂PdCl₄(1.3 g, 4.3 mmol) were added at room temperature. The mixture

was stirred at room temperature for 3 d, and then ice water (300 mL) was added. The

resulting mixture was stirred for an additional 20 min and then ﬁltered. The ﬁltered residue

was washed with water several times, dried, and used without further puriﬁcation.

The residue was dissolved in CH₂Cl₂(20 mL) at room temperature, to which NEt₃

(

1 mL, 7.24 mmol), DMAP (88 mg, 0.72 mmol), and Ac₂O (0.68 mL, 7.24 mmol) were

added. The resulting mixture was stirred at room temperature for 3 h and then diluted with

EtOAc. The mixture was thoroughly washed with water and brine, and the organic layer

was dried with anhydrous Na₂SO₄. After ﬁltration, the solution was concentrated under

vacuum to give a residue. The residue was dissolved in THF (120 mL), and anhydrous

pyridine (0.3 mL) was added dropwise. After the mixture was stirred for 40 min, a solution

of Pb(OAc)₄(1.5 mg, 3.2 mmol) in HOAc (51 mL) was added dropwise at

−

78 ^◦C. The

mixture was warmed to room temperature and then stirred for 24 h. The reaction mixture

◦

was cooled to 0 C, and a solution of NaBH₄(136 mg, 1.7 mmol) in NaOH (1M, 46 mL) was

slowly added. The resulting solution was stirred at 0 ^◦C for an additional 1 h and diluted

with EtOAc. The mixture was washed with a saturated NaHCO₃solution and then brine,

and the organic layer was dried with anhydrous Na₂SO₄. After ﬁltration, the solution

was concentrated to give a residue, which was puriﬁed by ﬂash column chromatography

on silica gel (petroleum/EtOAc = 7:1) to give compound 15 (1.4 g, 63% for 3 steps) as a

white foamy solid. R_f= 0.3 (silica, PE/EtOAc = 4:1); [α]²_D⁵= 98.9 (c = 1.0, CHCl₃); ¹H NMR

(

500 MHz, CDCl₃): δ 5.81 (d, J = 10.3 Hz, 1H), 5.44–5.36 (m, 2H), 4.17–4.07 (m, 2H), 3.95

(d, J = 7.5 Hz, 1H), 3.16 (d, J = 7.5 Hz, 1H), 2.80–2.75 (m, 1H), 2.57–2.50 (m, 1H), 2.13 (s,

3H), 2.02 (d, J = 3.1 Hz, 6H), 1.12 (s, 3H), 1.08 (s, 3H), 1.00 (s, 3H), 0.93 (s, 6H), 0.86 (s, 3H).

¹³C NMR (126 MHz, CDCl₃):

δ 170.88, 170.67, 170.06, 169.77, 131.93, 130.23, 83.63, 73.20,

68.54, 67.63, 51.72, 51.63, 47.88, 45.24, 45.19, 44.09, 41.60, 37.36, 37.01, 35.91, 34.17, 33.37,

31.85, 31.45, 30.44, 25.34, 23.69, 21.26, 21.01, 20.40, 20.06, 19.95, 19.02, 18.71, 18.56, 17.44.

ESI-HRMS (m/z) calcd for C₃₆H₅₃NNaO₇[M + Na]⁺634.3714, found 634.3717.

3.2.6. Synthesis of Compound 16

A solution of compound 15 (1.0 g, 1.6 mmol) and Na₂CO₃(866 mg, 8.2 mmol) in

MeOH (120 mL) was stirred at room temperature for 24 h. After removing MeOH in vacuo,

the resulting colorless solid was dissolved in Et₂O. The organic layer was washed with 1 N

HCl solution, saturated NaHCO₃solution and brine, dried over anhydrous Na₂SO₄, and

ﬁltered. The ﬁltrate was evaporated in vacuo to give a solid.

To a solution of the above product in THF (55 mL), NH₄OAc (1.5 g, 20 mmol) and

a buffered solution of TiCl₃(3.4 mL of HCl solution containing 15% TiCl₃, 4 mmol) were

added. The mixture was stirred at room temperature for 8 h. The mixture was washed

with saturated NaHCO₃solution and brine, dried over anhydrous Na₂SO₄, ﬁltered, and

evaporated in vacuo to give a solid. The solid was puriﬁed by silica gel ﬂash column

chromatography (petroleum ether/EtOAc = 2/1) to give compound 16 (613 mg, 80%) as

1

a white foam. R_f= 0.5 (silica, PE/EtOAc = 1:1); [α]²_D⁵= 89.4 (c = 1.0, CHCl₃); H NMR

(

500 MHz, CDCl₃): δ 5.91–5.81 (m, 1H), 5.47 (dd, J = 10.3, 3.1 Hz, 1H), 4.21 (dd, J = 10.1,

5.9 Hz, 1H), 3.92 (d, J = 7.4 Hz, 1H), 3.70 (d, J = 11.4 Hz, 1H), 3.40 (d, J = 11.4 Hz, 1H), 3.13

(d, J = 7.5 Hz, 1H), 2.68 (m, 1H), 2.31 (m, 1H), 2.11 (m, 1H), 1.14 (s, 3H), 1.11 (s, 3H), 1.01 (s,

3H), 1.00 (s. 3H), 0.99 (s, 3H), 0.91 (s, 3H). ¹³C NMR (125 MHz, CDCl₃):

δ 218.37, 131.71,

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130.37, 72.28, 66.39, 64.99, 52.75, 51.80, 51.52, 48.41, 46.21, 45.51, 41.70, 38.73, 37.33, 35.91,

35.29, 35.01, 34.17, 33.53, 31.46, 30.67, 29.69, 24.94, 23.67, 20.61, 19.36, 18.31, 17.28, 16.25.

ESI-HRMS (m/z) calcd for C₃₀H₄₆NaO₄[M + Na]⁺493.3288, found 493.3283.

3.2.7. Synthesis of Compound 17

To a stirred solution of compound 16 (90 mg, 0.2 mmol) in pyridine (4 mL), pivaloyl

chloride (0.5 mL, 4 mmol) and DMAP (6 mg, 0.06 mmol) were added. The mixture was

stirred at room temperature for 8 h before it was quenched with NaHCO₃and extracted

with EtOAc. The combined organic phases were washed with brine, dried over anhydrous

Na₂SO₄, ﬁltered, and concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography on silica gel (petroleum ether/EtOAc = 8/1) to give the acylated

product (115 mg, 94%) as a white solid. R_f= 0.5 (silica, PE/EtOAc = 3:1); [α]²_D⁵= 113.9

(

c = 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃):

δ 5.90 (d, J = 10.3 Hz, 1H), 5.48 (dd, J = 10.3,

3.1 Hz, 1H), 5.39 (m, 1H), 4.13–4.03 (m, 2H), 4.00 (d, J = 7.4 Hz, 1H), 3.22 (d, J = 7.1 Hz,

1H), 2.60 (m, 1H), 2.46 (m, 1H), 1.20 (s, 9H), 1.17 (s, 9H), 1.15 (s, 3H), 1.06 (s, 3H), 1.05 (s,

3H), 1.00 (s, 3H), 0.97 (s, 3H), 0.90 (s, 3H). ¹³C NMR (125 MHz, CDCl₃):

δ 213.52, 178.05,

177.81, 130.99, 83.74, 73.20, 68.03, 66.70, 51.75, 51.65, 50.54, 47.52, 45.34, 45.21, 41.61, 38.93,

38.77, 37.66, 37.33, 35.65, 34.58, 34.03, 33.31, 31.57, 31.39, 30.47, 27.20, 25.20, 23.65, 20.27,

19.18, 18.56, 16.97, 16.56. ESI-HRMS (m/z) calcd for C₄₀H₆₂NaO₆[M + Na]⁺661.4439,

found 661.4445.

◦

To a stirred solution of the above product (90 mg, 0.14 mmol) in MeOH (3 mL) at 0 C,

NaBH₄(23 mg, 0.5 mmol) was added. The stirring continued for 15 min, the solution was

quenched by addition of saturated NH₄Cl solution, then diluted with brine and extracted

with CH₂Cl₂. The extract was dried over anhydrous Na₂SO₄, ﬁltered, and concentrated

in vacuo. The residue was puriﬁed by silica gel column chromatography (petroleum

ether/EtOAc = 4/1) to give compound 17 (76 mg, 85%) as a white foam. R_f= 0.3 (silica,

1

PE/EtOAc = 3:1); [α]²_D⁵= 65.3 (c = 1.0, CHCl₃); H NMR (500 MHz, CDCl₃):

δ 5.88 (d,

J = 10.3 Hz, 1H), 5.42 (dd, J = 10.2, 3.0 Hz, 1H), 5.40–5.35 (m, 1H), 4.19 (d, J = 11.6 Hz, 1H),

3.99 (d, J = 7.4 Hz, 1H), 3.75 (d, J = 11.5 Hz, 1H), 3.36 (t, J = 8.2 Hz, 1H), 3.21 (d, J = 7.4 Hz

1H), 2.33 (t, J = 7.5 Hz, 1H), 1.21 (s, 9H), 1.20 (s, 9H), 1.09 (s, 3H), 1.03 (s, 3H), 0.96 (s, 3H),

0.93 (s, 3H), 0.88 (s, 3H), 0.75 (s, 3H). ¹³C NMR (125 MHz, CDCl₃):

178.76, 178.14, 132.52,

,

δ

129.64, 83.88, 73.14, 72.26, 68.19, 65.77, 52.75, 51.62, 47.73, 45.31, 45.17, 42.42, 41.68, 38.32,

37.32, 36.08, 34.05, 33.32, 31.56, 31.38, 31.05, 29.68, 27.31, 27.19, 25.91, 25.21, 23.64, 20.44,

19.43, 18.16, 17.37, 11.39. ESI-HRMS (m/z) calcd for C₄₀H₆₄NaO₆[M + Na]⁺663.4595,

found 663.4598.

3.2.8. Synthesis of Compound 18

To a stirred mixture of compound 11 (180 mg, 0.24 mmol), compound 17 (120 mg,

0.18 mmol), and 4Å molecular sieves (400 mg) in CH₂Cl₂(4 mL), PPh₃AuNTf₂(26 mg,

0.04 mmol) was added. The mixture was stirred at room temperature for 1 h before it was

quenched with NEt₃. The mixture was ﬁltered through a pad of celite and washed with

EtOAc. The ﬁltrate was concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography (petroleum ether/EtOAc = 4:1) to give compound 18 (190 mg,

84%) as a white foam. R_f= 0.3 (silica, PE/EtOAc = 3:1); [α]²_D⁵= 43.9 (c = 1.0, CHCl₃); ¹H

NMR (600 MHz, CDCl₃):

δ 5.91–5.78 (m, 1H), 5.47–5.38 (m, 1H), 5.36 (dd, J = 9.6, 6.2 Hz,

1H), 5.18 (d, J = 3.5 Hz, 1H), 5.10 (m, 3H), 4.87 (t, J = 8.5 Hz, 1H), 4.58 (d, J = 7.9 Hz, 1H), 4.26

(m, 2H), 4.13 (m, 1H), 3.97 (d, J = 7.4 Hz, 1H), 3.81 (d, J = 11.3 Hz, 1H), 3.77–3.71 (m, 2H),

3.66–3.62 (m, 1H), 3.61 (d, J = 6.5 Hz, 1H), 3.36 (dd, J = 11.5, 4.7 Hz, 1H), 3.19 (d, J = 7.4 Hz

,

1H), 2.11 (s, 3H), 2.10 (s, 3H), 2.09 (s, 3H), 2.00 (s, 3H), 1.99 (s, 3H), 1.97 (s, 3H), 1.24 (s, 9H),

1.19 (s, 9H), 1.17 (s, 3H), 1.07 (s, 3H), 1.00 (s, 3H), 0.95 (s, 3H), 0.90 (s, 3H), 0.88 (s, 3H), 0.71

(s, 3H). ¹³C NMR (150 MHz, CDCl₃):

δ 102.85, 100.52, 73.15, 72.60, 71.75, 71.68, 71.26, 71.10,

69.30, 68.31, 68.19, 65.00, 61.31, 52.72, 51.62, 47.66, 45.32, 45.17, 42.04, 41.69, 39.06, 38.96,

38.11, 37.35, 35.79, 34.08, 33.36, 31.55, 31.41, 30.98, 27.38, 27.32, 27.20, 25.28, 25.23, 23.65,

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20.98, 20.76, 20.59, 20.40, 20.37, 19.44, 17.94, 17.22, 16.35, 12.17. ESI-HRMS (m/z) calcd for

C₆₄H₉₆NaO₂₁[M + Na]⁺1223.6336, found 1223.6318.

3.2.9. Synthesis of Saikosaponin A (1)

To a stirred solution of compound 18 (110 mg, 0.1 mmol) in MeOH (3 mL), KOH

(

261 mg, 4.6 mmol) was added at room temperature. The mixture was stirred at reﬂux

for 24 h before it was quenched with acetic acid. The mixture was concentrated under

vacuum. The residue was puriﬁed by reversed-phase silica gel column chromatography

(ODS RP-18) (MeOH/H₂O = 5:1 to 7:1) to give saikosaponin A (

powder. Rf = 0.4 (silica, CHCl₃/MeOH = 5:1); [α]²_D⁵5.9 (c = 1.0, CH₃OH); ¹H NMR

600 MHz, pyridine-d₅): 6.07–5.99 (m, 1H), 5.73–5.63 (m, 1H), 5.35 (d, J = 7.8 Hz, 1H), 5.00

1) (69 mg, 93%) as a white

=

−

(

δ

(d, J = 7.8 Hz, 1H), 4.57 (m, 4H), 4.45–4.37 (m, 4H), 4.30 (m, 2H), 4.23 (m, 1H), 4.09–4.01

(m, 3H), 3.75–3.67 (m, 2H), 3.36 (d, J = 6.9 Hz, 1H), 2.52 (m, 1H), 2.35 (m, 1H), 1.45 (d,

J = 6.3 Hz, 3H), 1.41 (s, 3H), 1.12 (s, 3H), 1.01 (s, 3H), 0.95 (s, 3H), 0.94 (s, 3H), 0.91 (s, 3H).

¹³C NMR (150 MHz, Pyridine-d₅):

δ 132.14, 131.11, 106.58, 105.95, 85.12, 83.94, 81.53, 78.71,

78.36, 75.76, 72.97, 72.09, 71.77, 71.49, 70.96, 64.00, 63.92, 62.64, 53.03, 52.09, 47.23, 46.94,

45.58, 43.68, 42.14, 38.60, 37.67, 36.20, 36.06, 34.62, 33.59, 31.55, 31.52, 26.06, 25.70, 23.77,

20.79, 19.99, 18.69, 17.49, 17.22, 13.00. ESI-HRMS (m/z) calcd for C₄₂H₆₈NaO₁₃[M + Na]⁺

803.4552, found 803.4549.

3.2.10. Synthesis of Compound 19

Compound 16 (290 mg, 0.6 mmol) was dissolved in CH₂Cl₂(10 mL), to which DMP

(636 mg, 1.5 mmol) was added. After being stirred for 40 min at room temperature, the

reaction mixture was quenched with a saturated Na₂S₂O₃solution and the aqueous phase

was extracted with CH₂Cl₂. The combined organic extracts were dried over anhydrous

Na₂SO₄and concentrated in vacuo.

To a solution of the above product in MeOH (10 mL) under stirring at 0 ^◦C, NaBH₄

(95 mg, 2.5 mmol) was added. The mixture was stirred for 15 min before it was quenched

by addition of saturated NH₄Cl solution. The mixture was diluted with brine and extracted

with CH₂Cl₂. The combined organic phases were dried over anhydrous Na₂SO₄, ﬁltered,

and concentrated in vacuo. The residue was puriﬁed by silica gel column chromatography

(petroleum ether/EtOAc = 2/1) to give compound 19 (190 mg, 65%) as a white foam.

1

R_f= 0.3 (silica, PE/EtOAc = 2:1); [α]²_D⁵= 11.2 (c = 1.0, Pyridine); H NMR (500 MHz,

Pyridine-d₅):

J = 5.6 Hz, 1H), 3.36 (d, J = 5.4 Hz, 1H), 2.69 (m, 1H), 2.52 (m, 1H), 1.64 (s, 3H), 1.41 (s, 3H),

1.10 (s, 6H), 1.06 (s, 3H), 1.00 (s, 3H). ¹³C NMR (125 MHz, Pyridine-d₅):

132.46, 132.39,

δ 6.05 (m, 1H), 5.74 (d, J = 8.8 Hz, 1H), 3.74 (d, J = 9.8 Hz, 1H), 3.62 (d,

δ

85.30, 78.25, 77.58, 73.76, 68.15, 53.43, 51.80, 48.87, 45.79, 44.05, 43.50, 42.31, 39.10, 38.87,

37.25, 37.02, 35.88, 34.21, 32.34, 32.03, 31.74, 28.03, 24.89, 19.99, 19.14, 18.55, 18.44, 12.98.

ESI-HRMS (m/z) calcd for C₃₀H₄₈NaO₄[M + Na]⁺495.3445, found 495.3437.

3.2.11. Synthesis of Compound 20

To a stirred solution of compound 19 (187 mg, 0.4 mmol) in CH₂Cl₂(4 mL), pivaloyl

chloride (58

was stirred at

µ

L, 0.48 mmol) and pyridine (0.57 mL, 7.2 mmol) were added. The mixture

−

10 ^◦C for 8 h before it was quenched with NaHCO₃and extracted with

EtOAc. The combined organic phases were washed with brine, dried over anhydrous

Na₂SO₄, ﬁltered, and concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography on silica gel (petroleum ether/EtOAc = 8/1) to give compound

20 (178 mg, 81%) as a white solid. R_f= 0.3 (silica, PE/EtOAc = 3:1); [α]²_D⁵= 41.7 (c = 1.0,

CHCl₃); ¹H NMR (500 MHz,CDCl₃):

δ 5.87 (d, J = 10.4 Hz, 1H), 5.42 (dd, J = 10.3, 3.0 Hz,

1H), 4.17 (d, J = 11.5 Hz, 1H), 4.00 (d, J = 4.9 Hz, 1H), 3.78 (d, J = 11.5 Hz, 1H), 3.45 (d,

J = 7.3 Hz, 1H), 3.40–3.36 (m, 1H), 3.17 (d, J = 7.3 Hz, 1H), 2.20 (m, 1H), 1.25 (s, 3H), 1.21 (s,

9H), 1.05 (s, 3H), 0.95 (s, 3H), 0.93 (s, 3H), 0.91 (s, 3H), 0.75 (s, 3H). ¹³C NMR (125 MHz,

CDCl₃):

δ 178.84, 132.14, 130.83, 84.74, 78.12, 72.49, 66.10, 52.88, 50.47, 47.92, 45.00, 42.98,

42.57, 41.46, 39.16, 38.41, 38.13, 36.79, 36.25, 35.10, 33.55, 31.72, 31.17, 30.47, 29.82, 27.47,

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27.19, 26.13, 24.26, 19.11, 18.36, 18.00, 17.61, 11.52. ESI-HRMS (m/z) calcd for C₃₅H₅₆NaO₅

[M + Na]⁺579.4020, found 579.4016.

3.2.12. Synthesis of Compound 21

A solution of tetramethylammonium triacetoxyborohydride (1.9 g, 7.2 mmol) in MeCN

(27 mL) and AcOH (1.12 mL) was cooled to

−

40 ^◦C. To the mixture was added a solution

of the compound 16 (680 mg, 1.4 mmol) in CH₂Cl₂(9 mL). The mixture was stirred at room

temperature for 0.5 h before it was quenched with Rochelle salt (sat. aq.) and extracted

with EtOAc. The combined organic phases were washed with brine, dried over anhydrous

Na₂SO₄, ﬁltered, and concentrated under vacuum.

The above product was dissolved into DMF (5 mL), to which 2,6-lutidine (2.5 mL) was

◦

added, and the solution was cooled to 0 C. Di-tert-butylsilylbis(triﬂuoromethansulfonate)

(0. 6 mL, 1.7 mmol) was added. The mixture was stirred at room temperature for 2 h

before it was quenched with NaHCO₃and extracted with EtOAc. The combined organic

phases were washed with brine, dried over anhydrous Na₂SO₄, ﬁltered, and concentrated

under vacuum.

The above product was dissolved in CH₂Cl₂(5 mL), then the solution was added

DMP (736 mg, 1.7 mmol). After being stirred for 40 min at room temperature, the reaction

mixture was quenched with a saturated Na₂S₂O₃solution, and the aqueous phase was

extracted with CH₂Cl₂. The combined organic extracts were dried over anhydrous Na₂SO₄

and concentrated in vacuo. The residue was puriﬁed by ﬂash chromatography (petroleum

ether/EtOAc = 15:1) to give compound 21 (507 mg, 74%) as a white solid. R_f= 0.5 (silica,

1

PE/EtOAc = 6:1); [α]²_D⁵= 12.9 (c = 1.0, CHCl₃); H NMR (500 MHz, CDCl₃):

δ 5.95 (d,

J = 10.3 Hz, 1H), 5.56–5.52 (m, 1H), 3.86 (m, 3H), 3.72 (d, J = 10.3 Hz, 1H), 3.44 (d, J = 7.9 Hz

,

1H), 2.68 (m, 1H), 2.23 (m, 1H), 2.15 (m, 1H), 1.09 (s, 9H), 1.07 (s, 3H), 1.05 (s, 3H), 1.03

(s, 9H), 0.98 (s, 3H), 0.95 (s, 3H), 0.92 (s, 3H), 0.86 (s, 3H). ¹³C NMR (125 MHz, CDCl₃):

δ

213.14, 213.12, 133.20, 128.84, 84.15, 80.53, 75.56, 56.35, 55.03, 52.37, 52.28, 49.63, 44.49,

41.78, 41.04, 38.89, 38.79, 36.64, 35.54, 33.40, 31.68, 31.09, 29.24, 27.94, 27.83, 26.68, 24.31,

23.70, 23.29, 20.50, 20.23, 19.52, 18.75, 17.14, 12.28. ESI-HRMS (m/z) calcd for C₃₈H₆₃O₄Si

[M + H]⁺611.4490, found 611.4488.

3.2.13. Synthesis of Compound 22

The compound 21 was dissolved in THF (5 mL), to which HF pyr (1 mL) was

·

added at room temperature. After stirring at room temperature for 1 h, the mixture

was quenched with saturated NaHCO₃and extracted with EtOAc. The combined organic

phases were washed with brine, dried over anhydrous Na₂SO₄, ﬁltered, and concentrated

under vacuum. The residue was puriﬁed by ﬂash column chromatography (petroleum

ether/EtOAc = 2:1) to give the diol product (500 mg, 99%) as a white foam. R_f= 0.3 (silica,

PE/EtOAc = 3:1); [α]²_D⁵= 12.9 (c = 1.0, Pyridine); ¹H NMR (500 MHz, Pyridine-d₅):

δ 6.11

(d, J = 10.4 Hz, 1H), 5.74 (m, 1H), 4.26 (dd, J = 11.2, 5.3 Hz, 1H), 4.22 (d, J = 10.4 Hz, 1H),

3.96 (d, J = 7.8 Hz, 1H), 3.74 (d, J = 10.4 Hz, 1H), 3.54 (d, J = 7.8 Hz, 1H), 2.87 (m, 1H), 2.36

(m, 1H), 1.42 (s, 3H), 1.07 (s, 3H), 1.05 (s, 3H), 1.03 (s, 3H), 0.87 (s, 3H), 0.83 (s, 3H). ¹³

C

NMR (125 MHz, pyridine-d₅):

δ 212.80, 133.74, 129.94, 84.73, 75.90, 73.18, 67.47, 56.85, 55.59,

53.25, 50.29, 48.50, 45.25, 43.62, 42.56, 39.47, 39.02, 36.97, 36.36, 33.78, 32.12, 31.86, 28.05,

24.97, 23.60, 20.70, 20.28, 18.98, 18.28, 13.08. ESI-HRMS (m/z) calcd for C₃₀H₄₇O₄[M + H]⁺

471.3469, found 471.3463.

To a stirred solution of the above product (470 mg, 1 mmol) in CH₂Cl₂(10 mL),

pivaloyl chloride (0.15 mL_◦, 1.2 mmol) and pyridine (0.8 mL, 12 mmol) were added. The

mixture was stirred at

−

10 C for 30 h before it was quenched with NaHCO₃and extracted

with EtOAc. The combined organic phases were washed with brine, dried over anhydrous

Na₂SO₄, ﬁltered, and concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography on silica gel (petroleum ether/EtOAc = 9/1) to give compound 22

(487 mg, 81%) as a white solid. R_f= 0.4 (silica, PE/EtOAc = 3:1); [α]²_D⁵= 12.9 (c = 1.0, CHCl₃);

¹H NMR (500 MHz, CDCl₃):

δ 5.94 (d, J = 10.3 Hz, 1H), 5.52 (dd, J = 10.3, 2.8 Hz, 1H), 4.15

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(d, J = 11.5 Hz, 1H), 3.85 (d, J = 8.0 Hz, 1H), 3.75 (d, J = 11.5 Hz, 1H), 3.41 (t, J = 11.6 Hz

,

1H), 3.37–3.28 (m, 1H), 2.75–2.56 (m, 1H), 1.18 (s, 9H), 1.16 (s, 3H), 0.95 (s, 3H), 0.92 (s, 3H),

0.88 (s, 3H), 0.83 (s, 3H), 0.73 (s, 3H). ¹³C NMR (125 MHz, CDCl₃):

δ 213.04, 178.70, 133.13,

128.79, 84.14, 75.50, 72.23, 65.91, 56.26, 54.97, 52.70, 49.55, 47.87, 44.39, 42.47, 41.69, 39.09,

38.85, 38.35, 36.17, 35.47, 33.33, 31.57, 31.08, 27.37, 26.00, 24.21, 23.21, 20.11, 19.46, 18.16,

17.44, 11.50. ESI-HRMS (m/z) calcd for C₃₅H₅₄NaO₅[M + Na]⁺577.3863, found 577.3868.

3.2.14. Synthesis of Compound 23

To a stirred mixture of compound 22 (50 mg, 0.09 mmol), compound 12 (102 mg,

0.11 mmol), and 4Å molecular sieves (200 mg) in CH₂Cl₂(2 mL), PPh₃AuNTf₂(13 mg,

0.02 mmol) was added. The mixture was stirred at room temperature for 1 h before it was

quenched with NEt₃. The mixture was ﬁltered through a pad of celite and washed with

EtOAc. The ﬁltrate was concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography (petroleum ether/EtOAc = 3:1) to give compound 23 (107 mg,

95%) as a white foam. R_f= 0.3 (silica, PE/EtOAc = 4:1); [α]²_D⁵= 53.3 (c = 1.0, CHCl₃); ¹H

NMR (500 MHz, CDCl₃):

δ 8.09 (d, J = 7.3 Hz, 4H), 7.60–7.56 (m, 2H), 7.47 (t, J = 6.7 Hz,

4H), 5.93 (d, J = 10.4 Hz, 1H), 5.60–5.45 (m, 3H), 5.04–4.86 (m, 3H), 4.75 (m, 2H), 4.61 (d,

J = 7.8 Hz, 1H), 4.50 (d, J = 7.9 Hz, 1H), 4.19 (d, J = 10.1 Hz, 2H), 4.14–4.09 (m, 2H), 4.04

(m, 1H), 3.85 (d, J = 7.8 Hz, 1H), 3.77 (t, J = 9.7 Hz, 2H), 3.59 (d, J = 9.2 Hz, 1H), 3.51 (d,

J = 11.6 Hz, 1H), 3.45–3.37 (m, 2H), 2.66 (m, 1H), 2.22 (m, 1H), 2.13 (m, 1H), 1.98 (s, 3H),

1.94 (s, 3H), 1.83 (s, 3H), 1.44 (s, 3H), 1.25 (d, J = 6.0 Hz, 3H), 1.21 (s, 9H), 1.12 (s, 3H), 0.93

(s, 3H), 0.89 (s, 3H), 0.88 (s, 3H), 0.85 (s, 3H), 0.50 (s, 3H). ¹³C NMR (125 MHz, CDCl₃):

δ

213.11, 177.70, 170.94, 170.33, 169.31, 168.99, 166.38, 165.05, 133.54, 133.21, 133.15, 130.27,

129.97, 129.56, 128.74, 128.46, 102.87, 101.00, 84.16, 81.63, 78.02, 75.55, 72.82, 71.74, 71.66,

71.08, 69.97, 68.10, 64.75, 61.43, 56.30, 55.01, 52.71, 49.60, 47.70, 44.42, 42.22, 41.70, 39.15,

38.89, 38.26, 35.86, 35.52, 33.38, 31.63, 31.00, 27.49, 27.43, 25.46, 24.27, 23.24, 20.78, 20.66,

20.59, 20.08, 19.78, 19.47, 17.86, 17.21, 16.89, 12.01. ESI-HRMS (m/z) calcd for C₆₉H₉₀NaO₂₀

[M + Na]⁺1261.5918, found 1261.5925.

3.2.15. Synthesis of Saikosaponin D (2)

◦

To a solution of compound 23 (102 mg, 0.08 mmol) in i-PrOH (2 mL) at

−

20 C, NaBH₄

(15 mg, 0.4 mmol) was added. The mixture was stirred for 3 h before it was quenched by

addition of saturated NH₄Cl solution and diluted with brine and extracted with CH₂Cl₂.

The extract was dried over anhydrous Na₂SO₄, ﬁltered, and concentrated in vacuo. The

residue was puriﬁed by silica gel column chromatography (petroleum ether/EtOAc = 6/1)

to give the 16-OH product (90 mg, 89%) as a white foam.

To a solution of the above product (49 mg, 0.04 mmol) in MeOH (3 mL), KOH (110 mg

,

2 mmol) was added at room temperature. The mixture was stirred at 55 ^◦C for 24 h before

it was quenched with acetic acid. The mixture was concentrated under vacuum. The

residue was puriﬁed by reversed-phase silica gel column chromatography (ODS RP-18)

(CHCl₃/MeOH = 5:1 to 7:1) to give saikosaponin D (

R_f= 0.6 (silica, CHCl₃/MeOH = 3:1); [α]²_D⁵= 40.4 (c = 1.0, CH₃OH); ¹H NMR (500 MHz,

pyridine-d₅): 6.31 (d, J = 4.1 Hz, 1H), 6.06 (d, J = 10.3 Hz, 1H), 5.73 (d, J = 2.8 Hz, 1H), 5.71

2) (26 mg, 83%) as a white powder.

δ

(d, J = 2.6 Hz, 1H), 5.36 (d, J = 7.8 Hz, 1H), 5.00 (d, J = 7.8 Hz, 1H), 4.57 (m, 2H), 4.46–4.37

(m, 2H), 4.28 (m, 5H), 4.09–4.02 (m, 3H), 3.73 (d, J = 10.8 Hz, 1H), 3.71–3.67 (m, 1H), 3.62 (d,

J = 3.2 Hz, 1H), 3.60 (d, J = 7.0 Hz, 1H), 3.35 (d, J = 7.0 Hz, 1H), 2.74–2.64 (m, 1H), 1.65 (s,

3H), 1.46 (s, 3H), 1.45 (s, 3H), 1.38 (s, 3H), 1.04 (s, 3H), 0.98 (s, 3H), 0.96 (s,3H). ¹³C NMR

(126 MHz, pyridine-d₅):

δ 150.59, 150.46, 150.25, 150.03, 136.22, 136.13, 135.93, 135.73, 132.41,

132.35, 124.20, 124.10, 123.90, 123.70, 107.09, 106.40, 85.63, 85.28, 82.03, 79.20, 78.83, 78.20,

77.52, 76.22, 72.55, 72.22, 71.93, 71.42, 64.43, 63.08, 53.42, 51.74, 50.07, 47.75, 45.73, 44.14,

43.99, 42.27, 39.05, 38.76, 37.21, 36.68, 35.85, 34.15, 32.29, 31.93, 31.69, 26.53, 24.80, 19.95,

19.24, 18.50, 17.96, 17.65, 13. ESI-HRMS (m/z) calcd for C₄₂H₆₉NaO₁₃[M + H]⁺781.4733,

found 781.4736.

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3.2.16. Synthesis of Saikosaponin Y (5)

To a stirred solution of the compound 23 (85 mg, 0.07 mmol) in MeOH (3 mL), KOH

(307 mg, 5.5 mmol) was added at room temperature. The mixture was stirred at 55 ^◦C for

24 h before it was quenched with acetic acid. The mixture was concentrated under vacuum.

The residue was puriﬁed by reversed-phase silica gel column chromatography (ODS RP-18)

(CHCl₃/MeOH = 5:1 to 7:1) to give saikosaponin Y (

Rf = 0.3 (silica, CHCl₃/MeOH = 4:1); [α]²_D⁵= 26.6 (c = 1.0, CH₃OH); ¹H NMR (500 MHz

CD₃OD): 6.02 (d, J = 10.3 Hz, 1H), 5.52 (dd, J = 10.2, 3.1 Hz, 1H), 4.53 (d, J = 7.7 Hz, 1H),

5) (50 mg, 94%) as a white powder.

,

δ

4.37 (d, J = 7.4 Hz, 1H), 3.89(d, J = 7.4 Hz, 1H), 3.97–3.71 (m, 2H), 3.76–3.53 (m, 7H), 3.43 (d,

J = 7.9 Hz, 1H), 3.40–3.15 (m, 7H), 2.77 (m, 1H), 2.26 (m, 1H), 2.09 (m, 1H), 1.25 (d, J = 6.2 Hz,

3H), 1.19 (s, 3H), 1.00 (s, 3H), 0.96 (s, 3H), 0.91 (s, 3H), 0.89 (s, 3H), 0.70 (s, 3H). ¹³C NMR

(125 MHz, CD₃OD): δ 214.74, 134.56, 129.61, 105.65, 85.59, 85.12, 82.97, 77.88, 77.66, 76.29,

75.33, 72.33, 71.82, 71.32, 71.18, 62.35, 57.35, 56.24, 53.73, 50.84, 47.97, 45.39, 44.05, 42.98,

39.98, 39.18, 37.07, 36.64, 33.84, 32.45, 32.03, 26.14, 25.08, 23.52, 20.75, 20.16, 18.88, 18.12,

16.98, 12.80. ESI-HRMS (m/z) calcd for C₄₂H₆₇O₁₃[M + H]⁺779.4576, found 779.4569.

3.2.17. Synthesis of Compound 24

To a stirred solution of compound 9 (290 mg, 1.1 mmol) in pyridine (5 mL), benzoyl

chloride (0.8 mL, 4.9 mmol) and DMAP (39 mg, 0.3 mmol) were added. The mixture was

stirred at room temperature for 8 h before it was quenched with NaHCO₃and extracted

with EtOAc. The combined organic phases were washed with brine, dried over anhydrous

Na₂SO₄, ﬁltered, and concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography on silica gel (petroleum ether/EtOAc = 9/1) to give corresponding

benzoylated product (625 mg, 99%) as a white solid.

To a stirred solution of the above product (582 mg, 1.0 mmol) in CH₃CN/H₂O

(

8 mL/2 mL), ceric ammonium nitrate (1.2 g, 2.1 mmol) was added. The mixture was

stirred at room temperature for 2 h before it was quenched with Na₂S₂O₃and extracted

with EtOAc. The combined organic phases were washed with brine, dried over anhydrous

Na₂SO₄, ﬁltered, and concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography (petroleum ether/EtOAc = 2:1) to give the lactol (375 mg, 81%) as

an orange foam. The α/β anomers were difﬁcult to separate.

The lactol (298 mg, 0.62 mmol), ortho-(cyclopropylethynyl) benzoic acid (138 mg,

0.82 mmol), EDCI (156 mg, 0.82 mmol), and DMAP (100 mg, 0.82 mmol) were dissolved in

CH₂Cl₂(5 mL). The mixture was stirred at room temperature for 4 h and concentrated under

vacuum. The residue was puriﬁed by ﬂash chromatography (petroleum ether/EtOAc = 3:1

)

to give compound 24 (401 mg, 99%; α/β = 1:2.1) as a white foam.

1

24α: R_f= 0.3 (silica, PE/EtOAc = 4:1); [α]²_D⁵= 205.6 (c = 1.0, CHCl₃); H NMR

(500 MHz,CDCl₃): δ 8.14 (d, J = 7.3 Hz, 2H), 8.01 (d, J = 7.6 Hz, 1H), 7.89 (d, J = 7.4 Hz, 2H),

7.82 (d, J = 7.4 Hz, 2H), 7.64 (t, J = 7.4 Hz, 1H), 7.50 (m, 6H), 7.37 (t, J = 7.2 Hz, 1H), 7.28

(m, 4H), 6.94 (d, J = 3.6 Hz, 1H), 6.12 (dd, J = 10.7, 3.3 Hz, 1H), 6.02 (dd, J = 10.7, 3.6 Hz,

1H), 5.93 (d, J = 2.7 Hz, 1H), 4.82 (q, J = 6.4 Hz, 1H), 1.60 (m, 1H), 1.35 (d, J = 6.5 Hz, 3H),

0.95–0.82 (m, 4H). ¹³C NMR (125 MHz, CDCl₃):

δ 166.05, 165.76, 164.52, 135.08, 133.67,

133.44, 133.34, 132.41, 130.98, 130.54, 130.03, 129.88, 129.77, 129.26, 129.11, 128.95, 128.76,

128.46, 128.40, 127.41, 125.06, 99.97, 91.16, 74.95, 71.56, 69.31, 68.30, 67.70, 16.38, 9.13, 9.10.

24β: R_f= 0.25 (silica, PE/EtOAc = 4:1); [α]²_D⁵= 216.5 (c = 1.0, CHCl₃); H NMR

500 MHz, CDCl₃): δ 8.16–8.12 (m, 2H), 8.01–7.98 (m, 1H), 7.92–7.88 (m, 2H), 7.81 (dd,

1

(

J = 8.2, 7.1 Hz, 2H), 7.63 (t, J = 7.4 Hz, 1H), 7.50 (t, J = 7.7 Hz, 2H), 7.47–7.38 (m, 4H), 7.32 (t,

J = 7.8 Hz, 2H), 7.29–7.24 (m, 3H), 6.26 (d, J = 8.4 Hz, 1H), 6.03 (dd, J = 10.3, 8.4 Hz, 1H),

5.81 (d, J = 3.0 Hz, 1H), 5.70 (dd, J = 10.4, 3.5 Hz, 1H), 4.33 (q, J = 6.2 Hz, 1H), 1.54 (m,

1H), 1.39 (d, J = 6.4 Hz, 3H), 0.90 (m, 4H). ¹³C NMR (125 MHz, CDCl₃):

δ 166.07, 165.69,

165.51, 163.75, 134.49, 133.65, 133.48, 133.42, 132.53, 131.08, 130.15, 129.89, 129.85, 129.50,

129.29, 129.04, 128.92, 128.72, 128.51, 128.43, 127.20, 125.84, 100.53, 92.90, 74.44, 72.22, 71.14,

71.01, 68.89, 16.33, 9.15, 9.11. ESI-HRMS (m/z) calcd for C₃₉H₃₂NaO₉[M + Na]⁺667.1339,

found 667.1934.

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3.2.18. Synthesis of Compound 25

To a stirred mixture of compound 24 (108 mg, 0.17 mmol), compound 17 (90mg,

0.14 mmol), and 4Å molecular sieves (300 mg) in CH₂Cl₂(3 mL), PPh₃AuNTf₂(21 mg,

0.03 mmol) was added. The mixture was stirred at room temperature for 1 h before it was

quenched with NEt₃. The mixture was ﬁltered through a pad of celite and washed with

EtOAc. The ﬁltrate was concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography (petroleum ether/EtOAc = 3:1) to give compound 25 (140 mg,

91%) as a white foam. R_f= 0.3 (silica, PE/EtOAc = 4:1); [α]²_D⁵= 216.5 (c = 1.0, CHCl₃);

¹H NMR (500 MHz, CDCl₃):

δ 8.10 (d, J = 7.5 Hz, 2H), 7.97 (d, J = 7.5 Hz, 2H), 7.76 (d,

J = 7.6 Hz, 2H), 7.60 (t, J = 7.4 Hz, 1H), 7.49 (m, 3H), 7.43–7.34 (m, 3H), 7.22 (t, J = 7.7 Hz,

2H), 5.89 (d, J = 10.4 Hz, 1H), 5.76 (dd, J = 10.2, 8.2 Hz, 1H), 5.70 (d, J = 3.0 Hz, 1H), 5.48

(dd, J = 10.5, 3.4 Hz, 1H), 5.42 (dd, J = 10.2, 2.2 Hz, 1H), 5.36 (dd, J = 9.2, 6.1 Hz, 1H), 4.69

(d, J = 7.9 Hz, 1H), 4.04–3.92 (m, 2H), 3.72 (d, J = 10.3 Hz, 1H), 3.65 (d, J = 11.6 Hz, 1H),

3.54 (dd, J = 11.6, 4.6 Hz, 1H), 3.20 (d, J = 7.2 Hz, 1H), 1.33 (d, J = 6.2 Hz, 3H), 1.24 (s, 9H),

1.19 (s, 9H), 1.05 (s, 3H), 1.00 (s, 3H), 0.96 (s, 3H), 0.90 (s, 3H), 0.88 (s, 3H), 0.57 (s, 3H).

¹³C NMR (125 MHz, CDCl₃):

δ 178.27, 177.40, 166.23, 165.83, 165.44, 133.51, 133.39, 133.29,

132.67, 130.17, 129.95, 129.85, 129.71, 129.37, 129.18, 128.97, 128.62, 128.54, 128.36, 103.35,

83.95, 82.76, 73.26, 72.31, 71.17, 69.92, 69.65, 68.27, 64.49, 52.81, 51.70, 47.54, 45.42, 45.26,

42.25, 41.77, 39.12, 39.06, 38.28, 37.42, 35.91, 34.17, 33.48, 31.64, 31.53, 31.04, 29.83, 27.54,

27.32, 25.47, 25.34, 23.78, 20.50, 19.58, 18.08, 17.19, 16.59, 12.07. ESI-HRMS (m/z) calcd for

C₆₇H₈₆NaO₁₃[M + Na]⁺1121.5961 found, 1121.5967.

3.2.19. Synthesis of Compound Prosaikogenin F (3)

To a stirred solution of compound 25 (105 mg, 0.1 mmol) in MeOH (3 mL), KOH

(

272 mg, 5.0 mmol) was added. The mixture was stirred at 55 ^◦C for 24 h before it was

quenched with acetic acid. The mixture was concentrated under vacuum. The residue was

puriﬁed by reversed-phase silica gel column chromatography (ODS RP-18) (CHCl₃/MeOH

= 5:1 to 7:1) to give prosaikogenin F (

3) (51 mg, 87%) as a white powder. R_f= 0.6 (silica,

CHCl₃/MeOH = 4:1); [α]²_D⁵= 78.6 (c = 1.0, CH₃OH); ¹H NMR (500 MHz, pyridine-d5):

δ

6.03 (d, J = 10.4 Hz, 1H), 5.69 (dd, J = 10.3, 2.9 Hz, 1H), 4.98 (d, J = 7.7 Hz, 1H), 4.56–4.50 (m,

1H), 4.44–4.35 (m, 3H), 4.31 (dd, J = 11.9, 4.5 Hz, 1H), 4.02 (d, J = 6.3 Hz, 2H), 3.82–3.75 (m,

1H), 3.71 (d, J = 10.7 Hz, 1H), 3.36 (d, J = 6.9 Hz, 1H), 2.51 (d, J = 13.3 Hz, 1H), 2.38 (m, 1H),

1.55 (d, J = 6.4 Hz, 3H), 1.42 (s, 3H), 1.12 (s, 3H), 1.02 (s, 3H), 0.95 (s, 3H), 0.94 (s, 3H), 0.92

(s, 3H). ¹³C NMR (125 MHz, pyridine-d₅):

δ 132.68, 131.67, 106.83, 84.48, 82.12, 75.99, 73.52,

73.46, 73.32, 71.77, 64.75, 64.54, 53.59, 52.65, 47.88, 47.50, 46.14, 44.19, 42.71, 39.15, 38.23,

36.81, 36.63, 35.19, 34.15, 32.11, 26.51, 26.26, 24.33, 21.36, 20.57, 19.29, 18.08, 18.00, 13.53.

ESI-HRMS (m/z) calcd for C₆₇H₈₆NaO₁₃[M + Na]⁺641.4024, found 641.4021.

3.2.20. Synthesis of Compound 26

To a stirred mixture of compound 24 (97 mg, 0.15 mmol), compound 22 (70 mg,

0.13 mmol), and 4Å molecular sieves (300 mg) in CH₂Cl₂(3 mL), PPh₃AuNTf₂(19 mg,

0.03 mmol) was added. The mixture was stirred at room temperature for 1 h before it was

quenched with NEt₃.The mixture was ﬁltered through a pad of celite and washed with

EtOAc. The ﬁltrate was concentrated under vacuum. The residue was puriﬁed by ﬂash

column chromatography (petroleum ether/EtOAc = 5:1) to give compound 26 (106 mg,

84%) as a white foam. R_f= 0.3 (silica, PE/EtOAc = 4:1); [α]²_D⁵= 125.0 (c = 1.0, CHCl₃);

¹H NMR (500 MHz, CDCl₃):

δ 8.09 (d, J = 7.3 Hz, 2H), 7.97 (d, J = 7.3 Hz, 2H), 7.76 (d,

J = 7.4 Hz, 2H), 7.59 (t, J = 7.4 Hz, 1H), 7.53–7.43 (m,3H), 7.38 (m, 3H), 7.21 (t, J = 7.7 Hz,

2H), 5.97 (d, J = 10.4 Hz, 1H), 5.77 (dd, J = 10.4, 8.0 Hz, 1H), 5.69 (d, J = 3.3 Hz, 1H), 5.54

(dd, J = 10.3, 2.7 Hz, 1H), 5.49 (dd, J = 10.5, 3.4 Hz, 1H), 4.71 (d, J = 7.9 Hz, 1H), 4.00 (dd,

J = 12.7, 6.2 Hz, 1H), 3.86 (d, J = 7.9 Hz, 1H), 3.73 (d, J = 11.5 Hz, 1H), 3.66 (d, J = 11.6 Hz,

1H), 3.55 (dd, J = 11.5, 4.6 Hz, 1H), 3.44 (d, J = 8.0 Hz, 1H), 2.68 (m, 1H), 1.33 (d, J = 6.3 Hz,

3H), 1.22 (s, 9H), 1.15 (s, 3H), 0.95 (s, 3H), 0.93 (s, 3H), 0.91 (s, 3H), 0.86 (s, 3H), 0.59 (s, 3H).

¹³C NMR (125 MHz, CDCl₃):

δ 212.98, 177.29, 166.18, 165.78, 165.40, 133.47, 133.34, 133.25,

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133.15, 130.12, 129.90, 129.80, 129.38, 129.20, 128.97, 128.79, 128.59, 128.50, 128.32, 103.28,

84.14, 82.61, 75.52, 72.28, 71.17, 69.96, 69.64, 64.51, 56.27, 54.99, 52.70, 49.57, 47.63, 44.38,

42.25, 41.70, 39.07, 38.87, 38.26, 35.91, 35.49, 33.36, 31.61, 31.00, 27.47, 25.43, 24.25, 23.23,

20.06, 19.49, 17.96, 17.17, 16.56, 12.04. ESI-HRMS (m/z) calcd for C₆₂H₇₆NaO₁₂[M + Na]⁺

1035.5229, found 1035.5219.

3.2.21. Synthesis of Prosaikogenin G (4)

To a stirred solution of compound 26 (90 mg, 0.09 mmol) in i-PrOH (3 mL) at

−

20 ^◦C,

NaBH₄(7 mg, 0.18 mmol) was added. The mixture was stirred for 3 h, the solution was

quenched by addition of saturated NH₄Cl solution and diluted with brine and extracted

with CH₂Cl₂. The extract was dried over anhydrous Na₂SO₄, ﬁltered, and concentrated

in vacuo. The residue was puriﬁed by silica gel column chromatography (petroleum

ether/EtOAc = 8:1) to give the 16-OH product (86 mg, 95%) as a white foam.

To a stirred solution of the above product (70 mg, 0.07 mmol) in MeOH (3 mL), KOH

(193 mg, 3.5 mmol) was added at room temperature. The mixture was stirred at 55 ^◦C for

24 h before it was quenched with acetic acid. The mixture concentrated under vacuum. The

residue was puriﬁed by reversed-phase silica gel column chromatography (ODS RP-18)

(CHCl₃/MeOH = 5:1) to give prosaikogenin G (

(silica, CHCl₃/MeOH = 4:1); [α]²_D⁵= 54.1 (c = 1.0, CH₃OH); ¹H NMR (500 MHz, pyridine-

d₅): 6.30 (d, J = 4.0 Hz, 1H), 6.07 (d, J = 10.4 Hz, 1H), 5.72 (dd, J = 10.2, 2.6 Hz, 1H), 4.99 (d,

4) (35 mg, 83%) as a white powder. R_f= 0.6

δ

J = 7.7 Hz, 1H), 4.38 (t, J = 8.4 Hz, 2H), 4.32 (dd, J = 11.8, 4.5 Hz, 1H), 3.79 (q, J = 6.3 Hz,

1H), 3.72 (d, J = 9.5 Hz, 1H), 3.60(d, J = 7.0 Hz, 1H), 3.35 (d, J = 7.0 Hz, 1H), 2.72–2.65 (m,

1H), 2.53 (m, 1H), 2.40 (m, 1H), 1.64 (s, 3H), 1.56 (d, J = 6.4 Hz, 3H), 1.38 (s, 3H), 1.06 (s, 3H),

1.04 (s, 3H), 0.98 (s, 3H), 0.96 (s, 3H). ¹³C NMR (125 MHz, pyridine-d₅):

δ 132.52, 132.45,

106.80, 85.38, 82.20, 78.30, 77.61, 75.99, 73.47, 73.32, 71.77, 64.84, 53.52, 51.84, 47.94, 45.83,

44.20, 44.09, 42.38, 39.14, 38.87, 37.31, 36.82, 35.94, 34.25, 32.39, 32.04, 31.79, 26.52, 24.90,

20.06, 19.37, 18.60, 18.08, 17.97, 13.55. ESI-HRMS (m/z) calcd for C₃₆H₅₈NaO₈[M + Na]⁺

641.4024, found 641.4050.

3.2.22. Synthesis of Prosaikogenin (6)

To a stirred solution of the compound 26 (100 mg, 0.1 mmol) in MeOH (3 mL), KOH

◦

(360 mg, 5 mmol) was added at room temperature. The mixture was stirred at 55 C

for 24 h before it was quenched with acetic acid. The mixture was concentrated under

vacuum. The residue was puriﬁed by reversed-phase silica gel column chromatography

(ODS RP-18) (MeOH/H₂O = 5:1) to give compound prosaikogenin (

white powder. R_f= 0.6 (silica, MeOH/H₂O = 4:1); [α]²_D⁵= 13.3 (c = 1.0, MeOH); ¹H NMR

(500 MHz, pyridine-d₅): 6.06 (t, J = 17.8 Hz, 1H), 5.72 (dd, J = 10.3, 2.8 Hz, 1H), 4.99 (d,

6) (57 mg, 93%) as a

δ

J = 7.7 Hz, 1H), 4.43–4.35 (m, 1H), 4.32 (dd, J = 11.9, 4.6 Hz, 1H), 4.08–3.99 (m, 1H), 3.94 (d,

J = 7.8 Hz, 1H), 3.78 (q, J = 6.4 Hz, 1H), 3.71 (d, J = 10.8 Hz, 1H), 3.53 (d, J = 7.9 Hz, 1H), 2.85

(d, J = 14.4 Hz, 1H), 1.55 (d, J = 6.4 Hz, 1H), 1.39 (s, 1H), 1.03 (s, 1H), 1.00 (s, 1H), 0.93 (s, 1H),

0.87 (s, 1H), 0.82 (s, 1H). ¹³C NMR (125 MHz, pyridine-d₅):

δ 212.79, 133.70, 129.96, 106.87,

84.74, 81.88, 75.90, 73.38, 73.25, 71.75, 64.55, 56.85, 55.57, 53.27, 50.27, 47.74, 45.25, 44.16,

42.57, 39.44, 39.00, 36.72, 36.36, 33.80, 32.13, 31.82, 26.49, 24.98, 23.60, 20.71, 20.29, 19.13,

18.01, 17.90, 13.52. ESI-HRMS (m/z) calcd for C₄₂H₆₇O₁₃[M]⁺639.3867, found 639.3869.

3.2.23. Synthesis of Compound 27

To a stirred solution of the compound 10 (225 mg, 0.4 mmol) in MeOH (3 mL), CH₃ONa

(12 mg, 0.2 mmol) was added. The mixture was stirred at room temperature for 8 h before

it was quenched with acid resin until pH = 7. The mixture was ﬁltered through a pad of

celite and washed with MeOH. The ﬁltrate was concentrated under vacuum.

To a stirred mixture of the above product in pyridine (5 mL), triphenylmethyl chloride

(1.04 g, 3.8 mmol) and DMAP (45 mg, 0.4 mmol) were added. The mixture was stirred for

◦

8 h at 75 C, then benzoyl chloride (0.43 mL, 3.8 mmol) was added in the ﬂask at 0 C. The

mixture was stirred for 4 h at room temperature, the solution was quenched by addition of

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saturated NaHCO₃solution, diluted with brine and extracted with CH₂Cl₂. The combined

organic phases were dried over anhydrous Na₂SO₄, ﬁltered, and concentrated in vacuo. The

residue was puriﬁed by silica gel column chromatography (petroleum ether/EtOAc = 5:1

)

to give compound 27 (431 mg, 97%) as a white foam. R_f= 0.3 (silica, PE/EtOAc = 4:1);

[α]²_D⁵= 50.0 (c = 1.0, CHCl₃); ¹H NMR (500 MHz, CDCl₃):

δ 8.19 (d, J = 8.0 Hz, 2H), 8.14

(d, J = 7.4 Hz, 1H), 7.99 (d, J = 8.1 Hz, 2H), 7.73 (t, J = 6.2 Hz, 3H), 7.63 (m, 2H), 7.57–7.46

(m, 11H), 7.43–7.28 (m, 6H), 7.25–7.19 (m, 4H), 7.14 (m, 3H), 7.01–6.92 (m, 4H), 6.81 (d,

J = 8.4 Hz, 2H), 5.99 (s, 1H), 5.80 (d, J = 3.4 Hz, 1H), 5.72 (m, 1H), 5.54 (m, 2H), 5.43 (m, 1H),

5.20 (d, J = 7.6 Hz, 1H), 4.96–4.88 (m, 1H), 4.48 (d, J = 6.0 Hz, 1H), 3.96–3.90 (m, 1H), 3.76 (s,

3H), 3.62–3.54 (m, 1H), 3.30 (d, J = 10.5 Hz, 1H), 1.23 (d, J = 6.0 Hz, 3H). ¹³C NMR (125 MHz,

CDCl₃):

δ 166.30, 165.85, 165.60, 164.97, 164.63, 155.40, 151.01, 143.74, 133.71, 133.53, 133.21,

133.17, 133.09, 132.62, 130.26, 130.23, 130.06, 129.80, 129.77, 129.74, 129.38, 129.28, 129.10,

128.99, 128.89, 128.70, 128.66, 128.56, 128.47, 128.30, 128.27, 128.00, 127.97, 127.13, 118.54,

114.72, 102.05, 96.66, 87.00, 74.24, 74.13, 73.26, 73.23, 72.06, 71.17, 70.04, 66.39, 62.90, 55.72,

16.50. ESI-HRMS (m/z) calcd for C₇₃H₆₂NaO₁₆[M + Na]⁺1217.3930, found 1217.3938.

3.2.24. Synthesis of Compound 29

To a stirred solution of compound 27 (420 mg, 0.4 mmol), 28 (438 mg, 0.7 mmol), and

4Å molecular sieves (400 mg) in CH₂Cl₂(4 mL), TfOH (62 µL, 0.7 mmol) was added at

−20 ^◦C. The mixture was stirred at the same temperature for 1.5 h before it was quenched

with NEt₃(5.0 mL). The mixture was ﬁltered through a pad of celite and washed with

CH₂Cl₂(3

by ﬂash column chromatography (petroleum ether/EtOAc = 3:1) to give compound 29

400 mg, 74%) as an orange foam. R_f= 0.3 (silica, PE/EtOAc = 4:1); [α]²_D⁵= 21.2 (c = 0.25,

CHCl₃); ¹H NMR (500 MHz, CDCl₃):

8.17 (d, J = 8.0 Hz, 2H), 8.14–8.07 (m, 4H), 7.89 (d,

×

2 mL). The ﬁltrate was concentrated under vacuum. The residue was puriﬁed

(

δ

J = 7.9 Hz, 2H), 7.83 (m, 4H), 7.78 (d, J = 7.9 Hz, 2H), 7.66–7.61 (m, 3H), 7.61–7.28 (m, 23H),

7.20 (t, J = 7.5 Hz, 1H), 7.16 (t, J = 7.8 Hz, 2H), 7.04 (d, J = 8.9 Hz, 2H), 6.87 (t, J = 7.7 Hz, 2H),

6.77 (d, J = 9.0 Hz, 2H), 6.00–5.90 (m, 2H), 5.82 (d, J = 3.6 Hz, 1H), 5.74 (t, J = 9.5 Hz, 1H),

5.66 (t, J = 9.8 Hz, 1H), 5.57 (dd, J = 11.6, 6.1 Hz, 1H), 5.48–5.42 (m, 2H), 5.24 (m, 2H), 4.89 (d,

J = 6.1 Hz, 1H), 4.83 (d, J = 7.7 Hz, 1H), 4.73 (m, 2H), 4.58–4.47 (m, 2H), 4.09 (m, 1H), 4.00

(m, 1H), 3.94 (d, J = 8.1 Hz, 1H), 3.72 (s, 3H), 1.39 (d, J = 6.2 Hz, 3H). ¹³C NMR (125 MHz,

CDCl₃):

δ 166.68, 166.30, 165.88, 165.74, 165.52, 165.40, 165.32, 165.20, 164.58, 155.65, 150.88,

133.60, 133.55, 133.51, 133.41, 133.32, 133.24, 133.20, 132.64, 130.35, 129.99, 129.92, 129.86,

129.80, 129.67, 129.40, 129.27, 129.03, 128.86, 128.80, 128.68, 128.65, 128.59, 128.56, 128.52,

128.47, 128.42, 128.26, 127.93, 119.74, 114.71, 102.25, 101.31, 97.14, 75.51, 75.12, 73.91, 73.00,

72.50, 72.34, 71.66, 71.16, 69.41, 69.31, 65.85, 63.14, 55.66, 16.66. ESI-HRMS (m/z) calcd for

C₈₈H₇₄NaO₂₅[M + Na]⁺1553.4411, found 1553.4409.

3.2.25. Synthesis of Compound 30

To a stirred solution of compound 29 (350 mg, 0.2 mmol) in CH₃CN/H₂O (2 mL/0.5 mL),

ceric ammonium nitrate (275 mg, 0.5 mmol) was added. The mixture was stirred at 0 ^◦C for

2 h before it was quenched with NaHCO₃and extracted with EtOAc. The combined organic

phases were washed with brine, dried over anhydrous Na₂SO₄, ﬁltered, and concentrated

under vacuum. The residue was puriﬁed by ﬂash column chromatography (petroleum

ether/EtOAc = 2:1) to give the lactol (266 mg, 81%) as an orange foam. The

were difﬁcult to separate.

α/β anomers

The lactol (230 mg, 0.16 mmol), ortho-(cyclopropylethynyl) benzoic acid (42 mg,

0.24 mmol), EDCI (44 mg, 0.2 mmol) and DMAP (6 mg, 0.05 mmol) were dissolved in

CH₂Cl₂(5 mL). The mixture was stirred at room temperature for 4 h and concentrated un-

der vacuum. The residue was puriﬁed by ﬂash chromatography (petroleum/EtOAc = 3:1

)

to give compound 30 (250 mg, 99%) as a white foam. R_f= 0.3 (silica, PE/EtOAc = 2:1); The

α/β anomers were difﬁcult to separate.

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3.2.26. Synthesis of Compound 31

To a stirred mixture of compound 30 (220 mg, 0.14 mmol), compound 17 (68 mg,

0.1 mmol), and 4Å molecular sieves (300 mg) in CH₂Cl₂(3 mL), PPh₃AuNTf₂(16 mg,

0.03 mmol) was added. The mixture was stirred at 0 ^◦C for 1 h before it was quenched

with NEt₃. The mixture was ﬁltered through a pad of celite and washed with EtOAc.

The ﬁltrate was concentrated under vacuum. The residue was puriﬁed by ﬂash column

chromatography (petroleum ether/EtOAc = 4:1) to give compound 31 (171 mg, 79%) as

a white foam. R_f= 0.3 (silica, PE/EtOAc = 4:1); [α]²_D⁵= 36.3 (c = 1, CHCl₃); H NMR

1

(500 MHz, CDCl₃): δ 8.14 (d, J = 7.4 Hz, 2H), 8.05 (m, 4H), 7.89 (d, J = 7.6 Hz, 2H), 7.85 (d,

J = 7.5 Hz, 2H), 7.81 (d, J = 7.5 Hz, 2H), 7.68–7.51 (m, 9H), 7.44 (m, 10H), 7.38–7.27 (m, 10H),

7.13 (t, J = 7.8 Hz, 2H), 7.01 (t, J = 7.7 Hz, 2H), 5.92 (d, J = 9.6 Hz, 1H), 5.90–5.84 (m, 1H),

5.68 (m, 2H), 5.53 (t, J = 9.7 Hz, 1H), 5.47 (m, 2H), 5.42–5.38 (m, 1H), 5.35 (d, J = 7.9 Hz,

2H), 5.14 (td, J = 9.9, 4.5 Hz, 2H), 4.69–4.61 (m, 2H), 4.54–4.46 (m, 2H), 4.45–4.40 (m, 1H),

4.08 (dd, J = 9.9, 3.7 Hz, 1H), 3.96 (d, J = 6.9 Hz, 4H), 3.56 (d, J = 11.5 Hz, 1H), 3.46 (m, 2H),

3.19 (d, J = 7.2 Hz, 1H), 1.37 (d, J = 6.2 Hz, 3H), 1.25 (s, 3H), 1.18 (s, 9H), 1.10 (s, 9H), 1.03

(s, 3H), 0.97 (s, 3H), 0.94 (s, 3H), 0.87 (s, 3H), 0.85 (s, 3H). ¹³C NMR (125 MHz, CDCl₃):

δ

178.28, 177.34, 166.86, 166.28, 165.96, 165.68, 165.32, 165.23, 164.61, 164.46, 133.70, 133.56,

133.23, 132.72, 130.49, 129.96, 129.91, 129.85, 129.75, 129.65, 129.53, 129.27, 128.94, 128.90,

128.73, 128.68, 128.56, 128.52, 128.45, 128.34, 128.22, 127.96, 102.90, 101.81, 101.15, 83.94,

81.91, 78.18, 75.11, 73.41, 73.11, 72.71, 72.39, 72.31, 71.87, 71.59, 69.64, 69.47, 69.38, 68.30,

63.13, 52.78, 51.70, 47.46, 45.42, 45.27, 42.13, 41.75, 39.06, 38.99, 37.43, 35.85, 34.18, 33.47,

31.64, 31.52, 30.96, 29.83, 27.48, 27.32, 25.34, 23.77, 20.48, 19.56, 17.93, 17.22, 17.03, 12.01.

ESI-HRMS (m/z) calcd for C₁₂₁H₁₃₀NaO₂₉[M + Na]⁺2069.8595, found 2069.8590.

3.2.27. Synthesis of Clinoposaponin I (7)

To a stirred solution of the compound 31 (51mg, 0.02 mmol) in MeOH (3 mL),

◦

KOH (111 mg, 2.0 mmol) was added. The mixture was stirred at 55 C for 24 h be-

fore it was quenched with acetic acid. The mixture concentrated under vacuum. The

residue was puriﬁed by reversed-phase silica gel column chromatography (ODS RP-18)

(

MeOH/H₂O = 2:1) to give compound

silica, MeOH/H₂O = 2:1); [α]²_D⁵= 28.5 (c = 0.25, CH₃OH); ¹H NMR (500 MHz, pyridine-d₅):

6.01 (m, 1H), 5.69 (dd, J = 10.3, 2.8 Hz, 1H), 5.28 (d, J = 7.8 Hz, 1H), 5.09 (d, J = 7.7 Hz, 3H),

7 (21 mg, 89%) as a white powder. R_f= 0.5 (reverse

δ

5.00 (d, J = 7.8 Hz, 1H), 4.86 (d, J = 10.9 Hz, 1H), 4.53 (m, 1H), 4.45–4.37 (m, 3H), 4.28 (dt,

J = 11.9, 5.9 Hz, 3H), 4.22 (t, J = 8.0 Hz, 2H), 4.19–3.98 (m, 5H), 3.89 (dd, J = 11.7, 5.1 Hz, 2H),

3.72 (d, J = 10.6 Hz, 1H), 3.37 (d, J = 6.9 Hz, 1H), 2.52 (m, 1H), 2.32 (d, J = 9.8 Hz, 1H), 1.52

(d, J = 6.3 Hz, 3H), 1.41 (s, 3H), 1.12 (s, 3H), 1.00 (s, 3H), 0.94 (s, 3H), 0.93 (s, 3H), 0.91 (s,

3H). ¹³C NMR (125 MHz, pyridine-d₅):

δ 132.68, 131.67, 106.73, 106.59, 105.98, 85.42, 84.47,

82.12, 78.88, 77.81, 75.99, 75.79, 73.52, 72.59, 72.18, 71.97, 71.52, 64.52, 63.06, 53.59, 52.62,

50.18, 47.82, 47.49, 46.11, 44.20, 42.68, 39.14, 38.20, 36.75, 34.13, 32.10, 26.26, 24.31, 21.34,

20.56, 19.24, 17.82, 13.53. ESI-HRMS (m/z) calcd for C₄₈H₇₈NaO₁₈[M + Na]⁺965.5080,

found 965.5077.

4. Conclusions

Here, we report the facile synthesis of seven saikosaponins; namely, saikosaponin

A (

1), D (2), prosaikosaponin F (3), G (4), saikosaponin Y (5), prosaikogenin (6), and

clinoposaponin I (

7), which have been identiﬁed from Radix Bupleuri, a common traditional

Chinese medicine and relevant plants. These mono-, di-, and trisaccharide saponins feature

triterpene aglycones of high oxidation states, which bear 13,28-epoxy-ether moiety and oxo

groups at C16 and C23. The methods previously developed for the selective hydroxylation

of the triterpenes of low oxidation states, such as oleanolic acid, have enabled the present

synthesis. In addition, the gold(I)-catalyzed glycosylation with o-alkynylbenzoates as

donors has been applied successfully in the present synthesis. Given the conserved nature

of the structures of saikosaponins, the work reported herein offers the prospect of being able

to access many more members of saikosaponins and their natural and synthetic analogs,

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thus facilitating in-depth studies on biological and pharmacological activities of these

components of folk medicines.

Supplementary Materials: The following are available online at https://ww w .mdpi.com/article/10

.3390/molecules26071941/s1. Copies of NMR spectra of compounds 1–7, 10–12, 14–27, 29 and 31.

Author Contributions: Conceptualization, P.X. and B.Y.; methodology, Z.W. and B.W.; formal analy-

sis, Z.W. and T.M.; investigation, Z.W.; resources, B.Y.; data curation, Z.W.; writing—original draft

preparation, Z.W. and P.X.; writing—review and editing, B.Y.; visualization, Z.W.; supervision, B.Y.;

project administration, P.X. and B.Y.; funding acquisition, B.Y. All authors have read and agreed to

the published version of the manuscript.

Funding: This research was funded by Shanghai Municipal Science and Technology Major Project,

National Natural Science Foundation of China (22031011 & 21621002), Key Research Program of Fron-

tier Sciences of CAS (ZDBS-LY-SLH030), Strategic Priority Research Program of CAS (XDB20020000),

and Youth Innovation Promotion Association of CAS (2020258).

Institutional Review Board Statement: Not applicable.

Informed Consent Statement: Not applicable.

Data Availability Statement: The data presented in this study are available in the article and

Supplementary Material.

Conﬂicts of Interest: The authors declare no conﬂict of interest.

Sample Availability: Samples of the compounds 1–7 are available from the authors.

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Article Doi

Facile synthesis of saikosaponins

DOI: 10.3390/molecules26071941

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