Qualitative evaluation of regioselectivity in the formation of di- And tri-6-O-tritylates of α-cyclodextrin

Article abstract of DOI:10.3762/bjoc.11.168

The quantitative analysis of reaction products showed that the reaction of 6A,6D-di-O-trityl-α-cyclodextrin (CD), AD-isomer, with trityl chloride in pyridine at 55 °C gave 6A,6B,6E-tri-O-trityl-α-CD, the amount of which was only 25% of that of simultaneou

Full text of DOI:10.3762/bjoc.11.168

Qualitative evaluation of regioselectivity in the formation of
di- and tri-6-O-tritylates of α-cyclodextrin
Keisuke Yoshikiyo*, Yoshihisa Matsui and Tatsuyuki Yamamoto
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2015, 11, 1530–1540.
Faculty of Life and Environmental Science, Shimane University, 1060
Nishikawatsu, Matsue, Shimane, 690-8504, Japan
doi:10.3762/bjoc.11.168
Received: 20 May 2015
Email:
Accepted: 11 August 2015
Published: 02 September 2015
Keisuke Yoshikiyo* - yoshikiyo@life.shimane-u.ac.jp
* Corresponding author
This article is part of the Thematic Series "Superstructures with
cyclodextrins: Chemistry and applications III".
Keywords:
1H and 13C NMR spectroscopy; quantitative analysis; regioselectivity;
tritylation; ultra-fast liquid chromatography (UFLC)
Guest Editor: G. Wenz
© 2015 Yoshikiyo et al; licensee Beilstein-Institut.
License and terms: see end of document.
Abstract
The quantitative analysis of reaction products showed that the reaction of 6A,6D-di-O-trityl-α-cyclodextrin (CD), AD-isomer, with
trityl chloride in pyridine at 55 °C gave 6A,6B,6E-tri-O-trityl-α-CD, the amount of which was only 25% of that of simultaneously
formed 6A,6B,6D-tri-O-trityl-α-CD. This indicates that the bulky trityl groups of glucopyranose-A and -D (Glu-A and -D, respect-
ively) in the AD-isomer mainly retard the additional tritylation of the C(6)-OH of the adjacent glucopyranoses in a counter-clock-
wise direction (Glu-F and -C, respectively). 1H NMR spectra of the AD-isomer showed that the O(6)-H and C(6)-H signals of
Glu-C and -F are shifted upfield due to the ring current of the trityl groups. Thus, it is concluded that the bulky trityl groups on
Glu-A and Glu-D are oriented to Glu-F and Glu-C, respectively, and sterically retard additional tritylation on Glu-F and Glu-C.
Similar steric hindrance was also observed in the additional tritylations of mono-6-O-trityl-α-CD, 6A,6B-di- and 6A,6C-di-O-trityl-
α-CD’s.
Introduction
Regioselective modification and deprotection on the primary functionalized CD derevatives [6-19]. CDs have hydroxy
hydroxy side of cyclodextrins (CDs) are of great importance in groups at the 2-, 3- and 6-positions of their glucopyranose (Glu)
supramolecular chemistry, as they allow the preparation of residues. However, the reaction of CD with trityl chloride in
sophisticated concave molecules such as multi- or hetero-func- pyridine gives exclusively 6-O-substituted CD. CD is composed
tionalized CD derivatives that are important intermediates for of six (α-CD), seven (β-CD), eight (γ-CD), or more Glu
the preparation of enzyme mimics [1-5]. The tritylation of residues. Thus, a reaction of α-CD, for example, with trityl
cyclodextrin (CD) has attracted much attention, since the trity- chloride (TrCl) gives mono- [7], di- [13,15,16], tri- [9,11], tetra-
lates are useful intermediates for the preparation of a variety of [18], and per-6-O-trityl derivatives [19]. The di-6-O-tritylate of
1530

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
α-CD involves three regioisomers, that are, 6A,6B-, 6A,6C-, and
6A,6D-di-O-tritylates (AB-, AC-, and AD-isomers,
respectively), as shown in Scheme 1. These regioisomers were
well separated and characterized [13]. The tri-6-O-tritylate of
α-CD involves four regioisomers, that are 6A,6B,6C-, 6A,6B,6D-,
6A,6B,6E-, and 6A,6C,6E-tri-O-tritylates (ABC-, ABD-, ABE-,
and ACE-isomers, respectively, Scheme 1). Among them, only
a symmetrical molecule of the ACE-isomer was separated and
characterized [9]. The tetratritylate of α-CD involves three
regioisomers, among which 6A,6B,6D,6E-tetra-O-tritylate was
separated and characterized [18]. The trityl group is so bulky
that the additional tritylation of C(6)-OH on Glu adjacent to a
previously tritylated Glu is considered to be sterically hindered.
Thus, a reaction of α-CD with 3.3 equivalents TrCl in pyridine
at 55 °C gave selectively the ACE-isomer in good yield (23%)
[9]. However, the regioselectivity in the formation of di- or tri-
6-O-trityl-α-CD has not always been quantitatively evaluated.
The present work deals with the analysis of products in the
reaction of α-CD, as well as mono- and di-6-O-trityl-α-CD’s,
with TrCl in pyridine to evaluate quantitiatively the steric effect
of the bulky trityl group on the regioselectivity of the reaction.
For the sake of clarity, it must be noted here that letters from A
to F that identify individual glucopyranose units are numbered
along with the α1→4 linkage direction, and that the term
“clockwise direction” refers to the direction when viewed from
the secondary hydroxy side, as shown in Scheme 1.
Results and Discussion
Identification of di- and tri-6-O-tritylates of
α-CD
Mono-, di-, and tri-6-O-tritylates of α-CD were prepared by a
reaction of α-CD with TrCl in pyridine at 55 °C according to
the direction of literature [9], and separated by means of
reversed-phase column chromatography. Three regioisomers of
di-6-O-trityl-α-CD obtained gave well-separated peaks in
UFLC (ultra-fast liquid chromatography) experiment (Figure 1),
details of which will be described in the Experimental part.
Four regioisomers of tri-6-O-trityl-α-CD also gave well-sep-
arated peaks in the UFLC chromatography (Figure 2), when
acetonitrile/methanol/water (40/45/15, v/v/v) was used as an
eluent. The di-6-O-trityl-α-CD regioisomers which gave the
first, second, and third peaks in the UFLC chromatogram
afforded well-defined 13C NMR spectra (Figure 3a, b, and c,
respectively) in dimethyl sulfoxide-d6 (DMSO-d6) at 50 °C.
Tanimoto, et al. [13], have already reported the 13C NMR
spectra of the isomers measured in C5D5N. On the basis of a
comparison of their spectra with ours, we assigned that the
isomers which gave the first, second, and third peaks in the
UFLC chromatogram are the AD-, AC-, and AB-isomers, res-
pectively. This assignment was confirmed by UFLC analysis on
the products of reactions of these three regioisomers with TrCl
Scheme 1: Tritylates of α-CD examined in the present study and the
reaction pathway. Letters A to F represent the glucopyranose units
along with α1-4 linkage direction, numbered when viewed from the
secondary hydroxy group side.
Figure 1: UFLC chromatogram of three regioismers of di-6-O-trityl-α-
CD with 50% aqueous acetonitrile as an eluent.
1531

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
AD-isomer by 13C NMR spectroscopy gave only two (the first
and second) peaks in UFLC analysis, whereas those assigned to
be AB- and AC-isomers by 13C NMR gave three (the first,
second, and third) and four (the first, second, third, and fourth)
peaks, respectively, in UFLC analysis. These results are in
accord with the reaction pathway shown in Scheme 1. A similar
method had been used for the identification of di- and tri-6-O-
mesitylenesulfonyl-α-CD [20]. Scheme 1 also shows that the
ACE-isomer is formed only by the reaction of the AC-isomer
with TrCl, and we assigned that the fourth peak in UFLC chro-
matogram is due to the ACE-isomer. On the other hand, the
ABC-isomer is not formed by the reaction of the AD-isomer
with TrCl and is formed by the reactions of AC- and
AB-isomers with TrCl. Thus, we assigned that the third peak is
due to the ABC-isomer [20]. It is difficult to determine by
UFLC analysis which of the ABD- or ABE-isomer gives the
Figure 2: UFLC chromatogram of four regioisomers of tri-6-O-trityl-α-
CD with an eluent of acetonitrile/methanol/water (40:45:15, v/v/v).
to give tri-6-O-trityl-α-CD. As Scheme 1 shows, the reaction of first or the second peak in UFLC. Here, we noted that 6A,6B,6D-
AD-isomer with TrCl gives only two tri-tritylates of ABD- and and 6A,6B,6E-tri-6-O-mesitylenesulfonyl-α-CD’s have already
ABE-isomers. On the other hand, the additional tritylation of been identified by 1H NMR spectroscopy [21,22]. Then, we
AB- and AC-isomers gives three (ABC-, ABD-, and ABE-) and tried to convert a regioisomer of tri-6-O-tritylates, which gave
four (ABC-, ABD-, ABE-, and ACE-) isomers, respectively. In the first peak in UFLC, to tri-6-O-mesitylenesulfonyl-α-CD.
practice, the additional tritylation of a ditritylate assigned to be The conversion pathway is shown in Scheme 2, where all the
Figure 3: A part of 13C NMR spectra of di-6-O-trityl-α-CD in DMSO-d6 at 50 °C a) AD-isomer, b) AC-isomer, and c) AB-isomer.
1532

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
Scheme 2: A pathway of the conversion of a regioisomer of tri-6-O-trityl-α-CD (ABE isomer) to the corresponding tri-6-O-mesitylenesulfonyl-α-CD.
Letters A to F represent the glucopyranose units, numbered in a clockwise direction when viewed from the secondary hydroxy group side. Abbrevia-
tions: Tr: trityl, Bn: benzyl, and Mess: mesitylenesulfonyl.
hydroxy groups of the regioisomer were substituted by benzy- Similar conversion of tri-6-O-trityl-α-CD to tri-6-O-mesitylene-
loxy groups, and the resulting per-benzylated compound was sulfonyl-α-CD was carried out for a regioisomer which gave the
treated with conc. HCl to remove the trityl groups. The three second peak in UFLC, and the 1H NMR spectrum of the
hydroxy groups formed were mesitylenesulfonylated, and obtained mesitylenesulfonylate coincided with that of authentic
finally, the benzyl groups were removed by hydrogenation with 6A,6B,6D-tri-6-O-mesitylenesulfonyl-α-CD. Thus, we
Pd/C to form tri-6-O-mesitylenesulfonyl-α-CD. The retention concluded that the regioisomers which gave the first and second
time in UFLC and the 1H NMR spectrum of the obtained peaks in UFLC are the ABE- and ABD-isomers, respectively.
mesitylenesulfonylate coincided with those of authentic The 13C NMR spectra for the four regioisomers of tri-6-O-
6A,6B,6E-tri-6-O-mesitylenesulfonyl-α-CD, respectively. trityl-α-CD in DMSO-d6 at 50 °C are illustrated in Figure 4.
1533

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
Figure 4: A part of 13C NMR spectra of tri-6-O-trityl-α-CD in DMSO-d6 at 50 °C. a) ABE-isomer, b) ABD-isomer, c) ABC-isomer, and d) ACE-isomer.
Regioselectivity in the formation of di- and tri-
6-O-trityl-α-CD
Dried α-CD was allowed to react with TrCl in pyridine at 55 °C,
and aliquots were withdrawn at hourly intervals to determine
the concentrations of products by means of the UFLC analysis.
The concentrations of mono-6-O-trityl-α-CD, α-CD(Tr)1, and
three regioisomers of ditritylates formed are plotted against
reaction time in Figure 5. The concentration of α-CD(Tr)1
smoothly increased with time. On the other hand, the concentra-
tions of di-6-O-tritylates of α-CD were low at the beginning of
the reaction and gradually increased with time, suggesting that
the ditritylates are formed by additional tritylation of the previ-
ously formed α-CD(Tr)1. If the reactivities of the C(6)-OH
groups on the Glu residues of α-CD(Tr)1 are equal to each
other, AB- and AC-isomers would be produced in equal amount
and in twice that of AD-isomer. In practice, the molar ratio of
Figure 5: Time-course of the formation of mono- (left ordinate) and
the products was about 0.40 ± 0.01:1.00:0.52 ± 0.01
(AB:AC:AD) in every aliquot. The AB-isomer was produced
considerably less than the AC-isomer.
di-6-O-tritylates (right ordinate) of α-CD in a reaction of α-CD with TrCl
in pyridine at 55 °C. Average mole ratio of AB:AC:AD =
0.40 ± 0.01:1.00:0.52 ± 0.02.
In order to investigate the formation of the ditritylates in detail, AB:AC:AD was 0.43 ± 0.01:1.00:0.50 ± 0.01, virtually the
α-CD(Tr)1 was directly tritylated in pyridine at 55 °C. Changes same as in the case when α-CD was used as reactant. We also
in concentration of three regioisomers of the ditritylates with tried to determine the concentrations of tri-6-O-tritylates of
time are illustrated in Figure 6. The average mole ratio of α-CD. However, the concentrations were so low that further
1534

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
Figure 6: Time-course of the formation of the regioisomers of di-6-O-
trityl-α-CD in a reaction of α-CD(Tr)1 with TrCl in pyridine at 55 °C.
Average mole ratios of AB:AC:AD = 0.43 ± 0.01:1.00:0.50 ± 0.01.
Figure 7: Time-course of the formation of the regioisomers of tri-6-O-
trityl-α-CD in a reaction of AD-isomer with TrCl in pyridine at 55 °C.
Average mole ratio of ABD:ABE = 1.00:0.25 ± 0.02.
tritylation of the ditritylates to tritritylates did not affect the
mole ratio of the ditritylates. The small mole ratio of AB-isomer
to AC-isomer suggests that the bulky trityl group on α-CD(Tr)1
retards the additional tritylation of the C(6)-OH on the adjacent
Glu-B and/or Glu-F. Glu-B is adjacent to Glu-A in a clockwise
direction, and Glu-F, in a counter-clockwise direction.
Then, we carried out experiments using the AD-isomer as the
reactant to elucidate which of the C(6)-OH of Glu-B or Glu-F is
more restricted in the additional tritylation of α-CD(Tr)1. If the
trityl groups of Glu-A and -D of the AD-isomer retard the addi-
tional tritylation of the adjacent C(6)-OH in a clockwise direc-
tion (Glu-B and -E, respectively), the ABD-isomer will be the
minor product and the ABE-isomer the major one. To the
contrary, if they retard the additional tritylation of the adjacent
C(6)-OH in a counter-clockwise direction (Glu-F and -C, res-
pectively), the ABE-isomer will be the minor product and the
ABD-isomer the major one. The quantitative analysis of the
product in this reaction revealed that the ABE-isomer is formed
in a smaller amount than the ABD-isomer, with a mole ratio of
0.25 ± 0.02:1.00 (Figure 7). This result indicates that the trityl
groups of Glu-A and Glu-D in the AD-isomer mainly retard the
Figure 8: Time-course of the formation of the regioisomers of tri-6-O-
trityl-α-CD in a reaction of AC-isomer with TrCl in pyridine at 55 °C.
Average mole ratio of ABC:ABD:ABE:ACE =
0.17 ± 0.01:0.15 ± 0.01:0.80 ± 0.01:1.00.
additional tritylation of the C(6)-OH of the adjacent Glu in a dine. In AC-isomer, Glu-B, -D, -E, and -F are chemically
counter-clockwise direction (Glu-F and Glu-C, respectively). unequivalent to one another, and additional tritylation gives the
Thus, the trityl group of Glu-A in α-CD(Tr)1 will also mainly four regioisomers of ABC-, ACD-, ACE-, and ACF. In this
retard the additional tritylation of the C(6)-OH of the adjacent context, ACD- and ACF-isomers are identical to ABE- and
Glu in a counter-clockwise direction (Glu-F).
ABD-isomers, respectively. If the additional tritylation occurs
without regioselectivity, these regioisomers should be produced
Figure 8 shows the time-course of the formation of tri-6-O-trity- in an equal yield. In practice, the mole ratios of ABC-, ABD-,
lates of α-CD in the reaction of AC-isomer with TrCl in pyri- ABF-, and ACE-isomers in the reaction mixtures were
1535

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
virtually constant during the reaction time and equal to
0.17 ± 0.01:0.15 ± 0.01:0.80 ± 0.01:1.00. The additional trityla-
tions of the C(6)-OHs on Glu-B and Glu-F, which are adjacent
to Glu-C and Glu-A in a counter-clockwise direction, respect-
ively, were again strongly retarded. Interestingly, the symmetri-
cally substituted ACE-isomer was the major product, in clear
contrast to the case of mesitylenesulfonylation of 6A,6C-di-O-
mesitylenesulfonyl-α-CD, where the ACE-isomer is the minor
product [23].
Figure 9 shows the time-course of the formation of tri-6-O-trity-
lates of α-CD in the reaction of the AB-isomer with TrCl in
pyridine. In the AB-isomer, the additional tritylation of Glu-C
and -F gives the same product, the ABC-isomer. Thus, if the
tritylation occurs without regioselectivity, the mole ratio of
ABC-, ABD-, and ABE-isomers would be 2:1:1. In practice, the
mole ratio was 0.71 ± 0.01:1.00:0.98 ± 0.01. Again, the trityla-
tion of Glu-C and/or Glu-F, which are adjacent to Glu-B and
Glu-A, respectively, was strongly retarded.
Figure 10: 1H NMR spectra of α-CD (a) and the A,D-isomer (b) in
DMSO-d6 at 50 °C.
spectra (Table 1). A 2D ROESY measurement gave a key spec-
trum (Figure 11) used for the assignment. The signal of the
C(1)-H for Glu-A and -D in the F2 axis gave cross-peaks not
only with the C(2)-H (δ 3.36) of the same Glu, but also with the
C(4)-H (δ 3.56) of the adjacent Glu-B and -E. In the same
manner, the signal of C(1)-H for Glu-B and -E gave a cross-
peak with the C(4)-H (δ 3.47) of the adjacent Glu-C and -F, and
that for Glu-C and -F gave a cross-peak with the C(4)-H
(δ 3.37) of the adjacent Glu-D and -A. It is worth noting that the
signal (δ 3.72) of the O(6)-H for Glu-C and -F was fairly
up-field shifted (Δδ = −0.62 ppm) compared with that (δ 4.34)
of α-CD. On the other hand, the signal of the O(6)-H for
Glu-B and -E (δ 4.45) was slightly down-field shifted
Table 1: Chemical shift of A,D-α-CD(tr)2 in DMSO-d6 at 50 °C.
Chemical shift / ppm
Glu(A,D)
Glu(B,E)
Glu(C,F)
Figure 9: Time-course of the formation of the regioisomers of tri-6-O-
trityl-α-CD in a reaction of the AB-isomer with TrCl in pyridine at 55 °C.
Average mole ratios of ABC:ABD:ABE = 0.71 ± 0.01:1.00:0.98 ± 0.01.
C(1)-H
C(2)-H
C(3)-H
C(4)-H
C(5)-H
C(6)-H(a)
C(6)-H(b)
O(2)-H
O(3)-H
O(6)-H
Tr(o)-H
Tr(m)-H
Tr(p)-H
4.92
3.36
3.80
3.37
3.89
3.40
3.02
5.33
5.63
–
4.78
3.31
3.82
3.56
3.75
3.96
3.62
5.44
5.37
4.45
–
4.61
3.23
3.72
3.47
3.68
3.30
2.55
5.68
5.37
3.72
–
1H NMR spectroscopy of the AD-isomer
All the above results shows that the trityl group introduced to
the C(6)-O of α-CD retards additional tritylation of the C(6)-OH
of Glu adjacent to the previously tritylated Glu in a counter-
clockwise direction. In order to confirm this suggestion, we
estimated the orientation of the trityl groups in the AD-isomer
by means of 1H NMR spectroscopy in DMSO-d6 (Figure 10).
The AD-isomer is symmetrical and it is relatively easy to assign
the 1H NMR signals. The spectrum of the AD-isomer was fully
assigned by means of 2D COSY, 2D ROESY, and 2D TOCSY
7.32
7.21
7.13
–
–
–
–
1536

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
(Δδ = 0.11 ppm). The signal (δ 2.55) of one of the C(6)-H’s of presence of CaH2 before use. N,N-Dimethylformamide (DMF)
Glu-C and -F was also significantly shifted up-field was also dried over CaH2 and distilled before use. Acetonitrile
(Δδ = −1.11 ppm) compared with that (δ 3.66) of α-CD. These for high performance liquid chromatography was purchased
significant up-field shifts of the signals of the O(6)-H and C(6)- from Wako Pure Chemical Industries Ltd. DMSO-d6 containing
H for Glu-C and -F are attributable to the ring current of the 0.05% v/v tetramethylsilane (Cambridge Isotope Laboratiories,
phenyl moieties of the trityl groups on Glu-A and -D. Glu-C Inc., 99.9 atom % D) was used for 1H NMR measurements.
and -F are located at counter-clockwise directions from Glu-D
and -A, respectively. Thus, it is reasonable to conclude that the Apparatus
trityl groups on Glu-A and -D are oriented to Glu-F and -C, res- The tritylates of α-CD in a reaction mixture were quantitatively
pectively, and sterically retard additional tritylation of the C(6)- determined by means of a Shimadzu prominence UFLC system,
OHs on Glu-F and -C. Similar steric hindrance will occur in the which was composed of a pair of pumps (LC-20 AD), an auto-
tritylation of α-CD(Tr)1 as well as in the tritylations of AB- and sampler (SIL-20 ACHT), a column oven (CTO-20AC), a photo-
AC-regioisomers.
diode array detector (SPD-M20A), and a system controller
(CBM-20A). Shim-pack XR-ODS (100 mm × 3.0 mm i.d. was
used as a column, through which acetonitrile/water or acetoni-
trile/methanol/water was passed as an eluent. The flow rate of
eluent was 0.5 mL/min, and the eluate was detected at 260 nm.
The column temperature was maintained at 40 °C. Linear stan-
dard curves were prepared between the peak area of the trity-
lates and their concentrations. The 1H and 13C NMR spectra of
the tritylates in DMSO-d6 were recorded on a JEOL Model
JNM-A400 FT NMR spectrometer (400 MHz for 1H and
100 MHz for 13C) with a sample tube of 5.0 mm diameter at
55 °C. Tetramethylsilane was used as an internal reference.
High resolution ESIMS data were obtained using a Waters
Synapt G2 mass spectrometer.
Synthesis of 6-O-tritylates of α-CD
6-O-Tritylates of α-CD were prepared by a reaction of α-CD
with TrCl in pyridine at 55 °C according to a literature proce-
dure [9], and separated by means of column chromatography
with a Lober column LiChroprep RP-18 (Merck, 25 × 310 mm).
Mono-, di-, and tri-6-O-tritylates were separated by the use of
30%, 40–50%, and 60% aqueous acetonitrile solutions, respect-
ively, as eluents. Thin-layer chromagography (TLC) was
carried out with Merck silica gel 60 F254.
Figure 11: A part of 2D ROESY spectrum of the A,D-isomer in
DMSO-d6 at 50 °C.
In conclusion, the bulky trityl group on a tritylate of α-CD is
oriented to the C(6)-OH on the adjacent glucopyranose in a Mono-6-O-trityl-α-CD: 13C NMR (100 MHz, DMSO-d6) δ
counter-clockwise direction and sterically retards the additional 144.03, 128.30, 127.57, 126.72, 102.28, 101.89, 101.85, 101.75,
tritylation of the C(6)-OH.
85.97, 82.70, 82.03, 81.89, 81.84, 80.94, 73.21–73.12, 72.80,
72.21, 72.09–72.05, 71.89, 70.41, 63.08, 60.13, 59.96, 59.84,
58.96 ppm; HRMS–ESI m/z: [M + Na]+ calcd for
C55H74O30Na+, 1237.4163; found, 1237.4150.
Experimental
Materials
The α-CD was supplied by Ensuiko Sugar Refining Co., Ltd.,
Conversion of tri-6-O-trityl-α-CD to tri-6-O-
and dried overnight in vacuo at 110 °C before use. TrCl (Tokyo
Chemical Industry Co., Ltd.), benzyl bromide and mesitylene- mesitylenesuflonyl-α-CD
sulfonyl chloride (Wako Pure Chemical Industries Ltd.) were A regioisomer of tri-6-O-trityl-α-CD (605 mg, 0.356 mmol)
used without further purification. Commercially available NaH which gave the first peak in UFLC was dissolved in DMF
in oil (50–77%) and Pd/C (Pd 10%) were used for the conver- (30 mL). NaH in oil (1.00 g) and benzyl bromide (3.10 g,
sion of tri-6-O-trityl-α-CD to tri-6-O-mesitylenesulfonyl-α-CD. 18.1 mmol) were added to the solution in an ice bath, and the
Reagent-grade pyridine was dried over CaH2 and distilled in the solution was stirred overnight. TLC on silica gel (hexane/ethyl
1537

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
acetate, 2:1) showed a product, having an Rf value of 0.60. The bath (55 °C). TrCl (111 mg, 0.399 mmol for α-CD or 41.5 mg,
reaction mixture was diluted with CHCl3 (100 mL) and washed 0.149 mmol for α-CD(Tr)1) was added to the stirred solution.
with water (100 mL, 4 times). The CHCl3 layer was dried over At hourly intervals, 2.0 mL aliquots were withdrawn and added
CaSO4 and evaporated to dryness. The residue was chro- to 0.5 mL water to stop the reaction. The resulting solution was
matographed over Merck silica gel 60, using hexane/ethyl evaporated to dryness, and the residue was dissolved in 2.0 mL
acetate (2:1) as an eluent. The crude tri-6-O-trityl-per-O-benzyl- methanol. Concentrations of products in the methanol solutions
α-CD (1.32 g) obtained was dissolved in CHCl3 (100 mL), and were determined by UFLC with acetonitrile/water (30:70 and
the solution was vigorously shaken with concentrated HCl 45:55, v/v, for the separation of mono- and ditritylates, respect-
(30 mL) for 10 min to remove the trityl groups. TLC on silica ively) as mobile phase. Retention times of α-CD(Tr)1 and the
gel (hexane/ethyl acetate, 1:1) showed a product, having an Rf AD-, AC-, and AB-isomers were ca. 3.8, 2.7, 6.6, and 9.9 min,
value of 0.55. The CHCl3 layer was washed with water (50 mL, respectively.
3 times), dried over CaSO4, and evaporated to dryness. The
residue was chromatographed over silica gel, using hexane/ 6A,6B-Di-O-trityl-α- CD (AB-isomer): 13C NMR (DMSO-d6)
ethyl acetate (1:1) as an eluent to give a fairly pure product of δ 144.26, 143.80, 128.19, 128.07, 127.66, 127.41, 126.71,
trihydroxy-per-O-benzyl-α-CD (0.48 g, 0.21 mmol). The prod- 126.58, 102.07, 102.00, 101.97, 101.79, 101.59, 101.37, 86.03,
uct was reacted with mesitylenesulfonyl chloride (0.62 g, 85.65, 83.27, 81.67, 81.59, 81.38, 81.34, 80.76, 73.32, 73.22,
2.84 mmol) in pyridine (20 mL). TLC on silica gel (hexane/ 73.14, 72.83, 72.36, 72.30, 72.24, 72.17, 72.11, 72.02, 71.78,
ethyl acetate 1:1) showed a product, having an Rf value of 0.91. 71.22, 70.37, 63.78, 63.19, 59.84, 59.58, 59.17 ppm;
The reaction mixture was evaporated to dryness, and the residue HRMS–ESI (m/z): [M + Na]+ calcd for C74H88O30Na+,
was dissolved in 50 mL of hexane/ethyl acetate (2:1). The solu- 1479.5258; found, 1479.5217.
tion was washed with water (50 mL, 3 times). The organic layer
was dried over CaSO4 and evaporated to dryness. The residue 6A,6C-Di-O-trityl-α- CD (AC-isomer): 13C NMR (DMSO-d6)
was chromatographed over silica gel, using hexane/ethyl acetate δ 144.06, 143.99, 128.34, 128.27, 127.63, 127.53, 126.76,
(2:1) as an eluent to give a fairly pure tri-6-O-mesitylenesul- 126.67, 102.40, 102.10, 101.90, 101.76, 101.59, 86.03, 85.97,
fonyl-per-O-benzyl-α-CD (0.51 g). The product was dissolved 83.12, 82.36, 81.79, 81.70, 81.00, 80.92, 73.25, 73.16, 72.94,
in 5 mL of acetic acid and hydrogenated in the presence of Pd/C 72.74, 72.23, 72.07, 70.56, 70.40, 63.28, 63.04, 59.98, 59.83,
(0.21 g) to remove the benzyl groups of the product. TLC on 59.06, 59.02 ppm;. HRMS–ESI (m/z): [M + Na]+ calcd for
silica gel (butanone/ethanol/H2O, 7:1:1) showed a product, C74H88O30Na+, 1479.5258; found, 1479.5217.
having an Rf value of 0.47, which was equal to that of authentic
tri-6-O-mesitylenesulfonyl-α-CD. The reaction mixture was 6A,6D-Di-O-trityl-α- CD (AD-isomer): 13C NMR (DMSO-d6)
filtered, and the filtrate was evaporated to dryness to give a δ 143.89, 128.29, 127.51, 126.69, 102.41, 101.87, 101.45,
fairly pure tri-6-O-mesitylenesulfonyl-α-CD (0.26 g, 86.06, 83.09, 81.52, 80.82, 73.35, 73.02, 72.89, 72.32, 72.12,
0.17 mmol). The retention time of the product in UFLC with 72.00, 71.85, 70.36, 63.32, 60.02, 58.77 ppm; HRMS–ESI
43% aqueous acetonitrile as an eluent coincided with that of (m/z): [M + Na]+ calcd for C74H88O30Na+, 1479.5258; found,
authentic A,B,E-tri-6-O-mesitylenesulfonyl-α-CD [23]. The 1479.5217.
1H NMR spectrum of the product in DMSO-d6 at 50 °C also
Reaction of AD-, AC-, or AB-isomers with
coincided with that of authentic A,B,E-tri-6-O-mesitylenesul-
fonyl-α-CD [23]. Thus, it was concluded that a regioisomer of TrCl and product analysis
tri-6-O-trityl-α-CD which gave the first peak in UFLC is A,B,E- The AD-isomer (78 mg, 0.053 mmol), AC-isomer (150 mg,
tri-6-O-trityl-α-CD. Similar conversion of a regioisomer of tri- 0.103 mmol), or AB-isomer (151 mg, 0.104 mmol) was
6-O-trityl-α-CD, which gave the second peak in UFLC, to tri-6- dissolved in pyridine (35 mL). The solution was boiled to
O-mesitylenesulfonyl-α-CD was carried out, and the resulting remove a trace amount of water as an azeotropic mixture, and
product was confirmed to be A,B,D-tri-6-O-mesitylenesulfonyl- the resulting solution (25 mL) was stirred in an oil bath (55 °C).
α-CD by 1H NMR spectroscopy.
TrCl (23 mg, 0.083 mmol for AD-isomer, 53 mg, 0.189 mmol
for AC-isomer, or 58 mg, 0.207 mmol for AB-isomer) was
added to the stirred solution. At hourly intervals, 2.0 mL
aliquots were withdrawn, added to 0.5 mL water to stop the
Reaction of α-CD or α-CD(Tr)1 with TrCl and
product analysis
α-CD (202 mg, 0.208 mmol) or α-CD(Tr)1 (102 mg, reaction. The resulting solution was evaporated to dryness, and
0.084 mmol) was dissolved in pyridine (60 mL). The solution the residue was dissolved in 2.0 mL methanol. Concentrations
was boiled to remove trace amounts of water as an azeotropic of products in the methanol solutions were determined by
mixture, and the resulting solution (50 mL) was stirred in an oil UFLC with acetonitrile/methanol/water (40:45:15, v/v/v) as
1538

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
mobile phase for the separation of tri-tritylates formed. Reten- Acknowledgements
sion times of ABE-, ABD-, ABC-, and ACE-isomers were ca. The authors thank the faculty of Life and Environmental
6.2, 7.5, 9.4 and 11.3 min, respectively.
Science in Shimane University for help in financial supports for
publishing this report.
6A,6B,6C-Tri-O-trityl-α-CD (ABC-isomer): 13C NMR
(DMSO-d6) δ 144.32, 144.20, 143.66, 128.24, 128.13,
127.93, 127.71, 127.39, 126.80, 126.61, 126.40, 102.16,
101.93, 101.73, 101.66, 101.59, 101.25, 85.97, 85.78,
85.73, 83.12, 81.78, 81.40, 80.95, 80.83, 80.69, 73.32,
73.18, 73.07, 73.00, 72.62, 72.57, 72.42, 72.28, 72.20,
72.09, 72.05, 71.96, 71.72, 71.35, 70.87, 70.51, 63.69, 63.52,
5 9 . 6 5 , 5 9 . 5 1 , 5 9 . 0 8 p p m ; H R M S – E S I ( m / z ) :
[M + Na]+ calcd for C93H102O30Na+, 1721.6345; found,
1721.6067.
References
1. Tabushi, I.; Kuroda, Y.; Yokota, K.; Yuan, L. C. J. Am. Chem. Soc.
1981, 10, 711–712. doi:10.1021/ja00393a056
2. Bistri, O.; Sinaÿ, P.; Barbero, J. J.; Sollogoub, M. Chem. – Eur. J. 2007,
13, 9757–9774. doi:10.1002/chem.200700971
3. Guieu, S.; Sollogoub, M. J. Org. Chem. 2008, 73, 2819–2828.
doi:10.1021/jo7027085
4. Gramage-Doria, R.; Rodriguez-Lucena, D.; Armspach, D.; Egloff, C.;
Jouffroy, M.; Matt, D.; Toupet, L. Chem. – Eur. J. 2011, 17, 3911–3921.
doi:10.1002/chem.201002541
5. Wang, B.; Zaborova, E.; Guieu, S.; Petrillo, M.; Guitet, M.; Blériot, Y.;
Ménand, M.; Zhang, Y.; Sollogoub, M. Nat. Commun. 2015, 5,
No. 5354. doi:10.1038/ncomms6354
6A,6B,6D-Tri-O-trityl-α-CD (ABD-isomer): 13C NMR
(DMSO-d6) δ 144.11, 143.79, 128.29, 128.15, 128.09, 127.54,
127.45, 127.38, 126.62, 102.25, 101.97, 101.82, 101.68, 101.46,
101.42, 85.92, 85.86, 85.69, 82.53, 82.44, 81.93, 81.38,
80.85, 80.67, 73.39, 73.07, 72.92, 72.83, 72.60, 72.38,
72.09, 72.01, 71.96, 71.89, 70.91, 70.83, 70.58, 69.76, 63.45,
62.97, 62.58, 59.99, 59.02, 58.97 ppm; HRMS–ESI) (m/z):
[M + Na]+ calcd for C93H102O30Na+, 1721.6345; found,
1721.6067.
6. Cramer, F.; Mackensen, G.; Sensse, K. Chem. Ber. 1969, 102,
494–508. doi:10.1002/cber.19691020217
7. Melton, L. D.; Slessor, K. N. Carbohydr. Res. 1971, 18, 29–37.
doi:10.1016/S0008-6215(00)80256-6
8. Bergeron, R.; Machida, Y.; Bloch, K. J. Biol. Chem. 1975, 250,
1223–1230.
9. Boger, J.; Brenner, D. G.; Knowles, J. R. J. Am. Chem. Soc. 1979, 101,
7630–7631. doi:10.1021/ja00519a035
10.Eshima, K.; Mantsushita, Y.-i.; Hasegawa, E.; Nishida, H.; Tsuchida, E.
Chem. Lett. 1989, 18, 381–384. doi:10.1246/cl.1989.381
11.Coleman, A. W.; Ling, C.-C.; Miocque, M. Angew. Chem., Int. Ed. Engl.
1992, 31, 1381–1383. doi:10.1002/anie.199213811
12.Ling, C.-C.; Coleman, A. W.; Miocque, M. Carbohydr. Res. 1992, 223,
287–291. doi:10.1016/0008-6215(92)80026-W
6A,6B,6E-Tri-O-trityl-α-CD (ABE-isomer): 13C NMR
(DMSO-d6) δ 144.25, 143.69, 143.56, 128.28, 128.15,
127.96, 127.63, 127.42, 127.31, 126.68, 126.62, 126.53,
102.27, 102.22, 102.13, 101.89, 101.33, 101.08, 86.02,
85.95, 85.52, 83.51, 82.85, 81.63, 80.86, 80.68, 80.59,
73.42, 73.30, 72.99, 72.94, 72.73, 72.36, 72.29, 72.16,
72.05, 71.97, 71.86, 71.77, 71.27, 70.38, 70.35, 63.91, 63.13,
62.90, 59.73, 59.38, 58.58 ppm; HRMS–ESI (m/z):
[M + Na]+ calcd for C93H102O30Na+, 1721.6345; found,
1721.6067.
13.Tanimoto, T.; Tanaka, M.; Yuno, T.; Koizumi, K. Carbohydr. Res. 1992,
223, 1–10. doi:10.1016/0008-6215(92)80001-H
14.Tanimoto, T.; Sakaki, T.; Koizumi, K. Chem. Pharm. Bull. 1993, 41,
866–869. doi:10.1248/cpb.41.866
15.Tanimoto, T.; Ikuta, A.; Koizumi, K.; Kimata, K. J. Chromatogr. A 1998,
825, 195–199. doi:10.1016/S0021-9673(98)00712-2
16.Armspach, D.; Matt, D. Carbohydr. Res. 1998, 310, 129–133.
doi:10.1016/S0008-6215(98)00139-6
17.Khan, A. R.; Forgo, P.; Stine, K. J.; D’Souza, V. T. Chem. Rev. 1998,
98, 1977–1996. doi:10.1021/cr970012b
6A,6C,6E-Tri-O-trityl-α-CD (ACE-isomer): 13C NMR
(DMSO-d6) δ 143.98, 128.29, 127.54, 126.68, 102.23,
101.61, 85.97, 82.69, 80.89, 73.21, 72.81, 72.16, 72.06,
71.99, 70.53, 62.85, 59.14 ppm; HRMS–ESI (m/z):
[M + Na]+ calcd for C93H102O30Na+, 1721.6345; found,
1721.6067.
18.Ward, S.; Zhang, P.; Ling, C.-C. Carbohydr. Res. 2009, 344, 808–814.
doi:10.1016/j.carres.2009.02.005
19.Zhang, P.; Wang, A.; Cui, L.; Ling, C.-C. Org. Lett. 2012, 14,
1612–1615. doi:10.1021/ol300358u
20.Fujita, K.; Yamamura, H.; Matsunaga, A.; Imoto, T.; Mihashi, K.;
Fujioka, T. J. Am. Chem. Soc. 1986, 108, 4509–4513.
doi:10.1021/ja00275a042
21.Matsui, Y.; Fujie, M.; Sakate, H. Bull. Chem. Soc. Jpn. 1988, 61,
3409–3415. doi:10.1246/bcsj.61.3409
Supporting Information
22.Yamamura, H.; Nagaoka, H.; Saito, K.; Kawai, M.; Butsugan, Y.;
Nakajima, T.; Fujita, K. J. Org. Chem. 1993, 58, 2936–2937.
doi:10.1021/jo00063a005
Supporting Information File 1
1H NMR spectra of mono-, di-, and tri-O-trityl-α-CD,
together 2D COSY and TOCSY spectra of the AD-isomer.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-11-168-S1.pdf]
23.Yoshikiyo, K.; Shinjo, M.; Matsui, Y.; Yamamoto, T. Carbohydr. Res.
2015, 401, 58–63. doi:10.1016/j.carres.2014.10.027
1539

Beilstein J. Org. Chem. 2015, 11, 1530–1540.
License and Terms
This is an Open Access article under the terms of the
Creative Commons Attribution License
(http://creativecommons.org/licenses/by/2.0), which
permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
The license is subject to the Beilstein Journal of Organic
Chemistry terms and conditions:
(http://www.beilstein-journals.org/bjoc)
The definitive version of this article is the electronic one
which can be found at:
doi:10.3762/bjoc.11.168
1540