Louise Quelch
42935746
SCIE3001
14/8/13
Justification
Major changes were made in almost every section of the report. Adding a title which fully described
the paper, but was still able to be concise was very important. This is because it is the first thing that
the readers will see and will determine whether they will continue reading [1]. Usually read second,
an abstract that summarise the whole report while being able to stand on its own and hold the
reader’s attention it is vital [2]. Pointed out by both reviews, the introduction, had little to no
background or context. However, now there is crucial information such as detail about the different
anomers and the reaction mechanism. The introduction was structured with a broad start and
gradually got to the specific aims of the investigation [3]. The results were displayed logically from
most important to the justification in the discussion, 1H NMR, to least important, the yield. The
discussion had a lot of work done on the structure and the content. It was structured with
information that most supported the conclusions at the start, and as it went on the information
became more general [4]. The paragraph justifying the assignment of the hydrogens was removed.
For much of the audience this information would be irrelevant and it was not highly relevant in
coming to the conclusions. There was also many general improvements. One of these was catering
the paper for an audience with a minimal chemical background. This resulted in many ideas and
terms being defined and explained in depth. Another improvement was the visual appeal of the
figures and how they were integrated into the text. These improvements outlined and many others
demonstrate how the reviewed paper is more effective at communicating the science to the desired
audience.
References
[1] T. M. Annesley, Clinical Chemistry, 56:3, 257 -260
[2] T. M. Annesley, Clinical Chemistry, 56:4, 531 -524
[3] T. M. Annesley, Clinical Chemistry, 56:5, 708–713
[4] T. M. Annesley, Clinical Chemistry, 56:11, 1671–1674
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Louise Quelch
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Anomeric composition of D-glucose pentaacetate after
synthesis
Louise Quelch
Abstract
In the formation of ethers as part of a cyclic ring, a new chiral centre is formed. This causes two
anomers of the same molecule. α and β-D-glucose pentaacetate are an example of this. The aim of
this investigation was to synthesis D-glucose pentaacetate and determine the anomeric composition
of the purified product. This was achieved by reacting α-D-glucose with anhydrous sodium acetate
and purifying the precipitate. A 1H NMR was run on this product and melting point of 108.5 – 123.2
°C recorded. The 1H NMR was compared to 1H NMR spectrums of known α and β-D-glucose
pentaacetate samples (provided by The University of Queensland’s SCMB). From the comparison it
was clear that the product had aspects of both anomers. The intergrals of the peaks demonstrate
that there was significantly more of the β anomer present. Another way to identify the anomer is
through the differing coupling constants cause by dihydrogen interaction between the hydrogen
atoms on and adjacent to the anomeric carbon, either the β diaxial, 7 - 10 Hz, or α axial-equatorial, 2
– 6 Hz. The coupling constant determined was 10.88 Hz. While this does not fit directly into either
range it is clearly closer to the expected coupling constant for the β anomer. For these reasons it was
determined that the major product was the β anomer.
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Louise Quelch
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SCIE3001
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Introduction
Anomers have different chemical and physical properties, so it is vital to be able to determine
procedures to form each anomer. For example α-D-glucose pentaacetate (figure 2) has been shown
to induce insulin release in rate, however its anomer β-D-glucose pentaacetate (figure 1) did not.
This is just one situation where it is vital to be able to distinguish between the two anomers.[1]
Figure 1: β-D-glucose-pentaacetale
Figure 2: α-D-glucose pentaacetale
D-glucose pentaacetate (figures 1 and 2) is formed through the acetylation of α-D-glucose (figure 3).
Acetylation is the process of adding an acetyl group (R-COCH3) to a hydroxyl group (R-OH). In the
case of glucose there are 5 hydroxyl groups, which are all acetylated.
Figure 3: Acetylation of D-glucose; R is the alcohol groups on the glucose
α- D-glucose pentaacetate and β-D-glucose pentaacetate differ in the orientation of the functional
group on C-1 (position 1, figure 1) the α anomer has the group in the axial position (perpendicular to
the plane of the molecule), whereas the β anomer has the group in the equatorial position (in the
plane of the molecule). Which anomer forms depends on the direction that alcohol group and the
aldehyde interact to for a hemiacetal. Once the 6 membered ring is formed these anomers are
locked. Only through the opening and reclosing of the 6 membered ring, mutarotation [2], can Dglucose pentaacetate (and glucose) alteration between the α and β anomers.
The aim of this experiment was to synthesis glucose pentaacetate through the acetylation of α-Dglucose. Once synthesised and purified the 1H NMR was used to determine the anomeric
composition, ie whether the product was β-Glucose pentaacetate or α-Glucose pentaacetate.
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Louise Quelch
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SCIE3001
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Method
Formation of D-glucose pentaacetate:
α-D-glucose (5.0007 g, 0.027757 mol) was added to anhydrous sodium acetate (2.51 g, 0.0306 mol)
and refluxed for an hour with acetic anhydride (25 mL, 0.264 mol). The solution was added to
distilled ice water for 15 minutes. The solution was vacuum filtered and the precipitate collected.
This product was then recrystallised by dissolving in minimal boiling methanol and allowed to
crystallise again. The product was collected and rinsed with cold methanol.
1
H NMR Procedure:
The product (≈0.3 g) was dissolved in deuterochloroform (≈1 mL). A 1H NMR spectra (400 Hz) was
run on this solution.
Results
The 1H NMR results are displayed in table 1. The NMR shows 11 major peaks many of which have
been split into ‘sub-peaks’ due to influence of neighbouring hydrogens, this is described by the
multiplicity. Each peak can represent multiple hydrogens, this was determined by integration of the
major peak. Another conclusion of the NMR is the coupling constant. It is calculated by the
difference in chemical shift of the lowest and highest sub-peaks multiplied by the frequency (400
Hz). For raw data refer to Appendix 1.
Chemical shift –
average (ppm)
5.7146
5.2527
5.1285
No. of
Hydrogens
1
1
2
4.289
1
4.11125
1
3.83775
1
2.1141
2.0856
2.0325
2.0126
3
3
6
3
Multiplicity
Doublet
Triplet
Doublet of
triplets
Doublet of
doublets
Doublet of
doublets
Doublet of
doublets of
doublets
Singlet
Singlet
Singlet
Singlet
Coupling
constant (Hz)
10.88
24.88
27.84
Assignment
22.72
6
1
2
3,4
19.64
22.2
5
0
0
0
0
7
11
8 and 10
9
Table 1 - 1H NMR results (Note: assignment numbers refer to Figure 1)
The mass of the final purified glucose pentaacetate was 7.37 g, giving a yield of 68.0 % and a melting
point of 108.5 – 123.2 °C.
Discussion
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Louise Quelch
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In this study D-glucose pentaacetate was synthesised, it was determined that the resulting product
was a mixture of both the α and β anomers, with β-D-glucose pentaacetate being the predominant
species. This finding is supported by both the 1H NMR and the melting point range.
When compared to 1H NMR spectrums α-D-glucose pentaacetate and β-D-glucose pentaacetate (see
appendix 2and 3), provided by The University of Queensland’s SCMB, the spectrum of the product
could clearly been seen to align more strongly with that of the β anomer. One example of this is the
peak corresponding to the hydrogen attached to C-1 (position 1, figure 1). This hydrogen is the least
shielded by electrons, since there is a greater number of electron withdrawing oxygen atoms in close
proximity. This causes the peak to be lower field ie to have a higher chemical shift, which in the case
of the hydrogen on C-1 in the β anomer is approximately 5.7 ppm. However in the α anomer it is
around 6.3 ppm. When the product was tested, peaks at both 5.7 and 6.3 ppm were observed.
Appendix 1, page 6, shows this. From the relative integrals of these peaks it can be seen that the
amount of β anomer in the final product is significantly larger.
Another way to differentiate between the two anomers is the value of the coupling constant of in
the peak from the hydrogen bonded to C-1. As seen in figures 1 and 2, α-D-glucose pentaacetal and
β-D-glucose pentaacetal have the substituents in the equatorial and axial positions respectively. This
means that in the β anomer the Hydrogen in position 1 is axial. This causes diaxial interactions
between itself and the hydrogen in position 2. This causes coupling constants of 7 – 10 Hz.
Conversely the hydrogen in position 1 in the α isomer is equatorial causing equatorial-axial
interactions, resulting in coupling constants of 2 - 6 Hz. In table 1 it can be seen that the coupling
constant recorded is 10.88 Hz. While this value does not fit directly in the diaxial interactions range it
is significantly closer and therefore it can be concluded that the majority of the product is β-Dglucose pentaacetate.
More evidence to support the explaination of both anomer existing in the product it the recorded
melting range. The literature values for the melting points of β-Glucose pentaacetate and α-Glucose
pentaacetate are 131 – 132 °C[3] and 111 – 112 °C[4] respectively. The large range of the melting
point, 108.5 – 123.2 °C, can be attributed to the final product containing the α and β anomers. The
melting point recorded does not seem very reliable due to its low start point, compared to the
literature values of both anomers. One likely explaination is that the product was not completely
dry, ie still containing methanol, when the melting point was recorded.
As seen in inaccuracy of the melting point, this study has many possible ways in which it could be
improved. Another example of this is in the low yield of 68.0 %. One literature value for the yield of a
very similar procedure was 85 % [5]. The calculated yield was decrease due to loss of both products
and reactants throughout the reaction. Many reactants were lost through the reflux, as not all of the
solid was dissolved into solution. In situations where time is not limited it would improve the yield to
leave the mixture to reflux longer.
Conclusion
The major product produced was β-Glucose pentaacetate. This was determined through 1H NMR, by
using relationships with axial and equatorial hydrogens and analysing the 1H NMR of know sample of
α and β-D-Glucose pentaacetate. This investigation will be beneficial for any future need to
determine different procedures for the synthesis of the α or β- D-glucose pentaacetate.
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Louise Quelch
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SCIE3001
Appendix 1: Product 1H NMR
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SCIE3001
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Louise Quelch
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SCIE3001
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Louise Quelch
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Appendix 2: α-D-glucose pentaacetate 1H NMR
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Appendix 3: β-D-glucosepentaacetate 1H NMR
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References
[1] W. J. Malaisse, H. Jijakli, M. M. Kadiata, A. Sener, O. Kirk, Biochemical and Biophysical Research
Communications, 1997, 231, 435 - 436
[2] A. M. Silva, E. C. da Silva, C. O. da Silva, Carbohydrate Research, 2006, 341, 1029 – 1040
[3] U. Niedballa, H. Vorbruggen, J. Org. Chem., 1974, 39, 3659
[4] F. Dasgupta, P. P. Singh, H. C. Smvsrava, Ekevier Scientific Publishing Company, 1980, 80, 346
[5] A. Pulsipher and M. N. Yousaf Chem. Commun., 2011, 47, 523
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