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The cryptophycins, isolated from cyanobacteria, are a family of macrocyclic molecules. Researchers have studied the biological activity of these compounds and found that many of them are active against multi-drug-resistant tumor cells.Cryptophycin-52, an analogue of the natural cryptophycins, has been tested in clinical trials for its efficacy against cancer cells, but the studies were suspended due to neurotoxic side effects. Nevertheless, the synthesis of similar analogues continues to be of interest in cancer research. A key step in the synthesis of cryptophycin-52 is the stereospecific formation of an epoxide from an alkene and oxone (Figure 1) , which can be facilitated by the Shi catalyst. The Shi catalyst (Figure 2) is derived from the carbohydrate D-fructose and is known among organic chemists for its ability to form epoxides in hydrocarbons in a stereospecific manner.
Figure 1 Shi epoxidation of compound 1
Figure 2 Structure of the Shi catalystThe epoxidation of compound 1 was monitored by thin-layer chromatography (TLC) . When the reaction was completed, high-performance liquid chromatography (HPLC) was used to analyze the epoxide product. A chiral column that had an affinity for the desired epoxide was used. A standard of the desired epoxide was obtained to optimize the conditions and determine the retention time of the epoxide. The HPLC chromatogram of the epoxide standard is shown in Figure 3.
Figure 3 HPLC of epoxide standard
Adapted from Weiß C, Bogner T, Sammet B, Sewald N. Total synthesis and biological evaluation of fluorinated cryptophycins. Beilstein J Org Chem. 2012.
-After isolation of compound 1, an infrared spectrum was obtained. The spectrum gives all of the following information EXCEPT:

Question

Passage
The cryptophycins, isolated from cyanobacteria, are a family of macrocyclic molecules. Researchers have studied the biological activity of these compounds and found that many of them are active against multi-drug-resistant tumor cells.Cryptophycin-52, an analogue of the natural cryptophycins, has been tested in clinical trials for its efficacy against cancer cells, but the studies were suspended due to neurotoxic side effects. Nevertheless, the synthesis of similar analogues continues to be of interest in cancer research. A key step in the synthesis of cryptophycin-52 is the stereospecific formation of an epoxide from an alkene and oxone (Figure 1) , which can be facilitated by the Shi catalyst. The Shi catalyst (Figure 2) is derived from the carbohydrate D-fructose and is known among organic chemists for its ability to form epoxides in hydrocarbons in a stereospecific manner.

Figure 1 Shi epoxidation of compound 1

Figure 2 Structure of the Shi catalystThe epoxidation of compound 1 was monitored by thin-layer chromatography (TLC) . When the reaction was completed, high-performance liquid chromatography (HPLC) was used to analyze the epoxide product. A chiral column that had an affinity for the desired epoxide was used. A standard of the desired epoxide was obtained to optimize the conditions and determine the retention time of the epoxide. The HPLC chromatogram of the epoxide standard is shown in Figure 3.

Figure 3 HPLC of epoxide standard
Adapted from Weiß C, Bogner T, Sammet B, Sewald N. Total synthesis and biological evaluation of fluorinated cryptophycins. Beilstein J Org Chem. 2012.
-After isolation of compound 1, an infrared spectrum was obtained. The spectrum gives all of the following information EXCEPT:

Quizplus · Accepted Answer

11ecba2d_1263_87d0_a3bf_09d489f44b63_MD0008_00 Infrared (IR) spectroscopy is a technique used to identify functional groups in a compound by analyzing the types of bonds present. The sample is irradiated with infrared light, which interacts with the bonds in the molecule. The amount of light absorbed is recorded by the detector, and the data collected is displayed on the IR spectrum as percent transmittance (y-axis) vs. wavenumber (x-axis). Transmittance is inversely related to absorbance (ie, if all the light is absorbed, there is 0% transmittance). The wavenumber (with units of cm⁻¹) is the infrared frequency and is defined as the inverse of the wavelength. Because the wavenumber is related to wavelength, it is also directly related to frequency by the equation: 11ecba2d_1263_87d1_a3bf_a1af24cf8804_MD0008_00 where f is the frequency, c is the speed of light, and λ is the wavelength. Therefore, IR spectroscopy measures absorbance at different frequencies (Choice C). Frequency is directly related to energy (Choice D). The energy needed to stretch a bond at a certain wavelength can be calculated using: 11ecba2d_1263_87d2_a3bf_b16232efd082_MD0008_00 where E is energy and h is Planck constant. IR radiation ranges from 700 nm to 1 mm, and causes bond stretching vibrations and rotations at different frequencies (Choice B). Functional groups absorb different amounts of energy depending on the type of bond present. Therefore, the intensity of the signals from bond-stretching vibrations and rotations at a certain frequency depends on the amount of energy absorbed. Spin-spin splitting of atoms is a phenomenon that occurs in nuclear magnetic resonance (NMR) spectroscopy. It revolves around how protons act in a magnetic field and the effect they have on the signals of neighboring protons. Educational objective: Infrared spectroscopy is a technique used to determine the functional groups present in a sample; the data collected are plotted as percent transmittance vs. wavenumber. The signals in the spectrum correspond to bond-stretching vibrations and rotations at a certain frequency, and the signal intensity is dependent on the amount of energy absorbed.

Passage The Cryptophycins, Isolated from Cyanobacteria, Are a Family of Macrocyclic