Chemical Education Today
Reports from Other Journals
Research Advances Nitroxyl Verification; A Fast Check for Heroin; Acetic Acid Decreases Body Fat Buildup Angela G. King Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109;
[email protected] Novel Trap Detects Nitroxyl The pursuit of heart medications based on the compound nitroxyl (HNO) will be aided by a new research tool Wake Forest University scientists have developed that identifies unique chemical markers in biological systems. The results are welcome news for scientists working on new treatments for congestive heart failure (CHF). CHF is the inability of the heart to pump enough blood to supply the metabolic demands of the body. There are more than 5.7 million people in the United States with congestive heart failure, with more than 650,000 new diagnoses each year. The prognosis for patients with CHF remains poor, with a fiveyear mortality rate of 50% following diagnosis. More than $37 billion was spent in the United States in 2009 for the medical care of CHF patients. Acute decompensated heart failure (ADHF) is an acute exacerbation of CHF and the most common cause of hospitalization for patients over 65 years of age. Episodes of ADHF
HNO + Nuc H nitroxyl
HO HN Nuc H2N2O2
HNO + HNO
N2O + H2O
R3P = NH + R3P = O aza-ylide
HNO + 2R3P
Scheme I. HNO reacts as an electrophile with nucleophiles to form addition products. Image credit: B. King.
HNO + R3P
O NH HN O or R3H2P R3H2P
R3P HN O P R3
R3P = NH + R3P = O aza-ylide
Scheme II. Proposed mechanism of aza–ylide formation. Image credit: B. King.
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are marked by a severe diminution of cardiac function that typically results in fluid accumulation in the lungs (pulmonary edema) and consequent severe shortness of breath. There were 1.1 million hospitalizations for ADHF in the United States in 2006. The 30-day mortality rate is approximately 11%, and the one-year mortality rate is 34%. Treatment options for patients with ADHF remain limited. Current first-line treatments target the removal of excess fluid (diuresis) and vasodilation. To improve the hemodynamic profile of the heart and increase cardiac contractility, a physician may also administer an intravenous inotropic agent such as dobutamine or milrinone. Administration of these drugs often requires close monitoring in a hospital’s cardiac or intensive care unit because of the life-threatening safety risks associated with these drugs, including ventricular–atrial arrhythmias, hypotension, sudden cardiac death, and other potentially adverse long-term outcomes. Nitroxyl—the reduced, protonated form of the blood-vessel relaxing compound, nitric oxide (NO)—has demonstrated effects in animal models that are quite distinct from NO. In addition to providing peripheral vasodilation, nitroxyl has been shown to strengthen canine heartbeats and improve heart relaxation. However, research into nitroxyl’s potential benefits for humans has been slowed by the lack of specific detection methods. Researchers can produce nitroxyl from precursor chemicals under controlled conditions, but studying the molecule’s activity in cells is difficult because of its reactive nature. One problem is that HNO dimerizes to form H2N2O2, which then dehydrates to give N2O. For this reason, scientists are interested in trapping nitroxyl as it forms. A research team used triarylphosphines—compounds absent from normal cell biology—to produce a reaction that yields the identifying chemical markers, aza-ylides (Scheme I). In the presence of an electrophilic ester, the aza-ylide undergoes a Staudinger ligation to yield an amide with the nitrogen atom being derived from HNO. The amides can be detected by LC, GC–MS, or NMR; their detection verifies that nitroxyl was present in the system. The researchers proposed a mechanism for the reaction in which the phosphine reacts with HNO to yield a product either through P addition at N or O (Scheme II). Each of these initial addition products could exist as a three-membered ring species. Addition of a second phosphine gives the corresponding aza-ylide and phosphine oxide in equal proportions.
Journal of Chemical Education • Vol. 86 No. 11 November 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
Chemical Education Today
Reports from Other Journals S. Bruce King, who led the Wake Forest University research team and who has investigated nitrogen oxide compounds at Wake Forest since 1995, reflected that “I think this is a very powerful tool to help in the development of new drugs for congestive heart failure”. Although scientists have established that the human body naturally produces nitric oxide, natural production of nitroxyl is suspected yet has not been demonstrated. King said the new chemical markers could help answer that question, as well. Cardioxyl Pharmaceuticals, Inc., has developed a nitroxyl chemistry platform technology that serves as the foundation for the company’s drug discovery efforts. In 2003, Cardioxyl’s team members elucidated the cardiovascular effects of nitroxyl. Currently, Cardioxyl’s lead program focuses on the development of proprietary nitroxyl donors for the treatment of ADHF. Cardioxyl has recently announced the initiation of a Phase I/ IIa dose-escalation study of CXL-1020, the leading drug candidate. This study, which will evaluate the pharmacokinetics, safety, and tolerability of CXL-1020 in patients with chronic stable heart failure, has begun: the first patient was dosed in June 2009. The president and chief executive officer of Cardioxyl Pharmaceuticals, Chris Kroeger, reported, “CXL-1020 is a novel, first-in-class, small molecule nitroxyl (HNO) donor therapeutic drug candidate. Our initial studies in patients with stable heart failure are anticipated to provide a window through which we hope to better understand the potential utility of this novel agent in acute decompensated heart failure.” More Information 1. Reisz, J. A.; Klorig, E. B.; Wright, M. W.; King, S. B. Reductive Phosphine-Mediated Ligation of Nitroxyl (HNO). Org. Lett. 2009, 11, 2719–2721. 2. J. Chem. Educ. 2007, 84, 1668–1670 describes the trapping of an intermediate in the combustion of hydrogen. 3. Descriptions of research taking place in King’s lab can be found at http://www.wfu.edu/chem/faculty/BruceKingResearch.html/ (accessed Aug 2009). 4. A brief description of this research appeared in Chem. Eng. News 2009, 87 (24), 26. 5. More information on Cardioxyl Pharmaceuticals, Inc., is available online at http://www.cardioxyl.com/ (accessed Aug 2009).
Toward a Fast Test To Determine Street Heroin Purity Heroin is an opiate drug synthesized from morphine (Figure 1). Its highly addictive nature is associated with compulsive patterns of use. Scientists in Spain recently reported an advance toward a new method for determining the purity of heroin that could save lives by allowing investigators to quickly identify impure and more toxic forms of the drug being sold on the street. Unlike conventional tests such as gas chromatography and capillary electrophoresis, the new test does not destroy the original drug sample. In the study, Garrigues and colleagues pointed out that the purity of heroin can vary widely, as the heroin is often mixed
Figure 1. A sample of black tar heroin. Image credit: United States Drug Enforcement Agency.
with chalk, flour, or other “cutting agents”. Because heroin users do not know the exact purity of the drug, they are more at risk for overdose and even death. Conventional tests for determining the purity of street heroin involve destructive and time-consuming sample preparation, the scientists say. The research team studied 31 illicit drug samples from Spain that contained heroin in the range of 6–34% purity. The scientists tested the samples using diffuse reflectance nearinfrared spectroscopy (DR-NIR). DR-NIR involves shooting a beam of infrared light into a sample to determine its chemical composition based on the wavelength of light emitted. The scientists established a partial least-squares calibration model and compared the DR-NIR spectra of the illicit samples to that of pure heroin in the 850–2750 nm range. The method quickly and accurately determined the chemical content of the samples without any prior sample preparation, the scientists say. More Information 1. Moros, J.; Galipienso, N.; Vilches, R.; Garrigues, S.; de la Guardia, M. Nondestructive Direct Determination of Heroin in Seized Illicit Street Drugs by Diffuse Reflectance Near-Infrared Spectroscopy. Anal. Chem. 2008, 80, 7257–7265. 2. This Journal has previously published numerous undergraduate experiments involving diffuse reflectance spectroscopy, including J. Chem. Educ. 2003, 80, 672–675; 2002, 79, 1117–1118; and 1995, 72, 566. An overview of the technique is available in J. Chem. Educ. 1994, 71, A204. 3. The National Institute on Drug Abuse InfoFact Page on Heroin, http://www.nida.nih.gov/infofacts/heroin.html, offers additional scientific information on heroin’s effects and treatment options. 4. J. Chem. Educ. 2004, 81, 1362–1366 reviews the chemistry of alkaloids. Two other resources from this Journal investigate alkaloids: J. Chem. Educ. 2004, 81, 1366, Alkaloids: Strychnine, Codeine, Heroin, and Morphine ( JCE Featured Molecules); and J. Chem. Educ. 2000, 77, 993–998, Two Faces of Alkaloids.
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 11 November 2009 • Journal of Chemical Education
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Chemical Education Today
Reports from Other Journals New Evidence That Vinegar May Be Natural Fat Fighter Researchers in Japan are reporting that ordinary vinegar— a staple in salad dressings, pickles, and other foods—may live up to its folk-medicine reputation as a health promoter. New evidence suggests that the effects of acetic acid (AcOH) on fat oxidation can help prevent the accumulation of body fat and weight gain. Kondo and colleagues note in a new study that vinegar, in addition to its role as a seasoning, has been used as a folk medicine for a range of ills. Previous scientific research suggests that AcOH may help control blood pressure, blood-sugar levels, and fat accumulation. The proposed mechanism of action in decreasing fat buildup is that AcOH is metabolized to acetylCoA while producing adenosine monophosphate (AMP) in the liver. This leads to phosphorylation of 5′-AMP-activated protein kinase (AMPK), which downregulates genes involved in glucose metabolism or lipogenesis downstream of AMPK. The end result is suppression of body fat accumulation. The study shows that laboratory mice fed a high-fat diet and given AcOH in either low or high doses developed significantly less body fat (up to 10% less) than a control group of mice. However, comparison of the results from the low- and high-dose groups indicates that the effect reached a plateau with the low-dose group. Importantly, the new evidence supports the proposal that AcOH fights fat by turning on genes for fatty acid oxidation
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enzymes. The genes churn out proteins involved in breaking down fats, thus suppressing body fat accumulation. This new work reveals that AcOH upregulates the expression of genes for fatty acid oxidation enzymes and thermogenic proteins. Currently the research team is investigating the effects of AcOH on fatty acid oxidation in skeletal muscle. More Information 1. Kondo, T.; Kishi, M.; Fushimi, T.; Kaga. T. Acetic Acid Upregulates the Expression of Genes for Fatty Acid Oxidation Enzymes in Liver To Suppress Body Fat Accumulation. J. Agric. Food Chem. 2009, 57, 5982–5986. 2. This Journal has previously reported activities using vinegar to help students grasp stoichiometry. See J. Chem. Educ. 2008, 85, 1382–1384 and 1997, 74, 1328A–1328B. 3. Medscape General Medicine offers readers a comprehensive scientific review of past and present knowledge regarding the medicinal use of vinegar. See http://www.pubmedcentral.nih.gov/articlerender. fcgi?artid=1785201 (accessed Aug 2009). 4. J. Chem. Educ. 2001, 78, 721 provides safety information on glacial acetic acid.
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Journal of Chemical Education • Vol. 86 No. 11 November 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
