Using antiaromaticity to illuminate aromaticity during a research career with undergraduates.

Antiaromatic species tend to be among the least well-studied and understood group in organic chemistry, primarily because their anticipated instability dissuaded most chemists from exploring their behavior. A research project that was intended to form three-dimensional aromatic dications resulted instead in a set of antiaromatic dications from oxidation of fluorenylidene derivatives. These dications can be modified in ways that help illuminate factors that affect both antiaromaticity and aromaticity. The characterization of these species, as well as antiaromatic dianions, through magnetic, energetic, and structural properties is described along with the relationships between these properties. Because this work represents contributions almost exclusively from undergraduate researchers, and because many readers of the Journal may not have a great deal of experience in this environment, I also include some thoughts about the opportunities and challenges of undergraduate research.

Antiaromatic dianions: dianions of dixanthylidene by reduction and attempted excited-state deprotonation.

Reduction of dixanthylidene with potassium or lithium resulted in formation of the antiaromatic dianion in high yield. Attempts to form the dianion by excited-state deprotonation of dixanthene with n-butyllithium/TMEDA resulted in formation of the tetraanion from deprotonation ortho to the oxygen. Orientation of the sp(3) hydrogens presumably allows preferential deprotonation of the xanthene rings.

Magic acid free generation of antiaromatic dications at room temperature.

A new method for the generation of dicationic species via ionization of diols is described. The method makes use of milder reagents at room temperatures, an advantage over use of Magic Acid at -78 °C. A series of mono- and dications were synthesized successfully, including previously unattainable species.

Reduction of benzylidene dibenzo[a,d]cycloheptenes: over-reduction of antiaromatic dianions to aromatic tetraanions.

The antiaromaticity of a series of dianions of p-substituted benzylidene dibenzo[a,d]cycloheptenes was examined through calculated measures of antiaromaticity. The nucleus-independent chemical shifts (NICS) and magnetic susceptibility exaltation both showed substantial antiaromatic character in the benzannulated tropylium anion. When the antiaromaticity was normalized for the area of the ring, these tropylium anions were shown to be among the most antiaromatic anions in the chemical literature. Attempts to make the dianion through reduction with lithium or potassium gave the tetraanion as the only species observable in the (1)H NMR spectrum. Quench of the reaction mixture with trimethylsilyl chloride or D(2)O confirmed the presence of the tetraanion, but only as a small portion of the reaction mixture, with the major product being unreacted starting material. The failure to observe starting material was attributed to similarities in the structures of the starting material and anion radical (first reduction), allowing rapid electron transfer between them. The inability to see the dianion (second reduction) could be the result of the very small HOMO-LUMO gap anticipated for highly antiaromatic species, which would allow access to diradical species. The magnitude of the HOMO-LUMO gap was determined by the difference between the HOMO and LUMO energies from geometry optimization and the lowest energy transition from TD-DFT calculations. The HOMO-LUMO gap for the benzylidene dibenzocycloheptatriene dianions was shown to be much smaller than the HOMO-LUMO gap of species for which (1)H NMR spectra had been observed.

Dications of benzylidenefluorene and diphenylmethylidene fluorene: the relationship between magnetic and energetic measures of antiaromaticity.

Oxidation of m- and p-substituted benzylidene fluorenes to antiaromatic dications was attempted by electrochemical and chemical means. Electrochemical oxidation to dications was successful for benzylidene fluorenes with p-methoxy, p-methyl, p-fluoro, and unsubstituted phenyl rings in the 3-position; attempts to oxidize the m-substituted derivatives via electrochemistry were unsuccessful. Chemical oxidation with SbF(5)/SO(2)ClF gave the dication of 9-[(4-methoxyphenyl)methylene]-9H-fluorene cleanly; oxidation of all other substituted benzylidene fluorenes resulted in mixtures of products. The excellent linear relationship between the chemical shifts calculated by the GIAO method and the experimental shifts for the p-methoxy-substituted benzylidene fluorene dication suggests that the calculations satisfactorily reflect the magnetic properties of this dication and potentially those of the other dications studied. The redox potentials from electrochemical oxidation, a measure of the stability of the dications, showed a good linear relationship with another measure of stability, the calculated difference in energy between each dication and its neutral precursor. The dications of benzylidene fluorenes were less stable than the dications of diphenylmethylidene fluorenes; within each type of compound, dications with p-substituted phenyl rings were more stable than dications with m-substituted phenyl rings and dications with phenyl rings substituted with electron-donating groups were more stable than dications with phenyl rings substituted with electron-withdrawing groups. The antiaromaticity of the fluorenyl system was assessed through the nucleus-independent chemical shift (NICS) that was also calculated by the GIAO method. The plot of the NICS values per square area versus the calculated energy difference for the dications showed a moderate degree of linearity; the plot of NICS values per square area versus the oxidation potentials was less linear. Thus, a suggestive, but not conclusive, relationship between magnetic and energetic measures of antiaromaticity was observed.

Dications of 3-phenyl-indenylidene dibenzo[a.d]cycloheptene: the role of charge in the antiaromaticity of cationic systems.

Dications of 9-(3-phenyl-1H-inden-1-ylidene)-5H-dibenzo[a,d]cycloheptene, 5(2+), were prepared by oxidation with SbF(5) in SO(2)ClF, and their magnetic behavior was compared to dications of 9-(3-phenyl-1H-inden-1-ylidene)-9H-fluorene, 2(2+). The good correlation between the experimental (1)H NMR shifts for the dications that were oxidized cleanly and the chemical shifts calculated by the GAIO method supported the use of the nucleus independent chemical shifts, NICS, to evaluate the antiaromaticity of the indenyl systems of 2(2+)/5(2+) and their unsubstituted parent compounds, 6(2+) and 7(2+), as well as the antiaromaticity of the fluorenyl system of 2(2+)/7(2+) and the aromaticity of the dibenzotropylium system of 5(2+)/6(2+). Antiaromaticity was shown to be directly related to the amount of charge in the antiaromatic systems, with the antiaromatic systems more responsive to changes in the calculated NBO charge than the aromatic systems. The antiaromaticity was also shown to be directly related to the amount of delocalization in the ring system. The aromaticity of the dibenzotropylium system was much less responsive to changes in the amount of charge in the tropylium system, because the aromatic system was much more completely delocalized. Thus, antiaromatic species are more sensitive probes of delocalization than aromatic ones.

A pilot study of dose-dense adjuvant paclitaxel without growth factor support for women with early breast carcinoma.

PURPOSE: Granulocyte-colony stimulating factor (G-CSF) was used in CALGB 9741 to support dose-dense sequential chemotherapy with doxorubicin and cyclophosphamide (AC) followed by paclitaxel (P) (Citron et al. J Clin Oncol 21:1431-1439, 2003). However, myelosuppression is not known to be dose or schedule limiting for paclitaxel. We therefore conducted this trial to determine the need for routine G-CSF, using the pegylated product (pG-CSF), support during the paclitaxel component of dose-dense sequential chemotherapy in women with early stage breast carcinoma (BC). PATIENTS AND METHODS: Eligible patients received dose-dense chemotherapy consisting of four cycles of AC followed by four cycles of P at two week intervals. pG-CSF (Neulasta) was administered after each of four cycles of AC but was held after P. Planned enrollment was 59 pts. RESULTS: Of the first 15 patients, nine completed therapy without delays due to neutropenia but 6 (40%) did not, leading to implementation of the pre-specified early termination rule. Overall, 85% of P doses were successfully delivered on time. The mean treatment delay for the entire group due to neutropenia was 0.75 days. There was no significant correlation between neutropenia and prior WBC, ANC, or concurrent treatment with trastuzumab. Pts with neutropenia tended to be younger (Mean age 43.5) and have a lower BSA (1.65 m(2)). There were no febrile episodes due to omission of pG-CSF. CONCLUSION: When paclitaxel is administered in a dose-dense fashion without growth factor support brief treatment delays are common. Further study is needed to identify the minimal pG-CSF administration that will avoid treatment delays.

Antiaromatic spacer-bridged bisfluorenyl dications generated by superacid induced ionization.

Derivatives of the dication of tetrabenzo[5.5]fulvalene were prepared with phenyl and ethynyl spacers through ionization of the appropriate bis-methylethers. The antiaromaticity shown by the parent dication was demonstrated for these dications with spacers, although it was attenuated by the presence of the spacer. It was substantially greater than that of fluorenyl monocations with similar substituents. Antiaromaticity was evaluated through comparison of (1)H NMR shifts with those of acyclic analogues, through nucleus independent chemical shifts, and through magnetic susceptibility exaltation. Although the fluorenyl systems are separated by spacers, the antiaromaticity of one system is affected by the other remote fluorenyl system. An explanation for this interaction may lie in the ability of a remote cationic substituent to attenuate delocalization in the spacer. The use of spacers is designed to prevent side reactions in less stable antiaromatic dications, allowing exploration of a number of species that have previously been inaccessible.

Dianion and dication of tetrabenzo[5.7]fulvalene. Greater antiaromaticity than aromaticity in comparable systems.

The dianion, 5(2-), and dication, 5(2+), of tetrabenzo[5.7]fulvalene represent an aromaticity/antiaromaticity continuum in which the fluorenyl system changes from aromatic in 5(2-) to antiaromatic in 5(2+). Conversely, the antiaromatic dibenzotropylium system of 5(2-) becomes an aromatic system in 5(2+), allowing an examination of aromaticity/antiaromaticity within the same carbon framework. Dianion 5(2-) was prepared and characterized by (1)H NMR spectroscopy. The fluorenyl system of 5(2-) showed the downfield shifts expected for an aromatic system, while the dibenzotropylium system showed the paratropic shifts expected for an antiaromatic system. The conclusions from (1)H NMR spectroscopy were supported by NICS(1) zz calculations for each system. Comparison of the (1)H NMR spectrum and NICS(1) zz of 5(2-) with those of 5(2+) supported the assignments of aromaticity/antiaromaticity for each system. Aromaticity/antiaromaticity were further examined through comparison of the degree of bond length alternation, which showed that the bond length alternation was slightly greater for the antiaromatic ring systems than for the aromatic systems. However, when structures of 5(2-) and 5(2+) with no bond length alternation were examined, there was a dramatic increase in the degree of antiaromaticity for the antiaromatic ring systems as evaluated through NICS. This result suggests that a decrease in bond length alternation results in an increase in antiaromaticity as well as an increase in aromaticity. The magnitude of the antiaromaticity of the fluorenyl system in 5(2+) was greater than the magnitude of the aromaticity in the fluorenyl system of 5(2-), with similar effects shown by the analogous tropylium systems. This is consistent with the behavior of the antiaromatic dication of tetrabenzo[5.5]fulvalene, compared to that of its aromatic dianion, and also with the behavior of the cyclopentadienyl cation/anion and tropylium cation/anion.

Prolonged dose-dense epirubicin and cyclophosphamide followed by paclitaxel in breast cancer is feasible.

PURPOSE: We conducted a pilot study of dose-dense epirubicin/cyclophosphamide (EC) x 6 --> paclitaxel (P) x 6 with pegfilgrastim. A previous dose-dense trial of FEC (5-fluorouracil [5-FU]/EC) x 6 with filgrastim --> by weekly paclitaxel alternating with docetaxel x 18 was not feasible because of pneumonitis (with dose-dense FEC) and pericardial/pleural effusion (taxane phase). Dose-dense EC (without the 5-FU) is not associated with pneumonitis, and dose-dense paclitaxel (alone) is feasible. Primary objective was feasibility. PATIENTS AND METHODS: Patients with resectable breast cancer were enrolled, regardless of surgery status, tumor size, or nodal status. Treatment regimen consisted of every-2-week EC (100/600 mg/m2) x 6 --> by 2-weekly P (175 mg/m2) x 6 with pegfilgrastim 6 mg on day 2. RESULTS: Between November 2004 and May 2005, 38 patients were enrolled. The median age was 47 years (range, 30-72 years); 33 of 38 (87%) were treated in the adjuvant setting and 27 of 33 (81%) had involved nodes (range, 1-46); 5 of 38 (13%) were treated pre-operatively; 33 of 38 (87%) completed all chemotherapy as planned; the remaining patients (13%) had treatment modifications for toxicity. Febrile neutropenia occurred in 6 of 38 patients (16 %) and only during EC. There were 12 hospitalizations in 9 of 38 patients (24%) enrolled. CONCLUSION: Dose-dense every-2-week EC x 6 --> P x 6 with pegfilgrastim is feasible based on our prospective definition.

The effect of electrolyte imbalance on weaning from cardiopulmonary bypass: an experimental study.

An imbalance in electrolyte concentration during separation from cardiopulmonary bypass (CPB) may lead to a disruption in excitation-contraction coupling resulting in a failure to wean. The etiology of myocardial dysfunction is multifactorial, and includes alterations in acid-base balance, glucose metabolism, and cellular function. The purpose of this study was to assess the effect of hyperkalemia on myocardial function during separation from CPB. A porcine model (n = 5) of hypothermic (32 degrees C) CPB was used where hyperkalemia [K+ (6.5 +/- 1.0)] was created before weaning. A 3-minute weaning process was initiated once normothermia was achieved. Mixed venous and arterial samples were obtained during CPB, weaning, and 10 minutes postbypass. Samples were assayed for [K+], [Ca++], glucose, pH, CPK-MB, and lactic acid levels. Hyperkalemia resulted in the generation of severe arrhythmias in all animals. During the immediate prewean period, there was a significant correlation between venous [K+] and pH (p < .01, r2 =.891). Arterial pH did not change during the weaning or post-CPB period, while venous pH declined significantly throughout the same period (7.35 +/- 0.75 to 7.20 +/- 0.17, p < .05). No other measured variables correlated with hyperkalemia. In summary, hyperkalemia caused a significant decline in venous pH evidenced in the early separation period, but had no effect on other variables. Therefore, measurement of venous pH may be an early marker indicating myocardial dysfunction and dysrhythmia.

Expanding perfusion services through mobile point-of-care coagulation monitoring.

Current trends in cardiac surgery have challenged perfusionists to seek diversification of services. Point-of-care coagulation (POCC) monitoring represents a desirable area of perfusion service expansion. The purpose of the study was to create a series of hemostatic conditions to assess the functionality of POCC monitors to identify specific coagulopathies with identifiable profiles for algorithm development. Fresh (< 4 h) bovine blood, anticoagulated with anticoagulant citrate dextrose, was adjusted to a hematocrit of 30.0 +/- 2.0%. Hypofibrinogenemia < or = 90 mg/dL), thrombocytopenia (< or = 70,000/mm3), platelet dysfunction (850 microg/mL of nitroglycerin/mL of blood) and hyperfibrinolysis (0.40 units of urokinase/mL of blood) were created. Five POCC devices were used to evaluate activated clotting time, thrombin time, fibrinogen, platelet function, prothrombin time, activated partial thromboplastin time and thromboelastograph. Results are reported as percentage change from control for each test (abtract table). [table: see text] Each test performed showed specificity and sensitivity for certain coagulopathies, however variability amongst monitors was encountered. In conclusion, the development of a mobile cart incorporating POCC monitors with knowledge of specific coagulopathic conditions may expand perfusion service.

The effects of ultrafiltration on e-aminocaproic acid: an in vitro analysis.

Blood conservation strategies have become a standard of practice in cardiac surgery, with the use of antifibrinolytic agents and ultrafiltration two popular techniques. The purpose of this study was to evaluate the effects of continuous ultrafiltration on e-aminocaproic acid (EACA) utilizing functional coagulation analysis. A fibrinolytic assay was developed to detect EACA using the thromboelastograph (TEG) and urokinase (0.138 units 0.360 mL(-1)). Fresh bovine blood (23 +/- 1% hematocrit) was pumped (100 mL min(-1)) through an ultrafiltrator (HPH 400) at 37 degrees C with a transmembrane pressure of 280 mmHg. EACA (0.065 mg mL(-1)) was circulated for 10 minutes before initiating ultrafiltration. Samples (pre- and postultrafiltrator) were obtained at baseline, 5, and 10 min of ultrafiltration and analyzed via the fibrinolytic assay for EACA determination. TEG profiles significantly decreased from concentrations of 0.065 mg to 0.0325 mg of EACA mL(-1) blood (maximum amplitude MA, 75.4 +/- 4.0 versus 63.3 +/- 2.9, p < .05, TEG index 5.4 +/- 0.7 versus 4.0 +/- 0.3, p < .05). Fibrinolysis at 30 min increased as EACA concentrations declined (0.065 mg, 0% versus 0.032 mg, 16.4 +/- 2.8%, p < .05). During ultrafiltration the MA increased significantly from baseline to 10 min postultrafiltrator (68.2 +/- 3.0 versus 75.8 +/- 10.0, p < .05) and from 5 min pre- to 10 min postultrafiltrator (69.7 +/- 4.2 versus 75.8 +/- 10.0, p < .05). The TEG index showed no significant change, and no fibrinolysis was detected at 30 min from any datapoint during ultrafiltration. In conclusion, this study demonstrates that the antifibrinolytic properties of EACA are maintained during ultrafiltration with a 25% reduction in total circulating volume.

The effect of controlled aprotinin administration through cardiotomy suction during cardiopulmonary bypass.

Cardiotomy suction enhances inflammation and fibrinolysis during cardiopulmonary bypass (CPB). Aprotinin has been shown to reduce the generalized inflammatory insults associated with CPB. The purpose of this study was to evaluate the effect of Aprotinin administration through cardiotomy suction on the inflammatory and fibrinolytic responses during CPB. A pig model of CPB was utilized including 8 animals divided into control and treatment groups. In the treatment group, Aprotinin was infused into the cardiotomy suction (3000 KIU/min), while the same volume of saline was infused in the control group. D-dimer, platelet count, and IL-8 level were analyzed from systemic and cardiotomy suction. It was found that Aprotinin significantly suppressed the increase in D-dimer levels in the systemic (476.3 +/- 341.2 vs. 1218.8 +/- 281.3 ng/ml, p < 0.05) and the cardiotomy suction (565.0 +/- 192.5 vs. 1875.0 +/- 125.0 ng/ml, p < 0.05). Platelet count fell in both groups during CPB, although the reduction was greater in the control (13.1 +/- 5.1 vs. 37.9 +/- 13.8%, p < 0.05). In addition, IL-8 level in the suction solution was significantly lower in the Aprotinin group (56.5 +/- 18.0 vs. 136.3 +/- 14.8 pg/ml, p < 0.05). In conclusion, this study suggested that Aprotinin treatment of the cardiotomy solution might be an effective way of reducing fibrinolysis, platelet reduction, and inflammation associated with CPB.

Effects of increasing FiO2 on venous saturation during cardiopulmonary bypass in the swine model.

Adequacy of perfusion during cardiopulmonary bypass (CPB) is dependent on nutrient delivery and waste removal from the tissue. A recent study showed that over 75% of cardiopulmonary bypass procedures are completed using continuous venous saturation (SvO2) monitoring. The purpose of this study was to determine the effect of changing FiO2concentration on SvO2. A total of eight mixed gender 45-kg swine were placed on CPB under moderate hypothermic conditions. Animals were divided evenly into two groups: Experimental, where FiO2 was increased to 100% and blood flow decreased to an SvO2 level of prechange in FiO2, and Control, where the same condition was created except no change in blood flow. Variables measured include hemodynamic, blood gas, intramyocardial pH, and lactic acid concentrations. In the experimental group, percentage change of blood flow was decreased from baseline 28.4% +/- 12.5% (p < .005) as well as percentage change of oxygen delivery 23.9% +/- 14.7% (p < .005). Systemic venous saturation percentage change was increased in both the experimental 14.4% +/- 6.8% (p < .05) and control 11.2% +/- 7.1% (p < .05) groups. Jugular venous saturation percentage change was decreased in the experimental group 7.8% +/- 6.34% (p < .02), but not in the control animals. Myocardial venous saturation percentage change decreased in the experimental group to 3.73% +/- 8.34% (p < .004). Experimental manipulation, however, did not significantly change jugular lactic acid concentrations or intramyocardial pH values. In conclusion, these results suggest that decreased blood flow adjusting for increased SvO2 associated with high PaO2 did not result in significant reduction of adequacy of perfusion markers for organs studied.

Relationship of charge to antiaromaticity in bis-fluorenyl dications and fluorenyl monocations: experimental support for theoretical calculations.

The antiaromaticity of fluorenyl cations is dependent on the magnitude of the charge of the system. Theoretical assessments of antiaromaticity and charge were supported by experimental NMR chemical shifts. Delocalization was related to antiaromaticity, and evaluated through the standard deviation of the charges on carbons of the fluorenyl systems.

Dose dense cyclophosphamide, methotrexate, fluorouracil is feasible at 14-day intervals: a pilot study of every-14-day dosing as adjuvant therapy for breast cancer.

PURPOSE: Cyclophosphamide/methotrexate/fluorouracil (CMF) is a proven adjuvant option for patients with early-stage breast cancer. Randomized trials with other regimens demonstrate that dose-dense (DD) scheduling can offer greater efficacy. We investigated the feasibility of administering CMF using a DD schedule. PATIENTS AND METHODS: Thirty-eight patients with early-stage breast cancer were accrued from March 2008 through June 2008. They were treated every 14 days with C 600, M 40, F 600 (all mg/m2) with PEG-filgrastim (Neulasta®) support on day 2 of each cycle. The primary endpoint was tolerability using a Simon's 2-stage optimal design. The design would effectively discriminate between true tolerability (as protocol-defined) rates of ≤ 60% and ≥ 80%. RESULTS: The median age was 52-years-old (range, 38-78 years of age). Twenty-nine of the 38 patients completed 8 cycles of CMF at 14-day intervals. CONCLUSION: Dose-dense adjuvant CMF is tolerable and feasible at 14-day intervals with PEG-filgrastim support.

Antiaromaticity in distal bisfluorenyl dications separated by multiple discrete spacer units.

The effect of spacers on the antiaromaticity of bisfluorenyl dications was examined. For systems such as 4a-c in which extensive delocalization of the positive charge through the pi-system is not possible, a relationship based primarily on localized hyperconjugation as well as the distance between the fluorenyl systems and their antiaromaticity was demonstrated. Dications 2a-c and 3a-c also show the relationship, but it is further modulated by delocalization through the pi-system. Calculated assessment of antiaromaticity was supported by experimental shifts for 2a,b and 3a-c.

The safety of dose-dense doxorubicin and cyclophosphamide followed by paclitaxel with trastuzumab in HER-2/neu overexpressed/amplified breast cancer.

PURPOSE: Dose-dense (dd) doxorubicin and cyclophosphamide (AC) followed by paclitaxel (P) is superior to every 3-weekly AC followed by P. Given the demonstrated cardiac safety for trastuzumab (T) with conventionally scheduled AC followed by P, we tested the safety of dd AC followed by P with T. The primary end point was cardiac safety, and the secondary end points were time to recurrence and overall survival. METHODS: Patients with HER-2/neu immunohistochemistry (IHC) 3+ or fluorescent in situ hybridization (FISH)-amplified breast cancer and baseline left ventricular ejection fraction (LVEF) of >or= 55% were enrolled, regardless of tumor size or nodal status. Treatment consisted of AC (60/600 mg/m(2)) x 4 followed by P (175 mg/m(2)) x 4 every 2-weekly with pegfilgrastim (6 mg on day 2) + T x1 year. LVEF by radionuclide scan was obtained at baseline, at months 2, 6, 9, and 18. RESULTS: From January 2005 to November 2005, 70 patients were enrolled. The median age was 49 years (range, 27 to 72 years); median LVEF at baseline was 68% (range, 55% to 81%). At month 2 in 70 of 70 patients, the median LVEF was 67% (range, 58% to 79%); at month 6 in 67 of 70 patients, it was 66% (range, 52% to 75%); at month 9 in 68 of 70 patients, it was 65% (range, 50% to 75%); and at month 18 in 48 of 70 patients, it was 66% (range, 57% to 75%). As of December 1, 2007, the median follow-up was 28 months (range, 25 to 35 months). One patient (1%) experienced congestive heart failure (CHF). There were no cardiac deaths. CONCLUSION: Dose-dense AC followed by P/T followed by T is feasible and is not likely to increase the incidence of cardiac events compared to established regimens.