On the mechanism of quinone formation from the Bergman cyclization: some theoretical insights.
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Cyclization↗
Biomedical subjects
P M Warner
Publications and source records attributed to P M Warner.
Butalene and related compounds: aromatic or antiaromatic?
Density functional theory (DFT) has been used to study the first three members of the condensed cyclobutadienoid series, butalene (3), bicyclobutadienylene (12), and dicyclobutenobutalene (20). The first is planar and is judged "aromatic" by comparisons with suitable models using both energetic and magnetic criteria. The second is nonplanar, and not aromatic, but not so antiaromatic as cyclobutadiene (11). The third is slightly more antiaromatic and best viewed as a butalene fused to two cyclobutadiene rings; its properties are the sum of aromatic and antiaromatic components, like benzocyclobutadiene. Ring-opening transition states for both 3 and 12 have been located, and these are conrotatorily twisted. The ring-opening barrier for 12 is more than twice that for 3. Ring-opening of 20 involves ring inversion as the only barrier.
Journal Article↗
Electronic control of the Bergman cyclization: the remarkable role of vinyl substitution.
We report an ab initio study of the effect of vinyl substitution on the cycloaromatization of 3-ene-1,5-diynes (the Bergman cyclization). The majority of the calculations were conducted by using the BLYP version of Density Functional Theory, and higher level Brueckner orbital calculations were used for a few key compounds. In all, 46 enediynes, 44 cyclization transition states, 39 singlet p-benzynes, and 28 related triplet p-benzynes were studied, including simple vinyl-substituted and annulated examples. The data indicate that strongly electron-withdrawing groups increase the cyclization barrier, while sigma-donating groups decrease it; pi conjugation, especially donation, has little effect. Most annulations, including those involving heteroaromatic rings, lower the barrier slightly (6 MR) or raise it slightly (5 MR). Larger effects are seen for smaller rings or charged rings. Some previously observed apparent rate inhibitions are seen to be due to reversibility or forward reactivity of the intermediate p-benzynes, which are thereby inhibited from the H abstraction step that completes cycloaromatization. H abstraction reactivity, as judged from the p-benzyne singlet-triplet energy gap and from isodesmic equations, is also examined. Unexpected behavior is predicted for some heteroaromatic systems. Finally, we anticipate how these results may be applied to the design of prodrug candidates for subsequent biological application.
Chemistry, Organic↗
Changes in plasma levels of prolactin, in relation to those of FSH, oestradiol, androstenedione and progesterone around the preovulatory surge of LH in women.
Plasma samples were obtained at 8 hourly intervals around the preovulatory surge of LH in three groups of women with spontaneously ovulatory menstrual cycles, in order to clarify the hormonal events around the time of ovulation. In 21 of 25 women in whom samples were collected every 8 hours the start of the LH surge occurred between midnight and 0800. In 16 of these women the concentration of LH, FSH and progesterone was measured every 8 hours around the pre-ovulatory surge of LH. A progressive increase in progesterone started with the onset of the LH surge, with a transient fall after 32-40 h at a time coincident with that of ovulation. In 10 women oestradiol, androstenedione and prolactin were measured 8 hourly around the pre-ovulatory surge of LH beginning at 0800 h. Prolactin showed a sustained increase in levels beginning at the start of and lasting for the duration of the pre-ovulatory LH surge; oestradiol levels did not rise around this time, and declined by 24 h after the onset of the LH surge. These results suggest that (1) the pre-ovulatory LH surge begins between midnight and 0800 h in the majority of women, (2) luteinization of the granulosa cells within the pre-ovulatory follicle occurs in response to the LH surge, (3) the increase in prolactin at the time of the LH surge is not directly related to increasing levels of oestradiol but may be due to a decrease in hypothalamic inhibition of prolactin secretion which occurs coincident with the release of LHRH associated with the preovulatory LH surge.
Adult↗
Heart failure management.
Patients with congestive heart failure consume a large portion of healthcare dollars. After the implementation of an outpatient inotropic infusion unit, case management, a restorative care pathway, and telemanagement at a community hospital, the number of hospital admissions, the inpatient length of stay, and overall costs decreased. At the same time, customer satisfaction and functional status increased. This article describes how the improved outcomes were accomplished.
Activities of Daily Living↗
Current management of purpura fulminans: a multicenter study.
Seven burn centers performed a 10-yr retrospective chart review of patients diagnosed with purpura fulminans. Patient demographics, etiology, presentation, medical and surgical treatment, and outcome were reviewed. A total of 70 patients were identified. Mean patient age was 13 yr. Neisseria meningitidis was the most common etiologic agent in infants and adolescents whereas Streptococcus commonly afflicted the adult population. Acute management consisted of antibiotic administration, volume resuscitation, ventilatory and inotropic support, with occasional use of corticosteroids (38%) and protein C replacement (9%). Full-thickness skin and soft-tissue necrosis was extensive, requiring skin grafting and amputations in 90% of the patients. One fourth of the patients required amputations of all extremities. Fasciotomies when performed early appeared to limit the level of amputation in 6 of 14 patients. Therefore, fasciotomies during the initial management of these patients may reduce the depth of soft-tissue involvement and the extent of amputations.
Adolescent↗