Conformational constraints: nonpeptide beta-turn mimics

The beta-turn, which has also been referred to as the beta-bend, beta-loop or reverse turn, has been implicated as an important site for molecular recognition in many biologically active peptides and in globular proteins. This small secondary structure therefore makes an attractive target for mimicry by a conformational constraint, because a peptide which is constrained in a biologically active conformation can display a number of advantages over the parent substrate. The less peptide-like such a constraint is, the more potential there is to maximize these advantages. A decade has passed since the first (and highly successful) attempt to mimic the beta-turn with a nonpeptide conformational constraint was disclosed by Freidinger et al. (1980). Since this report, rapidly growing interest in the field of nonpeptide beta-turn mimics has seen a variety of experimental approaches and a mixed bag of results. It is attempted in this review, not only to summarize and critically analyse these approaches, but also to touch on the complexities associated with the conformational mimicry of such a diverse structure as the beta-turn.

Computed tomography of the major and minor fissures

One hundred computed tomograms of patients with normal lungs were reviewed to determine the normal characteristics of the major fissures and the minor fissure and how often each is seen. Each major fissure was imaged most often as a lucent band, less often as a line, and least often as a dense band. The percentage visualization of these three appearances is tabulated for the upper, middle, and lower parts of each major fissure. The minor fissure was imaged as a lucent area. The lucent area was more often triangular, with its apex at the hilar region, and less often round or oval. Several examples are presented to illustrate how an understanding of the fissures, as displayed cross-sectionally, helps in interpreting abnormal findings on computed tomographic scans. These examples relate to localization of masses within the lobes of the lung, extension of carcinoma to or across the fissure, recognition of fluid in the fissure, etc.

Direct oblique sagittal CT of orbital wall fractures

Direct oblique sagittal CT was used to evaluate trauma to 77 orbits. Sixty-seven orbital wall fractures with intact orbital rims (36 floor, 22 medial wall, nine roof) were identified in 47 orbits. Since persistent diplopia and/or enophthalmos may warrant surgical repair of orbital floor fractures, optimal imaging should include an evaluation of extraocular muscle status, the nature and amount of displaced orbital contents, and an accurate definition of fracture margins. For orbital floor fractures, a combination of the direct oblique sagittal and direct coronal projections optimally displayed all fracture margins, the fracture's relationship to the inferior orbital rim and medial orbital wall, and the amount of displacement into the maxillary sinus. Inferior rectus muscle status with 36 floor fractures was best seen on the direct oblique sagittal projection in 30 fractures (83.3%) and was equally well seen on sagittal and coronal projections in two fractures (5.5%). Floor fractures were missed on 100% of axial, 5.5% of sagittal, and 0% of coronal projections. Since the direct oblique sagittal projection complements the direct coronal projection in evaluating orbital floor fractures, it should not be performed alone. A technical approach to the CT evaluation or orbital wall fractures is presented.

Endoscopic bougie and balloon dilatation of multiple bronchial stenoses: 10 year follow up

This paper reports 10 year follow up data on four patients who underwent mechanical dilatation of multiple bronchial stenoses (sarcoidosis two cases, berylliosis one case, idiopathic stenoses one case). Two patients enjoyed symptomatic and physiological improvement during the nine years before they presented with a recurrence of stenosis. The other two had recurrences sooner, and improved only slightly after they had started prednisolone treatment.

The variable appearance of the left superior intercostal vein

The authors reviewed several hundred postero-anterior chest radiographs to document the location and appearance of the left superior intercostal vein, which was seen in 9.5% of patients. Variations in the location of this vein when seen end-on as the aortic "nipple", and in the appearance of the "retroaortic" portion (the result of contact with aerated lung), are discussed. The "retroaortic portion" may be seen through the aortic knob.

Complications of intravenous digital subtraction angiography

Extracranial carotid occlusive disease can be evaluated with either intravenous (IV) digital subtraction angiography (DSA) or standard angiography. In a prospective study, complications related to 500 IV DSA examinations occurred in 16.6% of patients, including local complications in 2.0%, systemic complications in 15.0%, and neurologic complications in 3.0%. A permanent neurologic deficit occurred in one patient. Complications related to 150 standard angiograms occurred in 7.3% of patients, including local complications in 4.0%, systemic complications in 3.4%, and neurologic complications in 0.7%. There were no permanent neurologic deficits. Serious systemic and neurologic complications occurred in 8.2% of patients during IV DSA and 2.7% of patients during standard angiography. The rapid injection of high volumes of hypertonic contrast media during IV DSA and the resultant hemodynamic and cardiac electrophysiologic changes account for the higher incidence of complications with IV DSA.

Cardiac tamponade

Cardiac tamponade is a cardiological emergency requiring prompt treatment in order to avoid a fatal outcome. It can complicate a number of medical conditions and it is important, therefore, that all practitioners are aware of its presentation, diagnosis and management. These are outlined. We suggest that, with certain specific and important exceptions, percutaneous catheter pericardiocentesis is to be recommended in the management of cardiac tamponade. We include a review of 51 consecutive cases treated at our own institution. Catheter pericardiocentesis was successful in 49 (96%) cases and 36 (80%) patients did not require any further intervention. There were no major and only two minor complications which required no additional treatment. We review previous literature concerning percutaneous pericardiocentesis. Using recommended procedures, pericardiocentesis is successful in 90-100% of cases and major complications are rare.

Anterior sacral meningocele. Current diagnosis

One hundred fifty cases of anterior sacral meningocele have been reported in the world literature. This rare pathologic entity was first recognized and described by Bryant in 1837. We report a patient with an incidental anterior sacral meningocele. Our patient is the oldest reported in the literature. The incidental feature of this malformation is uncommon. We review the literature and discuss the clinical aspect, diagnosis, and treatment. Emphasis is placed on the current and optimal method of radiologic evaluation using computed tomography scan combined with metrizamide myelography.

Experience with cardiac tamponade following open heart surgery

Cardiac tamponade following open heart surgery is well described, although, fortunately, uncommon. Unlike more classical "primary" tamponade, the clinical features are not specific, and this can delay diagnosis. In practice, the threshold for investigation must be low, and echocardiography has been invaluable in the detection and localization of pericardial collections. Several factors are believed to contribute to the likelihood of postoperative tamponade, but the mechanisms are not clearly understood. Resternotomy, under general anesthesia, or subxiphoid pericardiotomy, under local or general anesthesia, are effective forms of treatment. However, recent success with the use of percutaneous pericardiocentesis under echocardiographic guidance has shown that postoperative tamponade can be treated safely and effectively by this method.

A one-variable topographical descriptor for the beta-turns of peptides and proteins

The beta-turn is a common secondary structure in biologically active peptides and globular proteins, where it is widely thought to serve as a molecular recognition site for many biological processes. Although the primary beta-turn recognition requirements are thought to be straightforward, relating mainly to the relative positions of the peptide sidechains, current classifications of beta-turns are complex and are based solely upon the very variable geometry of the peptide backbone. We demonstrate here that beta-turns can be described in terms of a single dihedral angle, which we have called beta, which provides a complete description of the spatial relationship between the entry and exit peptide bonds as well as the relative orientations of the intervening sidechains for any beta-turn. This description should prove particularly useful in the development and application of novel peptide mimetic drugs, compounds for which a classification based on a peptide backbone geometry may be entirely irrelevant.

The superolateral major fissures

In a review of more than 1,000 posteroanterior views of normal adult chests, a curving contour that relates to the major fissure laterally along the superior segment of the lower lobe was identified in 14%. The contour, which was more often seen as an edge rather than a line, was noted only on the right in 4%, only on the left in 6%, and on both the right and the left in 4% of patients. This publication discusses various characteristics of the curving contour, evidence that relates the contour to the major fissure, and the mechanism of production of the curving contour when seen as an edge. Also presented are some clinical examples illustrating the usefulness of understanding this feature of radiographic anatomy.

Prognostic features of large cell anaplastic carcinoma of the bronchus

The clinical features of 208 patients with large cell anaplastic carcinoma of the bronchus are reviewed. Of the sample 47.6% had disseminated disease at presentation, and 95% were cigarette smokers. The median survival was 6.0 months and five-year survival was 5.9%. Twenty-seven per cent of the patients had surgical resection of tumour. The median survival of resected patients was 13.0 months and five-year-survival was 21%. Radiotherapy was ineffective in controlling the disease in this series.

The left paratracheal reflection

The left paratracheal reflection, which is found medial to the left subclavian artery reflection, was sought in 302 normal posteroanterior (PA) chest radiographs, 93 conventional chest tomograms, and 113 thoracic computed tomographic (CT) scans. The left paratracheal reflection was visible on 31% of normal PA chest radiographs. Conventional tomography and CT showed that this finding is produced by contact of the lung with the mediastinum anterior to the left subclavian artery. The CT scans studied showed that the left paratracheal reflection actually represents contact of the lung with left paratracheal mediastinal fat 94% of the time, with the proximal 1-2 cm of the lateral wall of the left common carotid artery 5% of the time, and with the left tracheal wall 1% of the time. A variety of entities may alter the left paratracheal reflection.

Synthesis and Conformational Analysis of the Slime-Mold Acrasin Glorin

The chemotactic dipeptide for the slime-mould Polysphondylium violaceum, glorin (N- propionyl-y-L-glutamyl-L-ornithine-δ-lac ethyl ester) (8), was synthesized convergently in five steps with 41% overall yield, starting from L- ornithine hydrochloride (1) and L- glutamic acid γ-benzyl ester (4). -1H n.m.r. spectral analysis led to the conclusion that the propionamide and the γ-L- glutamyl amide bonds both undergo slow cis-trans isomerism in solution at room temperature. From a Karplus-type analysis of the values of the Cα,Cβ coupling constants at the lactam chiral carbon, it was concluded that the six-membered ring can adopt either a half-chair or half-boat conformation, but it is not clear which. Similar calculations for the glutamyl Ca,Cβ coupling constants were performed and, from these, significantly different relative populations for the three staggered conformations about the Glu-Ca,Cβ bond were suggested. Receptor binding studies showed that glorin did not bind significantly to any of the six receptors studied, including opioid, dopamine, central benzodiazepine, peripheral benzodiazepine, α1-adrenoceptor and α2-adrenoceptor sites.