Total Synthesis of the Sesquiterpene (-)-Merrillianin.

The first total synthesis of (-)-merrillianin (1), which is a natural sesquiterpene with a tricyclic structure having a cyclopentane ring and five- and seven-membered lactone parts, is demonstrated. This asymmetric total synthesis enabled the absolute stereostructure determination of naturally occurring (-)-1.

Enantioselective synthesis of the optically active alpha-methylene-beta-hydroxy esters, equivalent compounds to Morita-Baylis-Hillman adducts, using successive asymmetric aldol reaction and oxidative deselenization.

[Chemical reaction: See text] The asymmetric aldol reaction of a tetra-substituted ketene silyl acetal including an alkylseleno group with aldehydes has been developed by the promotion of Sn(OTf)2 coordinated with a chiral diamine to afford the corresponding aldols having chiral quaternary centers at the alpha-positions. The facile oxidative deselenization of these aldol compounds produces optically active alpha-methylene-beta-hydroxy esters which correspond to adducts prepared by the asymmetric Morita-Baylis-Hillman reaction.

Enantioselective total synthesis of octalactin a using asymmetric aldol reactions and a rapid lactonization to form a medium-sized ring.

Octalactin A, an antitumor agent containing an eight-membered lactone moiety, has been stereoselectively prepared by means of enantioselective aldol reactions of selected silyl enolates with achiral aldehydes, promoted by a chiral Sn(II) complex. The medium-sized lactone part was effectively constructed by way of a new and rapid mixed-anhydride lactonization using 2-methyl-6-nitrobenzoic anhydride (MNBA) with a catalytic amount of 4-(dimethylamino)pyridine (DMAP) or 4-(dimethylamino)pyridine 1-oxide (DMAPO). The use of only 5 mol % of DMAP or 2 mol % of DMAPO rapidly promoted formation of the medium-sized ring of the octalactin, demonstrating the remarkable efficiency of the new lactonization protocol.

The effect of occlusal alteration and masticatory imbalance on the cervical spine.

The characteristics of mandibular lateral displacement include lateral inclination of the occlusal plane and the differences between the right and left masticatory muscles. The aims of this investigation were to compare the mandibular stress distribution and displacement of the cervical spine using three-dimensional finite element models (3D FEM) to simulate masticatory movements and to clarify the association between morphological and functional characteristics and head posture. A symmetrical standard model was produced (model-A). Model-B had higher masticatory muscle strength on the left side, model-C had symmetrical masticatory muscle strength but the occlusal plane was inclined upwards towards the right and model-D had the occlusal plane inclined upwards towards the right with higher masticatory muscle strength on the left side. Model-A showed a completely symmetrical stress distribution pattern, while in model-B there was an uneven distribution in the mandible with higher stress on the left side. In addition, the stress distribution in the cervical spine was asymmetrical, showing displacement to the right. Model-C showed a similar mandibular tendency to model-B but the opposite tendency in the cervical spine. In model-D, the mandibular stress distribution was markedly asymmetrical, but almost symmetrical in the cervical spine with markedly decreased lateral displacement. These results suggest that lateral inclination of the occlusal plane and imbalance between the right and left masticatory muscles antagonistically act on displacement of the cervical spine, i.e. the morphological and functional characteristics in patients with mandibular lateral displacement may play a compensatory role in posture control.

Stresses on the cervical column associated with vertical occlusal alteration.

The biomechanical effects on cervical vertebral columns (C1-C7) during mastication were calculated using a three-dimensional (3D) finite element method. To verify the biomechanical influences of vertical occlusal alteration to the cervical column, three finite element models (FEM) showing a normal (model A), a steep (model B), and a flat occlusal plane (model C) were constructed. The occlusal stress distribution showed various patterns for the three models; the stress extended to the anterior area as the occlusal plane became steeper. The plots of the stresses on the mid sagittal section of the cervical columns showed different patterns for the three models; the stress converged at the odontoid process in models A and B, whereas the stresses at C7 in model B tended to decrease compared with model A. Concentrated stress was observed at C5 in model C, supporting the hypothesis that vertical occlusal alteration could influence stress distribution in the cervical columns.

Biomechanical influences of head posture on occlusion: an experimental study using finite element analysis.

The biomechanical influences of head posture on the cervical column and craniofacial complex during masticatory simulation were quantified using three-dimensional (3D) finite element analysis (FEA). Three types of finite element model (FEM) were designed to examine relationships between the position of the head and malocclusion. Model A was constructed to have a standardized cervical column curve, model B a forward inclined posture, and model C a backward inclined posture. The results of the spinal displacements revealed that model B moved in a forward direction and model C in a backward direction during masticatory simulation. The stress distributions on the cervical column (C1-C7) for models A, B, and C showed differences; stress converged at the atlas in model A, high-level stresses were observed at the spinous processes of C6 and C7 in model C, and the stress converged at the anterior edge in the vertebral body of C4 of model B. Stress distribution on the occlusal plane and maxillofacial structure did not show absolute differences among the three models. Alteration of head posture was directly related to stress distribution on the cervical column, but may not always directly influence the occlusal state.

An experimental study on mandibular expansion: increases in arch width and perimeter.

The purpose of this study was to estimate the increase in arch perimeter associated with mandibular lateral expansion. The mandibular expansion was simulated using a three-dimensional (3D) finite element method (FEM) and a computer graphics technique (3D simulation). The centre of rotation of molars during movement accompanied by lateral expansion was calculated using 3D FEM. The geometry of the model was determined using the mandibular bone of an East Indian skeletal specimen and 1 mm computer tomogram (CT) slices. The 3D set-up simulation was then conducted using 3D computer graphics instead of performing a manual set-up. Rotational movement was induced in the buccal segment, from the first premolar to second molar, in the 3D set-up model around the location of the centre of rotation (4.5 mm below the root apex of the first molar) derived from the FEM. According to 3D simulation, the model showed an opening space of 1.43 mm between the canine and first premolar, and thus a change in arch perimeter of 2.86 mm. The tip of the mesio-lingual cusp of the first molar moved 3.88 mm laterally, resulting in a change in inter-molar width of 7.76 mm. These values mean that a 1 mm increase in arch width resulted in an increase in arch perimeter of 0.37 mm. This result would be of value clinically for prediction of the effects of mandibular expansion.