Root Canal Anatomy of Maxillary and Mandibular Teeth

It is a common knowledge that a comprehensive understanding of the complexity of the internal anatomy of teeth is imperative to ensure successful root canal treatment. The significance of canal anatomy has been emphasized by studies demonstrating that variations in canal geometry before cleaning, shaping, and obturation procedures had a greater effect on the outcome than the techniques themselves. In recent years, significant technological advances for imaging teeth, such as CBCT and micro-CT, respectively, have been introduced. Their noninvasive nature allows to perform in vivo anatomical studies using large populations to address the influence of several variables such as ethnicity, aging, gender, and others, on the root canal anatomy, as well as to evaluate, quantitatively and/or qualitatively, specific and fine anatomical features of a tooth group. The purpose of this chapter is to summarize the morphological aspects of the root canal anatomy published in the literature of all groups of teeth and illustrate with three-dimensional images acquired from micro-CT technology.info:eu-repo/semantics/publishedVersio

Diastereoselectivity in Passerini Reactions of Chiral Aldehydes and in Ugi Reactions of Chiral Cyclic Imines

Diastereoselectivity in Passerini and Ugi reactions of chiral aldehydes/imines remains challenging. Moreover, the Ugi reaction of chiral acyclic imines is complicated by their easy racemization/epimerization, whereas this problem is nearly completely suppressed using chiral cyclic imines in a modification called Ugi-Joulli\ue9 reaction. Thus 3-component modification also allows a better diastereoselectivity thanks to the higher steric rigidity of rings. This review presents an overview of the current knowledge on diastereoselective Passerini reaction of chiral aldehydes, and on diastereoselective Ugi-Joulli\ue9 reaction of chiral cyclic imines, focusing on the results gathered by the authors' research group

CHAPTER 6: Renewable Starting Materials, Biocatalysis, and Multicomponent Reactions: A Powerful Trio for the Green Synthesis of Highly Valued Chemicals

This chapter illustrates a series of recent examples on the cooperation of multicomponent reactions with biocatalysis and/or with the use of renewable starting materials derived from biomass. Teaming these three green methodologies affords important benefits from the point of view of sustainable synthesis. In particular, biocatalysts have been used to (i) generate enantiopure inputs for multicomponent reactions, (ii) resolve racemic multicomponent products, and (iii) catalyze the multicomponent process itself. As far as it concerns renewable inputs, this chapter will focus on the exploitation of diols, furan derivatives, levulinic acid, and lipids

Trehalose interacts with phospholipid polar heads in Langmuir monolayers

Surface pressure-area isotherms, surface potential-area isotherms and fluorescence microscopy were employed to study the behavior of phospholipid monolayers at the air/water interface when trehalose was added to the aqueous subphase. In the presence of this sugar, the critical area corresponding to the onset of surface potential increases, indicating that trehalose is participating in the network of hydrogen bonds between the phospholipid polar heads. In addition, it causes an expansion of the isotherm, hindering the formation of the liquid-condensed phase. The collapse area is significantly increased, indicating that trehalose takes part in the monolayer structure without being expelled even at high surface pressures. A quantitative comparison of the collapse areas and critical areas for surface potential in the presence and in the absence of the sugar shows that an almost fixed number of trehalose molecules interacts with the monolayer independently of the surface packing, thus indicating that the observed effects can be ascribed to a tight binding of trehalose to the polar heads in a defined ratio. No similar effects were observed in the presence of glucose. We rationalize the reported data in light of the water replacement hypothesis, developed to explain the preservation of biomembranes by trehalose; this hypothesis suggests that trehalose forms hydrogen bonds with the membrane polar headgroups, thus replacing the water of hydration at the membrane-fluid interface and maintaining the headgroups at their hydrated position

Stereoselective Synthesis of 3,5-Dihydroxypyrrolidin-2-ones Through a Photoinduced Multicomponent Reaction Followed by Dimerization

A photoinduced reaction between diazoketones, isocyanides and silanols, followed by aldol dimerization of the resulting multicomponent adduct, affords polyfunctionalized 3,5-dihydroxypyrrolidin-2-one heterocycles in a straightforward manner. Six new bonds and two quaternary carbons are formed in just two steps with this complexity-generating methodology. A high degree of stereoselectivity is also observed, as a result of the mild conditions employed. Moreover, the 3,5-dihydroxypyrrolidin-2-one scaffold can be found in two families of biologically relevant natural products, namely anchinopeptolides and eusynstyelamides. The synthetic approach herein described appears to be a very convenient route for the preparation of their analogues

Into the Blue: Ketene Multicomponent Reactions under Visible Light

For the first time, a detailed study on the photophysical properties of variously substituted diazoketones and on their photoreactivity under blue LED irradiation was carried out. Despite very limited absorbance in the visible region, we have demonstrated that, independently from their structure, \u3b1-diazoketones all undergo a very efficient Wolff rearrangement. Contrarily to the same UV-mediated reaction, where photons can give rise to side processes, in this case, almost all absorbed photons are selective and effective, and the quantum yield is close to 100%. If the rearrangement is carried out in the presence of isocyanides and carboxylic acids/silanols, the photoreactivity is not affected, and the resulting ketenes can afford \u3b1-acyloxy- and \u3b1-silyloxyacrylamides through two distinct multicomponent reactions, performed both in batch and under continuous flow, with improved selectivity and broader scope. These photoinduced multicomponent reactions can be coupled with other visible-light-mediated transformations, thus increasing the diversity of the molecules obtainable by this approach

The 100 facets of the Passerini reaction

This perspective aims at celebrating the 100th anniversary of the discovery of the Passerini three component reaction. After being nearly neglected for many years, now this reaction has become quite popular, thanks to the achievements of the last 30 years, which have revealed several chances of exploitation in organic synthesis. Though not being comprehensive, this review means to show the various ways that have been used in order to expand the utility of the Passerini reaction. Post-MCR transformations to give heterocycles or peptidomimetics, variants through single component replacement, stereochemical issues, and applications in total syntheses will be especially covered. This journal i

Synthesis of polyoxygenated heterocycles by diastereoselective functionalization of a bio-based chiral aldehyde exploiting the Passerini reaction

A chiral bio-based building block, prepared by the lipase-mediated desymmetrization of an erythritol derivative, was further functionalized and then submitted to stereoselective Passerini reactions, allowing the synthesis of a small library of new molecules. Thanks to the presence of different functional groups, further cyclizations were performed providing bicyclic polyoxygenated heterocycles

Diversity-oriented Synthesis of Bicyclic Heterocycles from Levulinic Acid through a Fast and Operationally Simple Multicomponent Approach

Levulinic acid, which is one of the most important renewable building blocks derived from lignocellulosic biomass, has been converted, in a diversity-oriented manner, into two families of drug-like bicyclic nitrogen heterocycles. The methodology, endowed with high step economy and operational simplicity, is based on an Ugi multicomponent reaction, which employs aminoalcohols as components, followed by a SN2 cyclization. Worth of noting is the successful synthesis of hexahydro pyrrolodiazepinediones, since the cyclization of the isocyanide-derived secondary amide onto an alcohol to give a seven-membered ring was unprecedented. Also enantiopure products have been prepared using chiral aminoalcohols

A Thorough Study on the Photoisomerization of Ferulic Acid Derivatives

A thorough study on the (E) to (Z) photoisomerization of ferulic acid derivatives (esters, amides of all types, and ketones) was carried out. At the photostationary state, only aliphatic or benzylic tertiary amides reach a nearly complete conversion of (E) isomers into the (Z) ones, whereas for esters, primary and secondary amides or aromatic tertiary amides mixtures of (Z)/(E) ranging from 7 : 93 to 72 : 28 are observed. Ketones show rather limited photoisomerization. However, (Z) ketones may be obtained by the reaction of organometal compounds with an isomerized (Z) Weinreb amide