Current Organic Chemistry - Volume 23, Issue 17, 2019

The quinoxaline derivatives are beneficial compounds because of their various medicinal and industrial applications. They are well-known for application in organic light emitting devices, polymers and pharmaceutical agents. The quinoxaline-containing polymers are applicable in optical devices due to their thermal stability and low band gap. There are many reported procedures for the synthesis of bis- and polyquinoxalines and quinoxaline-containing macrocycles. The quinoxaline-based compounds as fascinating structures are important subjects of interest in either basic or applied sciences. This review summarizes the latest progresses related to the quinoxalines, quinoxaline-containing macrocycles, and bis- and poly quinoxalines, including the synthesis, functionalization and modification methods and applications of these compounds.

In this review, the species from the genus Eremostachys Bunge are described and explored from different standpoints. In particular, the main attention is focused on phytochemistry also with reference to the biogenesis of the most important class of chemotaxonomic marker, the iridoids, and their co-occurrence with volatile terpene components of essential oils which own the same biogenetic precursors. The ethnopharmacological implications of the plants belonging to this genus are also reported in detail. Nevertheless, a few morphological and botanical details of Eremostachys are also presented, as well as some topics about its chemotaxonomy and pure pharmacology. Based on the data reported in the literature, different species of the genus Eremostachys show important and interesting peculiarities under all these aspects that are extensively discussed and commented.

Partially reduced heterocyclic compounds such as 1,4,5,6-tetrahydropyrimidines are often found to possess interesting pharmacological properties. Yet, the synthetic routes towards such systems are less developed than their fully aromatic counterparts. In this review article, the biological significance of 1,4,5,6-tetrahydropyrimidines is discussed and the existing literature reports describing various preparative routes to access 1,4,5,6-tetrahydropyrimidine derivatives have been categorically described. The focus has been expanded to present an overview of the chronological development of the traditional synthetic routes as well as the contemporary approaches to 1,4,5,6-tetrahydropyrimidines that generally include: (i) condensation reactions of diamines with various appropriate counterparts such as carbonyl compounds, imino ethers, amidines or nitriles, condensation of amidines with 1,3-dibromopropane and α,β-unstaurated carbonyl compounds, condensation of amino alcohols; (ii) selective reduction of pyrimidines; (iii) ring expansion chemistry of cyclopropanes, aziridines, and azetidines; and (iv) miscellaneous examples such as various multicomponent reactions.

Three new 5-deoxyflavonoid and dihydroflavonoids 2, 3 and 4 have been isolated from the methanolic extract of Abutioln pakistanicum aerial parts, for which structures were elucidated explicitly by extensive MS- and NMR-experiments. In addition to these, 3,7,4′-trihydroxy-3′-methoxy flavonol (1) is reported for the first time from Abutioln pakistanicum. Compound 2 and 4 are p-coumaric acid esters while compounds 2–4 exhibited α-glucosidase inhibitory activity. Docking studies indicated that the ability of flavonoids 2, 3 and 4 to form multiple hydrogen bonds with catalytically important residues is decisive hence is responsible for the inhibition activity. The docking results signified the observed in-vitro activity quite well which is in accordance with previously obtained conclusion that phenol moiety and hydroxyl group are critical for the inhibition of α-glucosidase enzyme.

Seven selected chiral mono-, di-, and tridentate amines supported on insoluble polymer were effectively prepared from corresponding primary amines or secondary amino alcohols and Merrifield resin. The reaction of the polymer-supported amines with excess n-butyllithium gave the corresponding lithium amide bases, which were tested in the aldol reactions of tropinone with benzaldehyde. The deprotonation reactions were carried out with or without separation of the lithium enolate from polymer-supported reagents. Using the procedure with separation of lithium enolate from supported chiral reagent different results were obtained with or without the addition of LiCl despite the fact that aggregate formation of Merrifield resin supported Li-amides is hindered. Without the additive, the aldol products were obtained in low diastereoselectivity and enantioselectivity, whereas the addition of LiCl resulted in a significant increase of de and ee even when LiCl was added after the deprotonation step and separation of the chiral amine.