This paper reports the use of p‐phenylenediamine to prepare bis‐Tröger’s bases. The methyl,nitro‐substituted bis‐Tröger’s base 5, already previously prepared by another procedure, was obtained in fewer steps, although with no improvement in the yield of the desired syn isomer. The symmetric dinitro‐substituted bis‐Tröger’s base 17, which cannot be prepared by the older method, was then synthesized. Its structure was determined by mass spectrometry, 2D NMR spectroscopy, and, in the case of the syn isomer, by X‐ray crystallography. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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The total synthesis of apigeninidin (1), luteolinidin (2) and 5,7-dihydroxyflavylium (5) chlorides is performed through a one step reaction from an acetylated derivative of a commercial reagent. Condensation reaction between 2,4,6-triacetoxybenzaldehyde and an acetophenone derivative in anhyd methanolic hydrogen chloride provides the 3-deoxyanthocyanidins in high yields.Apigeninidin (1) and luteolinidin (2) chlorides ( Figure 1) are the most common of the natural 3-deoxyanthocyanidins, a group of yellow-orange flavylium pigments. 2 These 5,7-dihydroxyflavylium salts, possessing at least one additional hydroxyl group in the 4¢ position, are contained in food plants such as corn and sorghum. 3 Apigeninidin has been earlier investigated as a food colorant, 4 and hair dye preparations containing this substance have more recently been patented, 5 which underlines the possible industrial use of these colored derivatives.In previous studies, 6-8 we have shown that natural 3-Oglucosylated flavylium salts (the monoglucosylated anthocyanins from Vitis vinifera grapes) possess DNA triplex stabilizing properties. Such properties are useful in the antigene strategy, a potential therapeutic approach consisting in the regulation of gene expression by nucleic acids, since one of its limitations pertains to the weak stability of the triplex formed between a target duplex and a synthetic oligonucleotide. 6,7,9 Concerning the stabilizing properties of the monoglucosylated flavylium salts previously studied, we have demonstrated that the sugar moiety at their 3 position could preclude efficient interaction with the triplex and so limit the activity. 6 Thus, we decided to study non-glucosylated derivatives such as 1 and 2, 6,7 that we have chosen to obtain by total synthesis, since their extraction is greatly time-consuming and leads generally to only small amounts of substances. In the present work, we report a new and convenient synthesis of these cationic derivatives.The synthesis of apigeninidin and luteolinidin chlorides were firstly realized by Robinson et al. in the thirties by condensation between an acetophenone and a protected phloroglucinaldehyde. 10 The products were however generally obtained as crude mixtures after three or four steps and in 30% yields in the best cases. More recently, in the eighties, Sweeny and Iacobucci carried out a method in which these natural derivatives were synthesized through an oxidative decarboxylation of the corresponding 4-carboxy-2-flavenes obtained from Bülow's intermediates. 11 This synthesis proceeds in four steps and in overall yields of around 40% from phloroglucinol dimethyl ether. Another method consists in the chemical conversion of flavonoid precursors: Sweeny and Iacobucci thus obtained apigeninidin chloride in two steps from 4¢,5,7-triacetoxyflavan in 21% yield. 12 All these reactions, though leading to the desired compounds, proceed in several steps and in limited yields. Moreover, mixtures of organic salts are often formed during these syntheses, which can greatly complicate ...

Dedicated to Professor Rolf Huisgen on the occasion of his 85th birthday Four novel molecular tweezers, 6 ± 9, have been synthesized having, for the first time, three fused Trögers bases. The compounds differ in the relative configuration of the three fused methylene bridges and have been unambiguously characterized by NMR.Introduction. ± Trögers base (1) [1] is a concave chiral molecule, the chirality of which results from the blocked configuration of its stereogenic N-atoms. Trögers base and its derivatives have been described as fascinating molecules [2]. They provide relatively rigid chiral frameworks for the construction of chelating and biomimetic systems, which were essentially developed by Wilcox and co-workers, and elaborated by others [3]. Trögers bases show a perpendicular arrangement of the two aromatic rings [3c], as in Kagans ether, which was used by Harmata and co-workers for the synthesis of molecular tweezers [4]. In this context, we have utilized the Trögers base skeleton as a scaffold for the construction of the molecular clips 2 [5], 3 [6], and 4 [7].In this paper, we report the synthesis of chiral molecular tweezers with a trimeric, fused Trögers base skeleton. During the course of the present work, Klärner et al. [8] have described the synthesis of another family of molecular tweezers of type 5, with three methylene bridges, achiral carbocylic analogues of the compounds described in this paper.