Lateral Ring-Containing Substituents

Whereas compounds with large flexible lateral substituents, assuming that the lateral chains are oriented nearly parallel to the basic molecule, may be considered as variants of the classical rod-like molecules, compounds with lateral ring-containing substituents lead to completely new concepts of mesogens. 

In one of the first papers [7] it was reported that when isatin 7 was heated (100°C, 6 h) with acetophenone 74 in the presence of potassium hydroxide in water and alcohol 2-phenyl-4-quinolinecarboxylic acid (cinchophen) was formed with a yield of 65%. Later on [60-69] the isatins 59, containing substituents in the benzene ring, were used in the Pfitzinger reaction with the same ketone, and the similarly substituted quinolinecarboxylic acids 75 were obtained (Table 2) [12, 14, 28, 31, 60-69],... 

For example, dibenzo[18]crown-6 is a crown ether with an 18-membered macrocyclic ring containing six oxygen atoms with two benzo substituents. A more generalised system of nomenclature for such neutral organic ligands was developed by Vogtle and Weber, and later modified by in which... 

In the early studies, the phosphine oxides resolved contained substituents with aromatic condensed rings (entries 2 and 3) but later other oxides without that substitution were also resolved (entries 1 and 5) and even secondary phosphine oxides (entry 7). Entries 8-15 show some resolutions of the phosphine boranes including examples with several stereogenic centres in the backbone (entries 11-14). Compound of entry 11 can be regarded as a hybrid between BPE and DiPAMP. A few diastereomeric pairs have also been resolved by HPLC (entries 16 and 17), because conventional methods such as column chromatography or recrystallisation failed. 

Lateral substituents can be in different positions of the basic molecule [195], and lateral aromatic substituents can have several substituents themselves [191, 192] or they can be alicyclic [191]. In the so-called A-shaped mesogens [196], which occur in nematic and smectic A phases, the aromatic lateral substituents, as in older examples, are bound by carboxylic groups. Matsuna-ga etal. [20] synthesized 1,2-benzene derivatives and 2,3-naphthalene derivatives, which may be considered as compounds with ring-containing lateral substituents, attached at a terminal benzene ring. Fig. 12 presents the transition temperatures of a homologous series of this type. The first compounds of this U-shaped type were already synthesized by Vorlander and Apel [ 16]. Recent investigations by Attard et al. [187] in U-shaped compounds proved the existence of bilayers in the different smectic phases. 

Berg et al. [200] have reported on the liquid crystalline properties of four-fold substituted benzene derivatives, the structure of which may be considered as a basic molecule with two ring-containing lateral substituents (11 [200]). According to X-ray studies in the solid state, compounds of this type are cross shaped, with the ring planes... 

The avermectins are closely related to another group of pesticidal natural products, the milhemycins. First described by Japanese workers, milhemycins were later found to be more abundant in nature than the avermectins (7—12). Both the avermectins and milhemycins are sixteen-memhered lactones, with a spiroketal system containing two six-memhered rings. The principal difference between them is that the avermectins have an a-L-oleandrosyl-a-L-oleandrosyl disaccharide attached at the 13-position whereas the milhemycins have no 13-substituent. Milhemycin stmctures are shown in Figure 2. 

Tokyo Tanabe KK synthesized omeprazole analogues with an additional nitrogen in the six-membered ring of the benzimidazole moiety, but with the same substitution as omeprazole in the pyridine ring. The analogue, TU-199 (later named tenatoprazole), also contained a methoxy substituent in the benzimidazole unit, and was selected for development (Fig. 2.13). Currently, the compound has been in-licensed by the French company Negma GILD [27]. 

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