Parent with side chains

Diastereoisomers of 24-alkylated sterols can be distinguished by C n.m.r. The preferred conformation about the C-24—C-25 bond depends on the configuration at C-24, with distinguishable shielding effects on the C-26 and C-27 of the parent cholestane side-chain. Other authors report n.m.r. data for (245)-24-ethylcholesterol (/8-sitosterol) and for )- and (Z)-24-ethylidene-cholesterols (14) (fucosterol and isofucosterol) and their acetates. 

Substitution on the phenyl ring of antifolates was described as early as 1951 by Cosulich et al. [192] in the form of 3 -chloroAMT (V.l), 3 -broraoAMT (V.2), and 3 -chloroMTX (V.3), which were obtained by chlorination or bromination of the parent compounds in AcOH. Other 3 -chloro compounds reported by the Lederle group [192] were the A -nitroso, 9,10-dimethyl ( adenopterin ), 2-AW-dimethylamino and 4-piperidino analogues, as well as several with side-chain moieties other than glutamic acid. Compound (V.3)... 

Some of the preparative methods for alkyl phenols and their reactions are unique to this class and both therefore warrant separate treatment from the parent compound. These features are even more prevalent in the hindered phenols a group of substances first synthesised less than half a century ago. In this account the synthesis of alkylphenols bearing purely methylenic side-chains in the benzenoid, naphthalenic and polycyclic series are considered first. Alkylphenols with side-chains containing oxy or alkoxycarbonyl groups are then reviewed, followed by mention of those containing Si, N or S in the side-chain and finally polycyclic types with saturated and unsaturated rings bearing hetero atoms. As before emphasis has been placed on developments in the last decade. 

The stmcture of vitamin A [11103-57-4] and some of the important derivatives are shown in Figure 1. The parent stmcture is aH-Zra/ j -retinol [68-26-8] and its lUPAC name is (all-E)-3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexen-l-yl)-2,4,6,8-nonatetraen-l-ol (1). The numbering system for vitamin A derivatives parallels the system used for the carotenoids. In older Hterature, vitamin A compounds are named as derivatives of trimethyl cyclohexene and the side chain is named as a substituent. For retinoic acid derivatives, the carboxyl group is denoted as C-1 and the trimethyl cyclohexane ring as a substituent on C-9. The stmctures of vitamin A and -carotene were elucidated by Karrer in 1930 and several derivatives of the vitamin were prepared by this group (5,6). In 1935, Wald isolated a substance found in the visual pigments of the eye and was able to show that this material was identical with Karrer s retinaldehyde [116-31-4] (5) (7). 

Omission of the side chain methyl group also leads to an active analgesic, the potency of which is somewhat less than half that of the parent. Alkylation of the familiar nitrile with N (2-chioroethyl)dimethylamine gives the amine, 126. Reaction with... 

The carbon atoms of the parent chain are numbered according to 2-Carb-2.2.1. If a unique numbering is required for the branch(es) (e.g. for X-ray orNMR work), the carbon atoms may be given the locant of the appropriate branch point, with the internal branch locant as superscript, e.g. 42 for position 2 of the branch at position 4 of the main chain. This style of branch numbering is not to be used for naming purposes e.g. the side-chain-methylated derivative of compound 5 is named 4,6-dideoxy-3-C-[(I )-1 -methoxyethyl]-D-n7w-hexose, and not as a s -O-methyl derivative. 

The logical continuation of the stepladder strategy outlined above for minimizing the mutual distorsion of adjacent main chain phenylene units was the incorporation of the complete PPP-parent chromophore into the network of a completely planar ladder polymer. The complete flattening of the conjugated 7T-system by bridging of all the subunits should then lead to maximum conjuga-tive interaction. As with the PTHP 11 systems, alkyl or alkoxy side chains should lead to solubilization of the polymers. 

Reaction of 518 with various bifunctional compounds such as a-halogeno acids or esters results in the isolation of fused heterocyclic systems such as 520 [87IJC(B)110]. The factors affecting cyclization are dependent on the cyclizing agent as well as the nature of the side chain present in the parent compound. 

---