Hydroxylation pattern

A different type of reactive bromo compound having a moderate resemblance to hexoses is represented by the bromoconduritols B (40) and F (41), named after the respective parent tetrahydroxycyclohexene. Even thou their hydroxylation pattern resembles that of D-glucose, only a few examples of D-glucosidase inhibition have been reported. The first was a-D-glucosi-dase from yeast, which is inhibited by bromoconduritol B (formerly called bromoconduritol A), having ki(max)/Kj 69,000 M" min", by alkylation of a histidine residue at the active site. 

In a few species, the B-ring hydroxylation pattern is thought to be fully or partially determined through the HCA-CoA ester used by CHS (see Section 3.4.1). However, most commonly hydroxylation at the C-3 and C-5 positions is determined at the C15 level by the activity of two P450s, the F3 H and F3, 5 H. Genes and cDNAs for both enzymes, sometimes informally referred to as the red and blue genes because of their impact on flower color, were first cloned and characterized from Petunia and subsequently from several other species (listed in Ref. 5). Based on sequence analysis, the F3 H and F3, 5 H proteins are 56 to 58 kDa in size. 

Proanthocyanidins of the B-type are characterized by singly linked flavanyl units, usually between C-4 of the chain-extension unit and C-6 or C-8 of the chain-terminating moiety. They are classified according to the hydroxylation pattern of the chain-extension units (see T able 11.1). 

The fundamental nucleus in anthocyanidins (aglycones) is flavylium chloride. Most of the anthocyanidins are derivatives of 3,5,7-trihydroxyflavylium chloride. Thus, the hydroxylation patterns in the natural anthocyanidins fall into the three basic groups of pelargonidin, cyanidin and delphinidin. Anthocyanidins are rarely found in fresh plant material because of their instability [19]. 

Rama Rao, A.V., Sarma, M.R., Venkataraman, K. and Yemul, S.S. (1974) A benzophenone and xanthone with unusual hydroxylation patterns from the heartwood of Carcinia pedunculata. Phytochemistry 13(7), 1241-1244. 

From the viewpoint of the steroid structure, SAAF (30) has several unique features. The hydroxylation pattern at the 3, 4, 7, and 26 positions of a cholestane skeleton has not been reported in any other natural products.73 The positions of the C-3 and C-26 sulfate esters are also unique among sulfated polyhydroxysterols of marine origin. In general, steroid hormones act on nuclear receptors and activate gene expression. However, the chemotactic behavior of sperm occurs within a few seconds, and the sperm nucleus is condensed, indicating that genes could not be expressed in the sperm. Furthermore, since SAAF has a hydrophilic nature due to the presence of two hydroxyl and two sulfated esters, it may bind to receptors located on the sperm plasma membrane. 

Figure 7.1 Two dimension paper chromatography of plant extracts. The methanol-water extract is deposited in the application point (origin), dried, and developed with BAW (M-Butanol/acetic acid/water 4 1.5, upper phase) and 15% or 30% HO Ac (acetic acid). (A) Flavonoid aglycones with different hydroxylation patterns (B) Flavone monoglycosides (C) Flavone di- and tri-glycosides (D) Flavone di- and triglycosides acylated with hydroxycinnamic acids).

Several proanthocyanidin classes can be distinguished on the basis of the hydroxylation pattern of the constitutive units. Among them, procyanidins, consisting of (epi)catechin units (3, 4 di OH), and prodelphinidins, deriving from (epi)gallocatechin (3 ,4, 5 tri OH), Figure 2, have been reported in grapes. 

U. tomentosa and E.japonica appear to be generous sources of novel highly hydroxylated urs-12-en-28-oic acid derivatives. The 3p, 6a or 6p, 19a hydroxylation pattern is a common feature of the metabolites from both plants other common hydroxylated sites arc C-2 and/or C-23. 

The chemical shift of Me-24 and CH20-23 testify that the ester linkages are between the C-23 position and the gicoumaroyl moieties. Compound 13 has the same 2a, 3p, 19a, 23 hydroxylation pattern as 11 and 12 but links a caffeoyl moiety at C-3. Compound 14 is a derivative of rotundic acid which links a trans-p-coumaroyloxy moiety at C-3. 

Two human urinary metabolites of phencyclidine (PCPi have been identified as the 4-hydroxypiperidyl and 4-hy-droxycyclohcxyl derivatives of the parent compound. " Thus, from these results, it appears that alicyclic" hydroxylation of the six-memhered piperidyl moiety may parallel closely the hydroxylation pattern of the cyclohexyl moiety. 

The reactive properties of the haem group and Compound I may be affected by the particular protein environment of a specific cytochrome P450. Different P450 isoenzymes show very different substrate specificity, and hydroxylation patterns. These could be the result of orientation or binding effects,188 or the... 

A wide variety of flavonoid compounds have been isolated from hardwoods, including flavones, flavanols, flavanones, isoflavones, and chalcones, most of whieh are highly hydroxylated, and which vary in hydroxylation pattern. Two of the many compounds present are shown in Figure 2.17 robinetin is the 3-hydroxy-flavone extracted from Robinia and Intsia sp. while the chalcone, okanin, is found in Cyclodiscus sp. 

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