Oxidation at C l

The OH-induced oxidation of Thd at C(l ) leads to the formation of 2-dRL and the concomitant release of Thy [reactions (247) and (250) Dizdaroglu et al. 1976]. In the absence of an oxidant, 2-dRL is formed only in low yields (Table 10.27), and disproportionation reactions with other radicals present have to account for its formation. In the presence of O2, its yield is considerably increased. This raises the question as to how these reactions may proceed. 

In this context, it is worth mentioning that the C(l )-substituted C(2 ) radical undergoes rapid P-(acyloxy) alkyl rearrangement [reaction (261)], whereby a C(l )-type radical is also formed (Gimisis et al. 1995,1998). 

Being a strongly reducing radical, the C(l ) radical is also readily oxidized by Fe3+ and Cu2+. Rate constants for these reactions have been determined at -1 x 108 dm3 mol1 s1 and 7.9 x 107 dm3 mol-1 s 1, respectively (Chatgilialoglu et al. 2000). 

The C(l )-radical is also an intermediate in the free-radical-induced cylisa-tion of6-(2,2-dibromovinyl)uridine (Gimisis and Chatgilialoglu 1996). 

---

In the payoff phase, each of the two molecules of glyceraldehyde 3-phosphate derived from glucose undergoes oxidation at C-l the energy of this oxidation reaction is conserved in the formation of one NADH and two ATP per triose phosphate oxidized. The net equation for the overall process is... 

An alternative procedure for the protection of L-sorbose (25), followed by oxidation at C-l and cyclization of the product to L-ascorbic acid, was developed by Hinkley and Hoinowski.257 L-Sorbose (25) was converted into methyl a-L-sorbopyranoside (37) by treatment with methanol and hydrogen chloride.258 Glycoside 37 was then oxidized with air in the presence of a suspension of platinum oxide in aqueous sodium hydrogencarbonate solution at 60°, to afford methyl ot-L-xylo-2-hexulopyranosidonic acid (38), which, when heated in hydrochloric acid, was converted into L-ascorbic acid (1), presumably by way of L-xy/o-2-hexulosonic acid (see Scheme 5). Acid 38 has also been prepared by oxidation of 37 with nitrogen tetraoxide.259,280 Yields were not reported for this reaction sequence, and it appears to offer no potential... 

Three kinds of sugar acids can be formally obtained from the corresponding aldoses. They are aldonic acids, produced by oxidation at C-l of the aldose uronic acids, formed by oxidation of the primary alcohol group of the aldose and aldaric acids, formed by oxidation of both the aldehyde and the primary alcohol group. 

The final oxidation step of the primary alcohol at C-l in L-Srb requires acetone protection, which is carried out in a standard textbook way in the presence of an excess of sulfuric acid. The oxidation at C-l has been accomplished in a number of ways [147] it seems that nowadays aerobic oxidation in the presence of palladium or platinum is preferred. Deprotection, requiring additional sulfuric acid, affords 2KLG, which is transformed into ASA via esterification and lac-tonization. Alternatively, the diacetone derivative of 2KLG can be converted directly into ASA by treatment with HC1 in an organic solvent. 

Intramolecular cyclization of 4 forms a tetrahydroazocine ring, leading to okaramine N (15). Oxidation at C-l of 15 gives okaramine O (16), which yields okaramine A (1) through dehydration between C-l and C-2 . On the other hand, aza-Claisen rearrangement of a reverse-prenyl group in 4, 16, and 1 leads to okaramines J (11), P (17), and H (9), respectively (Fig. (5) part 2). 

Withanolides are generally polyoxygenated, a common feature of all of them being oxidation at C-l, C-22 and C-26. They may be classified into two major groups, withanolides with a 5-lactone or 5-lactol side chain (Group A) and those with a y-lactone side chain (Group B). 

The NMR spectrum of methyl kasugaminide in deuterium oxide at 100 Me is shown in Figure 3. The anomeric proton at C-l linking with methoxyl group is shown as a doublet at 4.57 p.p.m. indicating one proton at C-2. The weak coupling, 1.6 c.p.s., is possible between protons in cis relation (28) or in equatorial-equatorial relation (6) at C-l and C-2 of the six-membered ring. 

Now that the allylic oxidation problem has been solved adequately, the next task includes the introduction of the epoxide at C-l and C-2. When a solution of 31 and pyridinium para-tolu-enesulfonate in chlorobenzene is heated to 135°C, the anomeric methoxy group at C-l 1 is eliminated to give intermediate 9 in 80% yield. After some careful experimentation, it was found that epoxy ketone 7 forms smoothly when enone 9 is treated with triphenyl-methyl hydroperoxide and benzyltrimethylammonium isopropoxide (see Scheme 4). In this reaction, the bulky oxidant adds across the more accessible convex face of the carbon framework defined by rings A, E, and F, and leads to the formation of 7 as the only stereoisomer in a yield of 72%. 

It has been shown already that C-2 of ribose is the precursor of the methyl group, and C-l is eliminated in the biosynthesis. The following observation can be pertinent to the point. Pyrimidine (58) is very unstable and quickly decar-boxylates in aqueous solution at room temperature to give pyramine (Scheme 32).67 Thus, if a C-l -C-2 fragment of the ribose part of AIRs became attached by C-2 to C-2 of a pyrimidine, oxidation of C-l to produce a carboxylic acid function could result in its smooth elimination. 

Reaction sequence E removed an extraneous oxygen by Sml2 reduction and installed an oxygen at C(15) by enolate oxidation. The C(l) and C(15) hydroxy groups were protected as a carbonate in Step E-5. After oxidation of the terminal vinyl group, the C-ring was constructed by a Dieckmann cyclization in Step F-4. After temporary protection of the C(7) hydroxy as the MOP derivative, the (1-ketoestcr was subjected to nucleophilic decarboxylation by phenylthiolate and reprotected as the BOM ether (Steps F-5, F- 6, and F-7). 

The late functionalization included the introduction of the C(10) and C(13) oxygens, which was done by phenylselenenic anhydride oxidation of the enolate in Step 1-5 and by allylic oxidation at C(13) in Step J-l. These oxidative steps are similar to transformations in the Holton and Nicolaou syntheses. 

Z-vinyl iodide was obtained by hydroboration and protonolysis of an iodoalkyne. The two major fragments were coupled by a Suzuki reaction at Steps H-l and H-2 between a vinylborane and vinyl iodide to form the C(ll)-C(12) bond. The macrocyclization was done by an aldol addition reaction at Step H-4. The enolate of the C(2) acetate adds to the C(3) aldehyde, creating the C(2)-C(3) bond and also establishing the configuration at C(3). The final steps involve selective deprotonation and oxidation at C(5), deprotection at C(3) and C(7), and epoxidation. 

All the 7,8-secoberbines incorporate an JV-methyltetrahydroisoquinoline moiety with two or three oxygenated substituents at C-l, C-2, and C-3. The lower aromatic ring possesses four substituents in a vicinal arrangement of which two are alkoxyls and the third the berbine bridge carbon. The latter may occur in different oxidation states as an aldehyde (in 1 and 2), an alcohol (3-6, 8, 9), or a carboxylic acid (7). 

Encapsulated Cu—chlorophthalocyanines oxidize hexane at C-l using 02 and at C-2 using H202 as oxidants. The dimeric structure of copper acetate is intact when it is incorporated into the zeolite. This is a regioselective aromatic hydroxylation catalyst, which mimics the specificity of the monooxygenase enzyme tyrosinase.82,89 Zeolite NaY catalysts made with a tetranuclear Cu(II) complex were synthesized and characterized.90... 

A similar procedure was applied to the synthesis of quinazolidine 189 from precursor 188 in the total synthesis of the natural product known as ( )-quinolizidine 2071 190, an alkaloid isolated from the skin of the Madagascar mantelline frog Mantella baroni, that shows an exceptional axial stereochemistry for the ethyl group at C-l. Quinolizidine 189 was transformed into 190 by oxidation and two consecutive Wittig methylenations (Scheme 34) <1999CC2281>. 

An important point concerning the spectra in Figure 3.71 is that at intermediate doping levels three principal absorption bands can be seen, at c. l.OeV, 2.7eV and 3.6eV, that are not simply the superposition of the as-grown and neutral polymer absorptions. The authors interpreted this observation in terms of the homogeneous doping of the film throughout its bulk, not just the oxidation of the surface layer or the layer next to the electrode. 

Second, metabolism of 6-fluoroBP by rat liver microsomes yields the same BP quinones obtained in the metabolism of BP (23). This suggests that these products are formed by an initial attack of a nucleophilic oxygen atom at C-6 in the 6-fluoroBP radical cation with displacement of the fluoro atom. In fact, when 6-fluoroBP is treated with the one-electron oxidant Mn(0Ac)3, the major products obtained are 6-acetoxyBP and a mixture of 1,6- and 3,6-diacetoxyBP (15), indicating that reaction occurs via an initial attack of acetate ion at C-6 of the 6-fluoroBP radical cation. On the other hand electrophilic substitution of 6-fluoroBP with bromine or deuterium ion shows no displacement of fluorine at C-6, although in both cases substitution occurs at C-l and/or C-3. These results indicate that... 

The carboxylate group of pyruvate, being the most oxidized, is called C-l, and the CH3 group is called C-3. The carboxylate group of pyruvate comes from the aldehyde of G3P, so C-4 and C-3 of glucose end up at C-l of pyruvate. There is an easy way to remember which carbons of glucose end up on the same carbon of pyruvate—the numbers of the equivalent carbons sum to 7. 

---