Quercitols

Samen-haar, n. (Bot.) seed hair, coma, -hefe, /. seed yeaat. -keim, m. germ, embryo, -kem, m. seed kernel (Bot.) endosperm Physiol.) spermatic nucleus, -lappen, m. seed lobe, cotyledon, -ol, n. seed oil. -pflan-zen, /.pi. seed plants, Spermatophyta. -probe, /. seed test or sample, -saift, m. seminal fluid, -staub, m. pollen, -tierchen, n. sp< rmatozoon. -zelle, /. seminal cell, spertpatozoon. -zucker, m. quercitol, quer-cite. ... 

The deoxyinositols (quercitols, cyclohexanepentols) are useful model compounds which display many of the physical and chemical properties of true deoxy sugars. Although (-b)-proto-quercitol, the best known isomer, was isolated from nature 118 years ago, no synthesis has been reported up until now. The synthesis here described is actually that of the (-)-enantiomer, starting with (-)-inositol however, identical procedures applied to the readily available ( + ) or dl-inositol would give (- -) or DL-proto-quercitol, respectively. The natural occurence of, )-proto-quercitol has... 

Synthesis of Deoxyinosamines from vibo-Quercitol. As yet, the quercitols have rarely been used as synthetic starting materials. Recently, however, Suami and Yabe (42) have reported clever syntheses of two (acetylated) deoxyinosamines (8 and 9, Y= NHAc) and one (acety-lated) deoxyinosadiamine (10, Y = NHAc) from racemic vibo-quercitol... 

The vibo or dl (124/35) quercitol (4) needed for the synthesis was prepared from rat/o-inositol (2) via the bromoquercitol (3) according to the method of McCasland and Horswill, (28). By acetonation, acetylation, deacetonation, and equatorial mesylation the mesyloxy derivative... 

Natural Occurrence of ( — )-proto-Quercitol. Although the dextrorotatory form (12) of proto-quercitol was discovered in acorns more than a century ago by Braconnot (5), who at first thought that it was lactose, the levorotatory form (13) remained unknown until 1961. In that year, Plouvier isolated it from leaves of the tree Eucalyptus populnea the yield was 0.55% (36). The optical rotation of the new compound was equal and opposite to that of the dextro enantiomer, and it was identical to the latter in its crystal form, melting point, solubilities, molecular formula and infrared spectrum. 

Plouvier then prepared the previously unknown racemic form of proto-quercitol by mixing equal weights of the two enantiomers. The melting point (237°C.) of the mixture was not depressed, and its (presumably solid state) infrared spectrum reportedly (36) was identical with that of either active form. It thus appears that DL-proto-quercitol exists as a solid solution, not a racemic compound or conglomerate. 

The discoverer of levorotatory proto-quercitol unfortunately described it (36) as L-quercitol. The capital letter l should of course be understood to designate configuration, not rotation. And according to one widely accepted convention (18,19), the quercitol stereosiomer which has the configuration 13 would be designated V , not l . (See formulas 12 and 13.) The name quercitol is now used in a generic sense (cyclo-hexanepentol), so that there are actually six diastereomers to which the name L-quercitol might apply. 

According to the modified Maquenne system (18,19,31) used in this chapter, the diastereomeric configuration of any cyclitol is expressed by a fraction, and position-numbering, if otherwise equivocal, is so assigned that the numerator will have the lowest possible numbers. For example, proto-quercitol (12 or 13) is designated (134/25,), not (14/ 235) or (25/134). 

The Synthesis of (— -proto-Quercitol, Although proto-quercitol (dextro) was discovered in 1849 ( 5), its cyclohexanepentol structure was not established until 1885 (13), and its configuration not until 1932. (38). The synthesis of this well-known cyclitol has been a difficult problem, since it appears that nearly every synthetic reaction commonly employed for other cyclitols would lead stereospecifically to the wrong product. 

It was not until 1966 that the synthesis of proto-quercitol (levo) was finally accomplished (30) by indirect removal of the position 2 hydroxyl group in (—) -inositol (14). 

The pure, crystalline (— )-proto-quercitol (13) which was isolated had an infrared spectrum identical with that of authentic ( + )-proto-quercitol, and its optical rotation was equal and opposite. Further characterization and preparation of the racemic form, by mixing the enantiomers, is described elsewhere (30). 

The identical synthetic procedures applied to ( + )-inositol or dl-inositol should lead to ( + )-proto-quercitol and DL-proto-quercitol, respectively. Since the total synthesis of DL-inositol had previously been reported (33), the new syntheses of the various forms of proto-quercitol are total, with the possible exception of the step for resolution of DL-inositol, which so far has been accomplished only by a microbiological method (43). 

In early experiments, the pentamethyl ether (18) was treated with phosphorus pentachloride in the hope of obtaining a chloropentol reducible to ( — )-proto-quercitol. (Allowing for the benzoyl migration, the expected product would have been (— )-uibo-quercitol (11).) Surprisingly, the quercitol actually obtained after demethylation and dehalogena-tion was neither of these but still another previously known isomer, meso-scyllo-quercitol (24) (27). 

Early in 1961, the first successful use of NMR for the assignment (22) of configuration to a quercitol (26) was accomplished indirectly, by analysis of the spectrum of its 6-bromo derivative. The spectrum of this bromoquercitol (25 or 28) fortunately contained a well-resolved AB... 

In the past, periodate titrations have been of limited value for establishing the structure of quercitols or cyclohexanetetrols. The former show overoxidation, because of the fact that malonaldehyde is formed, and this compound undergoes further oxidation. Some isomers of the tetrols... 

It is now reported by P. Szabo that the quercitols can be titrated with completely normal results, by using suitable experimental conditions, and especially low temperature and low pH, for the titrations (40,41). This method might also be applicable to the estimation of the tetrols. 

Figure 2. Proton magnetic resonance spectra at 14.1, 23.5, and 51.7 kilogauss (60, 100 and 220 MHz.) of (H-j-proto-quercitol in deuterium oxide.

Figure 3. Oxidation of (1 i.)-l,2,4/3,5-cyclohexanepentol (curve A minutes Curve C hours) and of (+)-quercitol (curve B minutes curve D hours) with sodium metaperiodate (c.f. Table I).

Thus, as far as ( + )-quercitol is concerned (Figure 5), the time curves show that a small quantity of malonaldehyde is liberated at the beginning... 

As ( + )-quercitol (26) possesses only one pair of cis-vicinal hydroxyl... 

No hypotheses can be advanced for the sequences involved in the oxidation of cyclohexanepentols which react even more slowly with periodate than does (+)-quercitol. For instance, when the all-trans l 3, 5/2, 4-cyclohexanepentol (33) is oxidized (Figure 6), production of malonaldehyde starts very early and the time curve of periodate reduction indicates a very complex reaction. Nor is it possible to analyze satisfactorily the curves obtained with (1 l)-1, 2, 4/3, 5-cyclohexane-pentol (34) or with dl-1, 2, 3, 4/5-cyclohexanepentol (35) [this is the configuration predicted for the (1 D)-entantiomorph (41)]. 

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