Sydowic acid

Synthesis ofNonracemic Sydowic Acid 1.3 3.5 Synthesis of Racemic Gephyrotoxin-223AB... 

Sydowic acid (100) was prepared as outlined in Scheme 10. ° The crucial transformation of ketone (101) to cafbinol (102) was accomplished by stereoselective 1,2-addition of trimethylaluminum, which afforded superior facial selectivity for the re-face compared to Grignard reagents. In contrast, methyltri-chlorotitanium addition resulted in a 5i -face stereoselectivity. 

When Rao6 wanted to make sydowic acid 16, a sesquiterpene from Aspergillus sydowi, he chose to disconnect the ether first and to make the triol 17 by addition of three methyl groups to the keto-ester 18. This is clearly a Friedel-Crafts product but how are we to get the correct position on the aromatic ring ... 

Furukawa Y, Inubushi K (2002) Feasible suppression technique of methane emission from paddy soil by iron amendment. Nutr Cycl Agroecosyst 64 193-201 Fuseler K, Krekeler D, Sydow U, Cypionka H (1996) A common pathway of sulfide oxidation by sulfate-reducing bacteria. FEMS Microbiol Lett 144 129-134 Galushko AS, Schink B (2000) Oxidation of acetate through reactions of the citric acid cycle by Geobacter sulfurreducens in pure culture and in syntrophic coculture. Arch Microbiol 174 314-321... 

Two orthorhombic chain-packing subcells with parallel chain planes, 0 and 0, have been found. A branched fatty acid, 2-methyl-2-ethyl-icosanoic acid, exhibits 0 (von Sydow, 1959), and the dimensions are a = 8.15 A, b = 9.22 A, c = 2.55 A. The cross-section area per chain is... 

The most complete investigation of the polymorphism of normal fatty acids in the interval C12-C29 was reported by Stenhagen and von Sydow (1953). Their results can be summarized by the following schematic phase relationships ... 

The crystal structure of the A -form of penta-decanoic acid (von Sydow, 1954) is quite similar to the A-form and the form A-super. It has the same triclinic chain packing (thus these forms can be called )8-forms). The angle of tilt is between 66 and 71° which is in agreement with that of the A-form (67°). An interesting difference, however, is that the A -form is the usual lipid bilayer structure. 

The crystal structure of the B-form of stearic acid (von Sydow, 1955) is shown in Fig. 8.27. The molecules are arranged in an orthorhombic chainpacking structure, in bilayers. The orientation of the chain-packing subcell in relation to the methyl end group planes is Oi (101) (see Section 8.1). A modified B-form was observed in 11-bromoun-decanoic acid (Larsson, 1963a) which was termed Bi. It is isomorphous with the B-form according to X-ray diffraction data, but the OH-out-of-plane vibration in the infrared absorption spectra is different. A new form of stearic acid (Holland and Nielsen, 1963), described according to infrared absorption data, appears to be the same form as Bi in 11-bromoundecanoic acid. As the first crystal... 

Figure 8.26 Structure of the lauric acid crystal form A-super and the relations with the A-form, after von Sydow (1956) and Lomer (1965). If the structure unit is equivalent to the two molecules denoted 1 and 2, the crystal structure of the A-form is obtained.

Figure 8.27 The projection of the B-form of stearic acid along the shortest axis (von Sydow, 1954).

Figure 8.28 The structure of the carboxyl group region in the B-form of stearic acid as seen along the c-axis (Larsson and von Sydow, 1956).

The crystal structure of the C-form of lauric acid was the first fatty acid structure determined (Vand et al., 1951). The structure is of the usual bilayer type with the chains arranged to the orthorhombic chain packing. The structure of the C -form of undecanoic acid has also been determined (Fig. 8.30) (von Sydow, 1956b). It is strictly isostructural with that of the C-form. The molecular arrangement in the bilayer is thus the same with the end group plane related to the chain-packing subcell according to O i (021). 

Figure 8.30 The projection of the C -form of undecanoic acid along the shortest unit cell axis (von Sydow, 1956).

Methyl esters of saturated fatty acids show one stable crystal form. It was originally termed but according to the nomenclature used here it is a )8 -form. The crystal structure of this form in methyl stearate (Aleby and von Sydow, 1960) is shown in Fig. 8.36. Although the forces between the polar groups must be very weak in an ester the molecules are arranged head-to-head in bilayers. The chain packing is the... 

The progression bands were not only valuable for identification of homologues, but also for distinguishing different crystal forms of fatty acids. The intensity of the wagging progression bands is dependent on the crystal structure. Nujol spectra of the A, B and C forms of two odd-numbered acids (chain length C15, C17) and of the A, B and C forms of one even-numbered acid (Cie) have been published (von Sydow, 1955). The spectral features of the different crystal forms were studied using polarized spectra and variable temperature techniques (Susi and Smith, 1960 Chapman, 1962). 

Palmitic acid ( Ci HsaOs ) + Isoniargarinic acid von Sydow, 1954... 

Palmitic acid ( C, von Sydow, 1954 32O2 ) + Isoeicosanoic acid ( C2oHl4-0 2 )... 

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