Extensive chromatography

A later report has demonstrated that the initial product urorosein (144) is unstable and decomposes in solution into a variety of products. After extensive chromatography and characterization, it was concluded that several of the decomposition... 

Attempts have been made to solve the problem of selective substitution in sucrose octaacetate. Adsorption of the latter onto alumina for 46 hours gave a complex mixture from which, after extensive chromatography, were isolated the 2,3,4,6,l, 3, 4 -heptaacetate in 9% yield,11 the 2,3,6,l, 3, 4, 6 -heptaacetate in 2.7% yield,117 and the 2,3,4,6,1, 3, 6 -heptaacetate in 6% yield.117 Although selective deacylation of the octaacetate apparently occurs at secondary positions, as well as at 0-6, it is likely that heptaacetates containing 4- and 4 -OH groups... 

Ketone 16 can be prepared from glucose in 6 steps without extensive chromatography purification (Scheme 10.5).78. V-Aryl-substituted oxazolidinone-containing ketone 18 can be synthesized... 

Recently, a convenient preparation of an analytical construct of type 182 (Fig. 17) has been reported. The synthesis of 182 is possible without a need for extensive chromatography. Furthermore, the deuterium mass tag can be incorporated vhth D2O in a cost-effective manner [204]. 

From Zizyphus sativa (Rhamnaceae), discarine-related 13-membered cyclopeptide alkaloids, sativanines C (1) (14), D (57), E (2), F (3) (15-17), and G (4) (18) have been isolated. Ilie bark of Z. sativa is used to heal ulcers and wounds. Extensive chromatography of the crude bases furnished a further, previously unknown, 13-membered cyclopeptide alkaloid sativan-ine H (5) (79). Sativanine K (6) has been obtained from the powdered bark of Z. sativa. This is the first 13-membered cyclopeptide alkaloid to contain an JV-formyl group as well as a short side chain (20). A new, minor... 

Reduction of the lactone 137 to the corresponding lactol 138 necessitated use of DIBAL quenching the reaction with methanol followed by workup with aqueous potassium sodium tartarate furnished the product as a clear viscous oil that solidified on standing to a white solid. The anomeric hydroxyl group was conveniently protected by the formation of terf-butyldimethylsilyl ether by treatment with rert-butyldimeth-ylsilyl chloride, imidazole, and A,A-dimethylaminopyridine. Further activation of the anomeric position in compound 139 with trimethylsilyl bronfide followed by treatment with l-t-butyldimethysiloxy-3-butyne and n-butyUithium yielded a transicis mixture (1 1) (140) that was used without further purification. Reaction of compound 140 with tetrabutylammonium fluoride led to deprotection of the hydroxy functionality. The resulting transicis mixture of the alkynols was subjected to extensive chromatography and repeated crystallization to obtain a tran -alcohol (141) as a white crystalline solid. Further elaboration to 131 was carried out by appropriate modifications of a literature procedure. ... 

In the early part of this century, the first procedures for the isolation of carotenoids and, subsequently, the first methods for systematic structure elucidation were developed. The initial synthetic procedures were limited to simple chemical modifications of the isolated carotenoids. These methods gradually lost their importance for preparative purpose because of the poor yields of such chemical transformations carried out on a chemically labile C40-polyene and the necessity to purify the products by extensive chromatography. 

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