The structure of phragmalin: an X-ray analysis of phragmalin iodoacetate

Abstract

The molecular structure of phragmalin, the methyl ester of a C2sH34011 terpenoid constituent of the tree Entandrophragma caudatum (a member of the Meliaceae family), has been determined by means of an X-ray study of phragmalin iodoacetate. The crystals of phragmalin iodoacetate are orthorhombic with space group P212121 and 4 molecules in the unit cell of dimensions a= 15.70, b= 19"59 and c= 11.25/~. An orthoester linkage spanning a cyclohexane ring results in an atomic arrangement which is unique for this class of natural product.

Structural Studies on Three Plant Diterpenoids from Leonotis nepetaefolia

“…The δ-lactone ring (C) conformation is best described by an intermediate between sofa and half-chair conformation. The torsion angles of the δ-lactone ring are in good agreement with the reported values (COETZER et al, 1971;BAKHARI et al,1998). Long range conformational transmission effects, intra-intermolecular and crystal packing effects might be important in determining the exact conformation of each ring (THOMAS, 1985).…”

Meliaceous Limonoids: Chemistry and Biological Activities

“…Up to now, four subtypes of phragmalin orthoesters have been reported, which were classified into 1,8,9- (−- 910 ), 8,9,11- ( 911 – 916 ), 8,9,14- ( 917 – 930 ), and 8,9,30-phragmalin orthoesters ( 931 – 962 ) according to the position of the ortho -acetate group. The structure of phragmalin ( 846 ) was proposed on the basis of chemical and spectroscopic evidence and then determined by means of an X-ray study of its iodoacetate . The distribution of phragmalins and mexicanolides in the stem barks, fruits, and seeds of the Chinese mangrove plant Xylocarpus granatum was discussed, and the conclusion was reached that the high concentration of phragmalin orthoesters in the stem barks of Xylocarpus plants might serve as an important chemical defense aginst invasion by pests or microorganisms .…”

Semisynthesis of Libiguin A and Its Analogues by Trans-Lactonization of Phragmalin

“…Although synthetic studies of several structural types of limonoids have been performed, to the best of our knowledge no synthetic or semisynthetic approach for constructing the libiguin scaffold has been reported to date. As a potential starting material for the semisynthesis, we proposed phragmalin, a limonoid that is present in large quantities in some species of the Meliaceae family. , In the commercially cultivated species Chukrasia tabularis, which can be grown in a sustainable manner, phragmalin may be isolated in kilogram quantities per ton of plant tissue . The major differences between phragmalin and libiguins are the location of the lactone ring, which is formed with the 17-oxy functionality in phragmalin and with the 30-oxy functionality in the libiguins.…”