Polymeric Proanthocyanidins from Psidium auaiava

From the aqueous acetone extract of the leaves of Psidium guajava L. the flavanols catechin and gallocatechin, the procyanidins B1, B2, B3 and two prodelphinidins (gallocatechin (4a+8) catechin; gallocatechin (4a+8) gallocatechin) were isolated. A more abundant proanthocyanidin polymer was also isolated, purified and its chemical constitution studied by 1 3 ~ ~ ~ ~ and phloroglucinol degradation. The mean molecular weight of the polymer was estimated to be about 9 to 10 flavan-3-01-units with a ratio of procyanidin : prodelphinidin units at 2 : 1 some of which are derivatized by gallic acid.

Little is known about the structural design of the polymeric proanthocyanidin fraction of the title plant.However, this knowledge is of importance for a better understanding of the chemical structure of the proanthocyanidins in relation to their pharmacological and microbiological effects.

Results and Discussion
The ethylacetate fraction obtained from the aqueous acetone extract of the To elucidate the structure in more detail, the polymer was subjected to mild acid catalysed scission, and the generated extender flavan carbocations were captured with phloroglucinol as described [27, 301.The reaction resulted in the cleavage of the terminal flavanoid units, which where identified as catechin (1) and gallocatechin (2).A small amount of the procyanidin dimer, epicatechin-(4P+8)-catechin (7) was also isolated from the reaction mixture, confirming the propensity of catechin as end unit.Among the monomeric phloroglucinol captured products epicatechin-(4P+2)-phloroglucinol (3), was performed on silica gel plates (Kieselgel 60 F254, 0.5 mm, Merck) using toluene-Me2C0 (7: 3) for peracetates.Optical rotation ([a]) was measured using a Perkin-Elmer polarimeter 241.

Plant material
Psidium guajava L. leaves were collected from trees grown in Sudan (0712001) and identified in comparison with authentic Psidium guajava obtained from the University of JordanlAmman.A voucher specimen is deposited at the University of Petra (no.0701).

Preparation of polymeric fraction
Preparation of the polymeric fraction was achieved and defined according the procedure described by Foo et at. [27,30].The water-phase (WP) obtained after extraction of the plant material (204 g) was fractionated by CC on Sephadex IA-20 ( 5 .5 ~ 68 cm) with MeOH-H20 1:l (20 1) until the eluent was colourless; then acetone-H20 7:3 (7 1) was used for elution to obtain the polymeric fraction (19 g).

FadiFig. 2 .
Fig. 2. Structure of the subunit products found in Psidium guajava leaves following acid-catalysis in the presence of phloroglucinol.