Macrocyclic Oligoesters Incorporating a Cyclotetrasiloxane Ring.

Macrocyclic oligoester structures based on a cyclotetrasiloxane core consisting of tricyclic (60+ atoms) and pentacycylic (130+ atoms) species were identified as the major components of a lipase-mediated transesterification reaction. Moderately hydrophobic solvents with log P values in the range of 2-3 were more suitable than those at lower or higher log P values. Temperature had little effect on total conversion and yield of the oligoester macrocycles, except when a reaction temperature of 100 °C was employed. At this temperature, the amount of the smaller macrocycle was greatly increased, but at the expense of the larger oligoester. For immobilized lipase B from Candida antarctica (N435), longer chain length esters and diols were more conducive to the synthesis of the macrocycles. Langmuir isotherms indicated that monolayers subjected to multiple compression/expansion cycles exhibited a reversible collapse mechanism different from that expected for linear polysiloxanes.

Presence of Ribeiroia ondatrae in the developing anuran limb disrupts retinoic acid levels.

The widespread reports of malformed frogs have sparked interest worldwide to try and determine the causes of such malformations. Ribeiroia ondatrae is a digenetic trematode, which has been implicated as one such cause, as this parasite encysts within the developing tadpole hind limb bud and inguinal region causing dramatic limb malformations. Currently, the mechanisms involved in parasite-induced limb deformities remain unclear. We sought to investigate whether the level of retinoic acid (RA), a morphogenetic factor known to play a critical role in limb bud formation, is altered by the presence of R. ondatrae within the infected tadpole. Alteration of RA levels within the limb bud caused by the presence of the parasite may be achieved in three ways. First, metacercariae are actively secreting RA; second, cercariae, upon entering the limb/inguinal region, may release a large amount of RA; finally, the metacercariae may induce either an increase in the synthesis or a decrease in the degradation of the host's endogenous retinoic acid levels. Here, we show through high performance liquid chromatography and mass spectrometry that limb bud tissue of Lithobates sylvaticus, which has been parasitised, contains 70% more RA compared to the unparasitised control. Furthermore, parasites that have encysted within the limb buds appear to contain substantially less RA (56%) than the free swimming cercariae (defined as the infectious stage of the parasite). Taken together, these data illustrate for the first time that encystment of R. ondatrae leads to an increase in RA levels in the tadpole limb bud and may offer insight into the mechanisms involved in parasite-induced limb deformities.