Polycavernosides A and B are glycosidic macrolide natural products isolated as the toxins causing fatal human poisoning by the edible red alga Gracilaria edulis (Polycavernosa tsudai). Total synthesis of polycavernosides A and B has been achieved via a convergent approach. The synthesis of the macrolactone core structure is highlighted by the catalytic asymmetric syntheses of the two key fragments using hetero-Diels-Alder reaction and Kiyooka aldol reaction as the key steps, their union through Suzuki-Miyaura coupling, and Keck macrolactonization. Finally, glycosylation with the l-fucosyl-d-xylose unit and construction of the polyene side chain through Stille coupling completed the total synthesis of polycavernosides A and B.

An isotope dilution method of [2H5]phenylalanine (Phe) and [2H2]tyrosine (Tyr) was used to determine the effects of metabolisable energy (ME) intake and cold exposure on plasma Phe and Tyr turnover rates in sheep. Whole body protein synthesis (WBPS) was calculated with the [2H5]Phe model. Eight adult sheep were assigned to two dietary treatments receiving the same amount of crude protein and either 515 or 828 kJ x kg BW(-0.75) x d(-1) of ME (Me-ME diet and Hi-ME diet, respectively) with a crossover design for two 28 d periods. The sheep were exposed from a thermoneutral environment (23 +/- 1 degrees C) to a cold environment (2 +/- 1 to 4 +/- 1 degrees C) for 6 d for each dietary treatment. The primed-continuous infusion method of isotope dilution was conducted in both environmental temperatures. Plasma Phe turnover rate (PheTR) tended to be greater and plasma Tyr turnover rate (TyrTR) was greater (p = 0.03) for the Hi-ME diet compared with the Me-ME diet. Plasma PheTR increased (p = 0.04) and plasma TyrTR tended to increase during cold exposure. Whole body protein synthesis tended to be greater for the Hi-ME diet compared with the Me-ME diet and increased (p = 0.03) during cold exposure compared to the thermoneutral environment, but no interaction was detected. It was concluded that in sheep, plasma PheTR and WBPS (as determined by the [2H5]Phe model) tended to be influenced by and plasma TyrTR was influenced by ME intake. Further, plasma PheTR and WBPS increased and plasma TyrTR tended to increase during cold exposure.