Organic synthesis

Some comments on the problems that are encountered by organic chemists who attempt the total synthesis of a molecule having several asymmetric centers. These difficulties explain the relatively slow progress of that branch of chemistry, although some of its successes merit being considered works of art.     

Recent patents on oligonucleotide synthesis and gene synthesis

Gene synthesis is an emerging field which has widespread implications in synthetic biology and molecular biology. The field is constantly evolving which has led to key advances in oligonucleotide synthesis and gene synthesis technologies, with simplicity, cost effectiveness and high throughput. The miniaturization, multiplexing, microfluidic processing and the integrated microchip engineering will drive down cost and increase productivity without compromising DNA synthesis fidelity, whereas the gigantic amount of genome information provides infinite source of DNA elements and genes as raw material for synthetic biology. This article describes some of the recent patents on oligonucleotide synthesis and gene synthesis.     

GPI-anchor synthesis

The glycosyl phosphatidylinositol (GPI) anchor of membrane proteins is widely distributed in eukaryotes and parasitic protozoa. The structure and biosynthetic pathway of its core have been elucidated and appear to be conserved in various species. Some of the genes involved in mammalian GPI-anchor biosynthesis have recently been isolated using GPI-anchor-deficient mutant cell lines and expression cloning methods. One of these genes proved to be responsible for a GPI-anchor deficiency known as paroxysmal nocturnal hemoglobinuria. Since the core of the GPI anchor is variously modified in different species and since there may be other differences between its biosynthetic pathway in parasites and their hosts, this pathway could be a target for chemotherapy. In this review, Taroh Kinoshita and Junji Takeda focus on the GPI-anchor biosynthetic pathway and the genes involved in it.     

Unprotected synthesis

Chemists at The Scripps Research Institute demonstrate that it is possible to synthesize complex natural products without the use of protecting groups.     

Lag-phase and rate of synthesis in light-mediated anthocyanin synthesis

Mustard (Sinapis alba L.) seedlings were irradiated with continuous far-red light either with or without a pretreatment with 3 or 6 h of the same far-red light, separated by a 15 h dark period. The pretreatment increases the initial rate of anthocyanin accumulation — as caused by the 2nd light treatment — at least 6-fold but leads to an earlier cessation of anthocyanin accumulation. Moreover, the pretreatment seems to shorten the apparent lag-phase of anthocyanin accumulation considerably but it does not eliminate the lag. If the pretreatment with far-red light is terminated before the seedling reaches competence (with regard to phytochrome and anthocyanin synthesis) the pretreatment has no effect on the apparent lag-phase even though the future capacity of anthocyanin biogenesis is considerably stimulated by the pretreatment. The time course of induction of anthocyanin and that of phenylalanine ammonia-lyase (PAL) (Acton et al. 1980, Fig. 1) is in line with the concept that induction of PAL by light is a prerequisite for the onset of light-mediated anthocyanin synthesis.Abbreviation PAL phenylalanine ammonia-lyase     

Enhanced sterol synthesis in concanavalin A-stimulated lymphocytes: correlation with phospholipid synthesis and DNA synthesis.

Incorporation of (14C)choline and (3H)myo-inositol into the total lipid fraction, incorporation of (14C)acetate into the sterol fraction and incorporation of (3H)thymidine into DNA were studied in human lymphocyte cultures. Concanavalin A induced an increase in the incorporation of these labels with the following features: (a) Phospholipid synthesis was increased promptly. The lag time for the increase in sterol synthesis and DNA synthesis were 5 hours and 27 hours respectively; (b) The increase in phospholipid synthesis and sterol synthesis was proportional to ConA concentration initially. Cells treated with a high concentration of ConA showed very low levels of DNA synthesis; (c) The increase in phospholipid synthesis could be abolished immediately by alpha-Methyl-Mannoside. alpha-Methyl-Mannoside blunted but did not abolish the increase in sterol synthesis. alpha-Methyl-Mannoside enhanced DNA synthesis of those cells which had been treated by a high concentration of ConA; and (d) Selective inhibition of sterol synthesis with 25-hydroxycholesterol did not prevent the increase in phospholipid synthesis, but it blocked the increase in DNA synthesis. Supplement of LDL, HDL or total lipoproteins to lymphocyte cultures was effective in preventing the inhibition of DNA synthesis by 25-hydroxy-cholesterol. These results suggest that in lymphocyte activation by ConA phospholipid synthesis, sterol synthesis and DNA synthesis were sequentially increased. The rate of cellular commitment to mitogenesis was proportional to ConA concentrations. High concentrations of ConA arrested the cell growth at a postcommitment point in the G1 phase. Enhanced phospholipid synthesis was a precommitment event. Enhanced sterol synthesis was a postcommitment event and reflected the requirement of an increased cholesterol supply for the passage of cell growth through G1.     

Glycoconjugate synthesis during early pregnancy: hyaluronate synthesis and function

The synthesis of various glycoconjugate classes by mouse uteri during the pre- and peri-implantation period has been examined using [3H]glucosamine as a metabolic precursor. A unique and dramatic (five- to sixfold) increase was observed in the synthesis of hyaluronate on the day upon which embryo implantation normally occurs. Mated, but nonpregnant mice did not display increased hyaluronate biosynthesis. In contrast to hyaluronate, the synthesis of most other types of glycoconjugates remained fairly constant during the first 5 days of pregnancy. Low (1500-5000)-molecular-weight N-linked oligosaccharides constituted the major class of oligosaccharides synthesized under all conditions. High (greater than 10,000)-molecular-weight glycoconjugates constituted the second most abundant class of glycoconjugates synthesized (20-30%). Most (85%) of the newly synthesized hyaluronate was associated with the nonepithelial cell types of the uterus. Experiments using ovariectomized mice receiving steroid hormones demonstrated that uterine hyaluronate synthesis was induced preferentially by an artificial decidual stimulus and implicated stromal cells as the site of hyaluronate synthesis. In addition, it was demonstrated that tissue culture plates coated with hyaluronate, but not other polysaccharides, support attachment and spreading of a large fraction (60 to 70%) of embryos cultured in serum-free medium. Collectively, these studies indicate that increased hyaluronate biosynthesis accompanies decidual responses in the endometrium and may promote embryo implantation following initial penetration of the uterine epithelium.