Rectus

If the order of decreasing precedence of the three highest ranked substituents appears in a clockwise sense the absolute configuration is R (Latin rectus... 

If the observed order of priority of the remaining three functions (a > 6 > c) is in a clockwise direction, the absolute configuration is designated R (rectus or right) if counterclockwise, the configuration is S (sinister or left). The concepts of stereochemistry and chiraUty have been extensively discussed and reviewed (27—29). 

The enzyme-catalyzed interconversion of acetaldehyde and ethanol serves to illustrate a second important feature of prochiral relationships, that ofprochiral faces. Addition of a fourth ligand, different from the three already present, to the carbonyl carbon of acetaldehyde will produce a chiral molecule. The original molecule presents to the approaching reagent two faces which bear a mirror-image relationship to one another and are therefore enantiotopic. The two faces may be classified as re (from rectus) or si (from sinister), according to the sequence rule. If the substituents viewed from a particular face appear clockwise in order of decreasing priority, then that face is re if coimter-clockwise, then si. The re and si faces of acetaldehyde are shown below. 

If the order of decreasing precedence of the three highest ranked substituents appears in a clockwise sense, the absolute configuration is R (Latin rectus, "right," "correct"). If the order of decreasing precedence is counterclockwise, the absolute configuration is S (Latin sinister, "left"). 

Figure 2. Potency of anatoxin-a analogs to induce contracture in frog rectus abdominis muscle. The data from two experiments are combined in this figure. In one, anatoxinmethylester was found to be equipo-tent with carbamylcholine. In the other, the anatoxin isomers were assayed against ACh [after cholinesterse inhibition by diisopropylfluoro-phosphate (DFP) followed by washing of the preparation] (19). Maximal contracture was measured by depolarization with KCl at the end of each experiment.

Until the recent development of appropriate HPLC techniques capable of detecting pmol amounts (see Flentge et al. 1997) ACh could only be measured chemically by relatively lengthy and expensive procedures (e.g. gas chromotography), which were not always very sensitive, or by bioassays. Although the latter, using muscle preparations that responded to ACh, such as the dorsal muscle of the leech, the rectus abdominus of the frog or certain clam hearts, were reasonably sensitive they were tiresome and not easily mastered. Thus studies on the release and turnover of ACh have not been as easy as for the monoamines. 

Fig. 16 Contours of fluorescent intensity in frozen sections of the rabbit eye following 15 pL injection of marker solution in the central vitreous cavity injection was conducted through the superior rectus muscle 15 hours following injection of 0.2% sodium fluorescein 14 days following injection of 0.1% FITC-dextran, molecular weight 66,000. (From Ref. 230.)... 

FIGURE 1.2 (Upper) Concentration-response relationship for the action of acetylcholine in causing contraction of the frog rectus abdominis muscle. The curve has been drawn using Eq. (1.4). (Lower) Hill plots for the action of acetylcholine on frog ventricle (curve I) and rectus abdominis (curve II). (From Clark, A. J., J. Physiol., 61, 530-547, 1926.)... 

Reumycin and xanthothricin were isolated from Actinomyces rectus bruneus and are useful as antitumor antibiotics. Methylation of reumycin resulted in the formation of the antibiotics, fervenulin, toxoflavine, and 7-methoxyreumycin. A review on their effects on an electron transport mechanism in animal and yeast cells was published in 1975 by Russian authors (75MI1, 75MI2). 

Optical compensation for polymers with chiral monomeric units may also occur when the racemic polymer consists of crystallites, each composed only of the rectus chains or only of the sinister polymer chains, and a same amount of optical antipode crystallites is present. This intercrystallite optical compensation211 has been found, for instance, in isotactic poly(propylene sulfide),212 poly ((3 -methy lpropiol ac (one),213 and poly(isopropylethylene oxide),214 where isochiral 2/1 helical chains are included in orthorhombic unit cells according to the space group P2 2 2. ... 

Originating from the Latin word rectus, which means right in English, t Originating from the Latin word sinister, which means left in English. 

Frog rectus abdominis Membrane depolarization Decamethonium iodide (not a receptor-mediated activity) Bums and Paton, 1951... 

The cholinesterase-inhibiting activity of the phosphorofluoridates was compared quantitatively with that of eserine sulphate thus. To 0-2 ml. of heparinized human plasma was added 05 ml. of a solution containing either eserine or the phosphorofluoridate in varying concentrations then the mixture was kept at room temperature for 10 min. before 1 /tg. of acetylcholine in 1 c.c. saline solution was added. After 5 min. at room temperature, the mixture was made up to 10 ml. with frog saline containing eserine 1/100,000, which at once stopped the action of any cholinesterase not yet inactivated. The solution was then assayed for acetylcholine on the frog rectus-muscle preparation. 

Molecules at a chiral centre can be labelled according to the direction in which groups of increasing molecular weight are organized around the centre rectus and sinister, abbreviated to R and S, depending on whether the direction of increment is clockwise or anti-clockwise, respectively. 

Secondly, we have labeled one of the substituted methanes 5-fluorochloro bromomethane and the other f -fluorochlorobromomethane. S (sinister, left) and R (rectus, right) are labels that are useful in designating the absolute configuration of chiral molecules in space. The rules for assigning S stereochemistry in one case and R stereochemistry in the other are somewhat complex but it doesn t matter, so never mind. The point is that we have a way of talking about the two possibilities. 

A muscle consists of groups of muscle bundles that join into a tendon at each end. The muscle bundles in the quadriceps are the vastus medialis, rectus femoris, vastus inter-medialis and vastus lateralis. Each bundle is separately wrapped in a sheath of connective tissue. Each muscle is composed of many fibres, packaged into bundles of about... 

We then consider the descending sequence and decide whether this is clockwise or anticlockwise the face that provides a clockwise sequence is then labelled Re and the face that provides an anticlockwise sequence is labelled Si. These are simply variants on R and S, in fact the first two letters of rectus and sinister. 

This stereochemical term (short for the Latin word rectus) is the designation for a stereoheterotopic face of a trigonal atom whose ligands appear in a clockwise sense in the order of the Cahn-Ingold-Prelog scheme when viewed from that side of the face. 

For persistent VI nerve palsy of 1 month or longer duration 1.25 to 2.5 units in the medial rectus muscle. 

---