An isomer is a molecule with the same molecular formula as another molecule, but with a different chemical structure. That is, isomers contain the number of atoms of each element. Isomers do not necessarily share similar properties, unless they have the functional groups. There are two forms of isomerism, structural isomerism and stereoisomerism. In structural isomers, sometimes referred to as constitutional isomers, the atoms, Structural isomers have different IUPAC names and may or may not belong to the same functional group. For example, two position isomers would be 2-fluoropropane and 1-fluoropropane, illustrated on the side of the diagram above. In skeletal isomers the main chain is different between the two isomers. This type of isomerism is most identifiable in secondary and tertiary alcohol isomers, tautomers are structural isomers that spontaneously interconvert with each other, even when pure. They have different chemical properties and, as a consequence, distinct reactions characteristic to each form are observed, if the interconversion reaction is fast enough, tautomers cannot be isolated from each other.
An example is when they differ by the position of a proton, such as in keto/enol tautomerism, there is, another isomer of C3H8O that has significantly different properties, methoxyethane. Unlike the isomers of propanol, methoxyethane has an oxygen connected to two carbons rather than to one carbon and one hydrogen. Methoxyethane is an ether, not an alcohol, because it lacks a hydroxyl group and propyne are examples of isomers containing different bond types. Propadiene contains two double bonds, whereas propyne contains one triple bond, in stereoisomers the bond structure is the same, but the geometrical positioning of atoms and functional groups in space differs. This class includes enantiomers which are non-superposable mirror-images of each other, and diastereomers, enantiomers always contain chiral centers and diastereomers often do, but there are some diastereomers that neither are chiral nor contain chiral centers. Another type of isomer, conformational isomers, may be rotamers, for example, ortho- position-locked biphenyl systems have enantiomers. E/Z isomers, which have restricted rotation at a bond, are configurational isomers.
They are classified as diastereomers, whether or not they contain any chiral centers, e/Z notation depicts absolute stereochemistry, which is an unambiguous descriptor based on CIP priorities. Cis–trans isomers are used to describe any molecules with restricted rotation in the molecule, for molecules with C=C double bonds, these descriptors describe relative stereochemistry only based on group bulkiness or principal carbon chain, and so can be ambiguous
Retroprogesterone, known as 9β, 10α-progesterone or as 9β, 10α-pregn-4-ene-3, 20-dione, is a synthetic steroid and stereoisomer of the natural progestogen, progesterone. It is the parent compound of a group of progestins consisting of dydrogesterone and trengestone, retroprogesterone itself binds with high affinity to the progesterone receptor as well. Ro 6-3129 is a retroprogesterone derivative progestin that was never marketed
International Chemical Identifier
Initially developed by IUPAC and NIST from 2000 to 2005, the format and algorithms are non-proprietary. The continuing development of the standard has supported since 2010 by the not-for-profit InChI Trust. The current version is 1.04 and was released in September 2011, prior to 1.04, the software was freely available under the open source LGPL license, but it now uses a custom license called IUPAC-InChI Trust License. Not all layers have to be provided, for instance, the layer can be omitted if that type of information is not relevant to the particular application. InChIs can thus be seen as akin to a general and extremely formalized version of IUPAC names and they can express more information than the simpler SMILES notation and differ in that every structure has a unique InChI string, which is important in database applications. Information about the 3-dimensional coordinates of atoms is not represented in InChI, the InChI algorithm converts input structural information into a unique InChI identifier in a three-step process, normalization and serialization.
The InChIKey, sometimes referred to as a hashed InChI, is a fixed length condensed digital representation of the InChI that is not human-understandable. The InChIKey specification was released in September 2007 in order to facilitate web searches for chemical compounds and it should be noted that, unlike the InChI, the InChIKey is not unique, though collisions can be calculated to be very rare, they happen. In January 2009 the final 1.02 version of the InChI software was released and this provided a means to generate so called standard InChI, which does not allow for user selectable options in dealing with the stereochemistry and tautomeric layers of the InChI string. The standard InChIKey is the hashed version of the standard InChI string, the standard InChI will simplify comparison of InChI strings and keys generated by different groups, and subsequently accessed via diverse sources such as databases and web resources. Every InChI starts with the string InChI= followed by the version number and this is followed by the letter S for standard InChIs.
The remaining information is structured as a sequence of layers and sub-layers, the layers and sub-layers are separated by the delimiter / and start with a characteristic prefix letter. The six layers with important sublayers are, Main layer Chemical formula and this is the only sublayer that must occur in every InChI. The atoms in the formula are numbered in sequence, this sublayer describes which atoms are connected by bonds to which other ones. Describes how many hydrogen atoms are connected to each of the other atoms, the condensed,27 character standard InChIKey is a hashed version of the full standard InChI, designed to allow for easy web searches of chemical compounds. Most chemical structures on the Web up to 2007 have been represented as GIF files, the full InChI turned out to be too lengthy for easy searching, and therefore the InChIKey was developed. With all databases currently having below 50 million structures, such duplication appears unlikely at present, a recent study more extensively studies the collision rate finding that the experimental collision rate is in agreement with the theoretical expectations.
Example, Morphine has the structure shown on the right, as the InChI cannot be reconstructed from the InChIKey, an InChIKey always needs to be linked to the original InChI to get back to the original structure
Lynestrenol, known as 17α-ethynyl-3-desoxy-19-nortestosterone or 17α-ethynylestr-4-en-17β-ol, is a steroidal progestin of the 19-nortestosterone group. It is used as a contraceptive and in the treatment of gynecological disorders. Lynestrenol itself does not bind to the receptor and is inactive as a progestogen. It is a prodrug, and upon oral administration, is rapidly and almost completely converted into norethisterone, no other metabolites besides norethisterone are formed from lynestrenol. As such, its activity is essentially identical to that of norethisterone. The conversion of lynestrenol into norethisterone is catalyzed by CYP2C9, CYP2C19 and it appears that lynestrenol first undergoes hydroxylation of the C3 position, forming etynodiol as an intermediate, followed by oxygenation of the hydroxyl group to form norethisterone. The peak blood are reached within 2 to 4 hours after oral administration and its metabolites are predominantly excreted in the urine, less through feces, active metabolite norethisterone elimination half-life being 16 to 17 hours.
Lynestrenol is a derivative of 19-nortestosterone, and is a member of the estrane subgroup and it differs from norethisterone and etynodiol only by the lack of a ketone group and hydroxyl group at the C3 position, respectively. In another approach to analogs, nortestosterone is first converted to the dithioketal by treatment with dithioglycol in the presence of boron trifluoride, treatment of this derivative with sodium in liquid ammonia affords the 3-desoxy analog. Oxidation by means of Jones reagent followed by ethynylation of the 17-ketone leads to the orally active progestin, lynestrenol was developed by the Dutch pharmaceutical company Organon in the late 1950s. It received a Dutch patent for lynestrenol in 1957, and lynestrenol subsequently became a component of Lyndiol, around this time, pre- and post-marketing clinical trials of lynestrenol were conducted, and in 1965, a study consisting of 200 Dutch women was published. Lynestrenol was approved, in the United Kingdom, in combination with mestranol in 1963 and it has been used mainly in Europe and is marketed in many other countries throughout the world.
The drug was never marketed in the United States