Homochirality biological

Experimental Approaches to the Understanding of the Origins of Biological Homochirality Using Asymmetric Autocatalysis... 

Spontaneous absolute asymmetric synthesis, i.e., the formation of an optically active compound without the use of chiral materials, has been proposed as one of the origins of biological homochirality in nature [14,15]. Spontaneous... 

The author originally reviewed three important aspects of semiochemical research that has been discussed in Volume 9. They are as follows (1) determination of structure including the absolute configuration of bioactive natural products, (2) problems of biological homochirality, and (3) study of structure—activity relationships to invent mimics of bioactive small molecules so as to utilize them as pesticides or medicinals. 

As we read more about disubstituted glycines, we learned that some such species are delivered by carbonaceous chondritic meteorites, and with partial enantioexcesses. This information offered a clue as to how biologic homochirality could have originated on earth (see below). 

A phenomenon that may be related to the origin of biological homochirality was recently reported by Cooks and coworkers 39 Serine sublimes with spontaneous chiral amplification. Sublimation of near racemic sample of serine 55 (Figure 9) yields a sublimate that is enriched in the major enantiomer. The chiral purity maximizes at 190-210 °C, and then falls as thermolysis becomes favorable. This simple one-step sublimation may represent a possible mechanism for the chiral amplification step to explain the origin of biological homochirality. 

Figure 9 Structures of compounds in connection with biological homochirality (1).

Second, problems related to biological homochirality have been discussed to contemplate its origin and also to see exceptions to the homochirality principle. The presence and roles of D-amino acids in organisms as well as the presence of stereochemically heterogeneous compounds have been illustrated with examples. 

Chiral crystals provide an environment for the discrimination of chiral molecules, so their possible roles in the origin of biological homochirality have been discussed... 

The origin of life on Earth is one of the greatest and most fascinating puzzles of mankind. Scientists generally assume that it evolved in a stepwise process with increasing complexity, but the many questions of how exactly that happened remain essentially unanswered (1). One part of this big puzzle that is of particular interest for many chemists is the origin of biological homochirality. 

The aim of this chapter is to give an overview on this topic by discussing a selection of observations, experimental results and scenarios, especially those related to amino acids. This emphasis allows the presentation of different models based on the same substance class in a closer context and also discussion of some more recent works. A more detailed survey of other models for the origin of biological homochirality can be found in review articles (2-5). 

Some pieces of the puzzle are cleariy still missing and other scenarios exist that have not been explained here, like the RNA-world model suggesting that RNA was the first carrier of biological information and functional peptides evolved oidy later (52). But the more of such suggestions and experimental indications we have, the better we will be able to answer the question of how biological homochirality and finally life on Earth might have evolved. 

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