Derived Subgroups

Other subgroups of alkylating agents are the nitrosoureas (examples carmustine, BCNU lomustine, CCNXJ) and the triazenes (example dacarbazine, DTIC). Platinum derivatives (cisplatin, carboplatin, oxaliplatin) have an action that is analogous to that of alkylating agents (formation of crosslinks) and therefore are appended to this class, as well. 

Plant derivatives comprise several subgroups with diverse mechanisms of action. 

The myosin-II group can be divided into two groups derived from striated muscle and non-muscle/smooth muscle (Cheney et al., 1993). The striated muscle subgroup can be further divided into the forms found in skeletal and cardiac muscles. The myosins from striated and cardiac muscles have different biochemical... 

With the chemical structure of PbTX-1 finally known and coordinates for the molecule available from the dimethyl acetal structure, we wanted to return to the natural product crystal structure. From the similarities in unit cells, we assumed that the structures were nearly isomorphous. Structures that are isomorphous are crystallographically similar in all respects, except where they differ chemically. The difference between the derivative structure in space group C2 and the natural product structure in P2. (a subgroup of C2) was that the C-centering translational symmetry was obeyed by most, but not all atoms in the natural product crystal. We proceeded from the beginning with direct methods, using the known orientation of the PbTX-1 dimethyl acetal skeleton (assuming isomorphism) to estimate phase... 

HIV strains are grouped according to the preferred site of replication. T-tropic viruses prefer replication in T lymphocytes and M-tropic viruses in macrophages. Use of chemokine receptors differs for each subgroup CXCR4 (or fusin, the receptor for stromal cell-derived factor [SDF-1]) for T-tropic viruses and CCR5 (the receptor... 

Most of the evidence supporting a role for HA in the control of wakefulness is derived from pharmacological studies. For ease of reference, these studies are divided into subgroups and detailed below. 

Reference Concentration (RfC)—An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious noncancer health effects during a lifetime. The inhalation reference concentration is for continuous inhalation exposures and is appropriately expressed in units of mg/m3 or ppm. The RfC is operationally derived from the No-Observed-Adverse-Effect Level (NOAEL- from animal and human studies) by a consistent application of uncertainty factors that reflect various types of data used to estimate RfCs and an additional modifying factor, which is based on a professional judgment of the entire database on the chemical. The RfCs are not applicable to nonthreshold effects such as cancer. 

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